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Biophotonics
Gerd Keiser
Concepts to Applications
Second Edition
Graduate Texts in Physics

Graduate Texts in Physics
Series Editors
Kurt H. Becker, NYU Polytechnic School of Engineering, Brooklyn, NY, USA
Jean-Marc Di Meglio, Matière et Systèmes Complexes, Bâtiment Condorcet,
UniversitéParis Diderot, Paris, France
Sadri Hassani, Department of Physics, Illinois State University, Normal, IL, USA
Morten Hjorth-Jensen, Department of Physics, Blindern, University of Oslo, Oslo,
Norway
Bill Munro, NTT Basic Research Laboratories, Atsugi, Japan
Richard Needs, Cavendish Laboratory, University of Cambridge, Cambridge, UK
William T. Rhodes, Department of Computer and Electrical Engineering and
Computer Science, Florida Atlantic University, Boca Raton, FL, USA
Susan Scott, Australian National University, Acton, Australia
H. Eugene Stanley, Center for Polymer Studies, Physics Department, Boston
University, Boston, MA, USA
Martin Stutzmann, Walter Schottky Institute, Technical University of Munich,
Garching, Germany
Andreas Wipf, Institute of Theoretical Physics, Friedrich-Schiller-University Jena,
Jena, Germany

Graduate Texts in Physicspublishes core learning/teaching material for graduate- and
advanced-level undergraduate courses on topics of current and emergingﬁelds within
physics, both pure and applied. These textbooks serve students at the MS- or
PhD-level and their instructors as comprehensive sources of principles, deﬁnitions,
derivations, experiments and applications (as relevant) for their mastery and teaching,
respectively. International in scope and relevance, the textbooks correspond to course
syllabi sufﬁciently to serve as required reading. Their didactic style, comprehensive-
ness and coverage of fundamental material also make them suitable as introductions or
references for scientists entering, or requiring timely knowledge of, a researchﬁeld.

Gerd Keiser
Biophotonics
Concepts to Applications
Second Edition
123

Gerd Keiser
Department of Electrical and Computer
Engineering
Boston University
Newton, MA, USA
ISSN 1
ISSN1 868-4521 (electronic)
Graduate Texts in Physics
ISBN 978-981-19-3481-0 ISBN 978-981-19-3482-7 (eBook)
https://doi.org/10.1007/978-981-19-3482-7
1
st
edition:©Springer Science+Business Media Singapore 2016
2
nd
edition:©The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature
Singapore Pte Ltd. 2022
This work is subject to copyright. All rights are solely and exclusively licensed by the Publisher, whether
the whole or part of the material is concerned, speciﬁcally the rights of translation, reprinting, reuse of
illustrations, recitation, broadcasting, reproduction on microﬁlms or in any other physical way, and
transmission or information storage and retrieval, electronic adaptation, computer software, or by similar
or dissimilar methodology now known or hereafter developed.
The use of general descriptive names, registered names, trademarks, service marks, etc. in this
publication does not imply, even in the absence of a speciﬁc statement, that such names are exempt from
the relevant protective laws and regulations and therefore free for general use.
The publisher, the authors, and the editors are safe to assume that the advice and information in this
book are believed to be true and accurate at the date of publication. Neither the publisher nor the
authors or the editors give a warranty, expressed or implied, with respect to the material contained
herein or for any errors or omissions that may have been made. The publisher remains neutral with regard
to jurisdictional claims in published maps and institutional afﬁliations.
This Springer imprint is published by the registered company Springer Nature Singapore Pte Ltd.
The registered company address is: 152 Beach Road, #21-01/04 Gateway East, Singapore 189721,
Singapore

To
Ching-Yun, Nishla, Keith, Kai, and Neyla for
their loving patience and encouragement

Preface
vii
The discipline of biophotonics or biomedical optics has undergone a fascinating
journey in the past several decades, and it is still growing rapidly. As the name
biophotonicsimplies, this discipline deals with the interaction between light and
biological material. The application of thisﬁeld to biological disciplines is based on
a wide range of photonic technologies. These technologies involve the generation,
detection, and control of photons for enabling functions such as transferring or
processing information, analyzing biomaterial characteristics, sensing or measuring
changes in biological tissue parameters, and modifying biomaterial characteristics.
The resulting interactions can be used in almost all biomedical areas for basic life
science research and for biomedical diagnosis, therapy, monitoring, imaging, and
surgery.
Owing to the importance of biophotonics to all aspects of human health, it is
essential that a wide range of biomedical researchers, healthcare professionals,
clinical technicians, and biomedical engineers have a good understanding of bio-
photonics and its applications. To address the attainment and implementation
of these skills, this book provides the basic material for a one-semester course in the
fundamentals and applications of biophotonic technology for senior or postgraduate
students. It also will serve well as a working reference or as a short-course textbook
for biomedical researchers, practicing physicians, healthcare professionals, clinical
technicians, and biomedical engineers and technicians dealing with the design,
development, and application of photonic components and instrumentation to
biophotonic issues.
In C
1–5, t he sequence of topics takes the reader systematically from the
underlying principles of light and biology, through the fundamentals of opticalﬁber
light guiding, and then through optical sources and photodetection methods. Next,
the topics in Chaps.6–10address the concepts of light–tissue interactions, various
optical probes and photonic sensing techniques, the principles of microscopy and
spectroscopy, and biophotonic imaging modalities. Theﬁnal chapter discusses
advanced techniques and developments such as optical trapping, miniaturized
lab-on-a-chip instruments, photonics in dentistry, the principles of time-correlated
single photon counting, smartphone spectrometers, wearable biophotonic body
sensors, robotic surgery, and optogenetics procedures. By mastering these funda-
mental topics, the reader will be prepared not only to contribute to current

Newton,MA, USA Gerd Keiser
biomedical photonics disciplines, but also to understand quickly any further tech-
nology developments for future enhanced biophotonic developments.
viii Preface
The background required to study the book is that of typical senior-level engi-
neering students. This background includes introductory biology and chemistry,
calculus, and basic concepts of electromagnetics and optics as presented in a
freshman physics course. To assist readers in learning the material and applying it
to practical situations, 106 worked examples are given throughout the text. A col-
lection of 126 homework problems is included to test the readers’comprehension
of the material covered, and to extend and elucidate the text.
The a
nd books cited as references in the text were selected from among
numerous texts and thousands of papers in the literature relating to the material
covered in each chapter. Because biophotonics brings together research, develop-
ment, and application efforts from many different scientiﬁc, medical, and engi-
neering disciplines, these references are a small sample of the major contributions to
biophotonics. A number of these references are review and tutorial papers and
provide a starting point for delving deeper into any given topic.

Newton, MA, USA Gerd Keiser
ix
Acknowledgments
In preparing this book on biophotonics, I am extremely grateful to the many people
worldwide with whom I had countless beneﬁcial discussions and who helped me in
many different ways. These people are too numerous to mention individually, but I
truly appreciate their help. They include university professors, scientists, and
engineers in industry and researcher organizations, students, component and
equipment sales and marketing personnel, and the countless authors of journal
articles who investigated and reported on developments of the material in this book.
In addition, I would like to thank Loyola D’Silva of Springer for his assistance
and expert guidance, together with the other editorial and production team members
of Springer, to produce the book. As aﬁnal personal note, I am grateful to my wife
Ching-Yun and my family members Nishla, Keith, Kai, and Neyla for their patience
and encouragement during the time I devoted to writing this book.

Contents
xi
1Overview of Biophotonics................................ 1
1.1What Is Biophotonics?
............................. 3
1.2Diverse Applications
............................... 6
1.3Biophotonic Spectral Windows
....................... 9
1.4Light Absorption
.................................. 12
1.5Decibel Notation for Signal Attenuation
................. 13
1.6Structures of Biological Cells and Tissues
............... 16
1.6.1Macromolecules
............................ 17
1.6.2Biological Cells
............................ 20
1.6.3Mitochondria
.............................. 20
1.6.4Biological Tissues and Organs
.................. 21
1.7Summary
....................................... 23
References
............................................ 24
2Basic Principles of Light
................................. 27
2.1Lightwave Characteristics
........................... 28
2.1.1Monochromatic Waves
....................... 29
2.1.2Pulsed Plane Waves
......................... 31
2.2Polarization
...................................... 31
2.2.1Linear Polarization
.......................... 33
2.2.2Elliptical and Circular Polarization
............... 35
2.3Quantized Photon Energy and Momentum
............... 37
2.4Reﬂection and Refraction
........................... 40
2.4.1Snells’Law
............................... 40
2.4.2The Fresnel Equations
....................... 42
2.4.3Diffuse Reﬂection
........................... 46
2.5Interference
...................................... 47
2.6Optical Coherence
................................. 48
2.7Lightwave-Molecular Dipole Interaction
................. 50
2.8Summary
....................................... 51
References
............................................ 54

xii Contents
3Optical Fibers for Biophotonic Applications.................. 55
3.1Light Guiding Principles in Conventional Optical Fibers
.....56
3.1.1Ray Optics Concepts
........................ 60
3.1.2Modal Concepts
............................ 62
3.1.3Mode Field Diameter
........................ 67
3.1.4Effective Refractive Index
..................... 69
3.2Graded-Index Optical Fibers
......................... 69
3.2.1Core Index Structure
......................... 69
3.2.2Graded-Index Numerical Aperture
............... 70
3.2.3Cutoff Condition in Graded-Index Fibers
.......... 71
3.3Performance Characteristics of Generic Optical Fibers
.......71
3.3.1Attenuation Versus Wavelength
................. 71
3.3.2Mechanical Properties
........................ 72
3.3.3Optical Power-Handling Capability
.............. 72
3.3.4Biocompatibility of Fibers for Medical Use
........73
3.4Conventional Solid-Core Fibers
....................... 73
3.5Specialty Solid-Core Fibers
.......................... 75
3.5.1Photosensitive Optical Fiber
................... 75
3.5.2Fibers Resistant to UV-Induced Darkening
.........77
3.5.3Bend Insensitive Fiber
....................... 77
3.5.4Polarization-Maintaining Fiber
.................. 79
3.6Double-Clad Fibers
................................ 81
3.7Hard-Clad Silica Fibers
............................. 82
3.8Coated Hollow-Core Fibers
.......................... 83
3.9Photonic Crystal Fibers
............................. 84
3.10Plastic Fibers
.................................... 85
3.11Side-Emitting or Glowing Fibers
...................... 86
3.12Middle-Infrared Fibers
.............................. 87
3.13Tapered Optical Fibers
............................. 89
3.14Optical Fiber Bundles
.............................. 90
3.15Summary
....................................... 91
References
............................................ 94
4Fundamentals of Light Sources
............................ 97
4.1Radiometry
...................................... 99
4.1.1Radiant Energy
............................. 100
4.1.2Radiant Optical Flux and Power
................ 100
4.1.3Irradiance or Exposure Rate
................... 100
4.1.4Radiant Intensity
........................... 101
4.1.5Radiant Exposure or Radiant Fluence
............103
4.1.6Radiance
................................. 103
4.2A
amps
...................................... 104

Contents xiii
4.3Light-Emitting Diodes (LEDs) ........................ 106
4.3.1LED Operation and Structures
.................. 106
4.3.2LED Wavelengths and Device Uses
.............. 108
4.3.3Modulation of an LED
....................... 110
4.4Lasers for Biophotonics
............................. 113
4.4.1Basic Laser Actions
......................... 114
4.4.2Laser Diodes
.............................. 117
4.4.3External Modulation of Semiconductor Lasers
......120
4.4.4Solid-State Lasers
........................... 121
4.4.5Gas Lasers
................................ 122
4.4.6Optical Fiber Lasers
......................... 124
4.5Supercontinuum Light Sources
........................ 125
4.6Summary
....................................... 126
References
............................................ 128
5Fundamentals of Optical Detectors
......................... 131
5.1ThepinPhotodetector
.............................. 132
5.2Avalanche Photodiodes
............................. 139
5.3Photodiode Noises
................................ 141
5.3.1Signal-to-Noise Ratio
........................ 141
5.3.2Sources of Photodetector Noise
................. 142
5.3.3Signal-to-Noise Ratio Limits
................... 145
5.3.4Noise-Equivalent Power and Detectivity
..........147
5.3.5Photodiode Linear Response
................... 148
5.3.6Comparisons of Photodiodes
................... 149
5.4Multichannel Detectors
............................. 150
5.4.1CCD Array Technology
...................... 150
5.4.2CMOS Array Technology
..................... 152
5.4.3Scientiﬁc CMOS
........................... 153
5.5High-Performance Detectors
......................... 153
5.5.1Photomultiplier Tubes (PMT)
.................. 153
5.5.2Silicon Photomultipliers (SiPM)
................ 155
5.6Scientiﬁc Cameras
................................. 156
5.6.1Frontside Versus Backside Illumination
...........156
5.6.2Dynamic Range
............................ 157
5.6.3Resolution
................................ 158
5.6.4Response Speed
............................ 158
5.7Optical Filters
.................................... 159
5.8Optical Couplers and Optical Circulators
................ 162
5.9Summary
....................................... 164
References
............................................ 167

xiv Contents
6Light-Tissue Interactions................................. 169
6.1Reﬂection and Refraction Applications
.................. 172
6.1.1Refraction in Ophthalmology
................... 172
6.1.2Specular Reﬂection
.......................... 173
6.1.3Diffuse Reﬂection
........................... 175
6.2Absorption
...................................... 176
6.2.1Absorption Characteristics
..................... 177
6.2.2Absorption in Biological Tissues
................ 180
6.3Scattering
....................................... 183
6.3.1Elastic Scattering
........................... 186
6.3.2Rayleigh Scattering
.......................... 189
6.3.3Anisotropy Factor
........................... 191
6.3.4Inelastic (Raman) Scattering
................... 192
6.4Scattering with Absorption
.......................... 193
6.5Light-Tissue Interaction Mechanisms
................... 195
6.5.1Photobiomodulation
......................... 199
6.5.2Photochemical Interaction
..................... 202
6.5.3Thermal Interaction
.......................... 205
6.5.4Photoablation
.............................. 209
6.5.5Plasma-Induced Photoablation
.................. 211
6.5.6Photodisruption
............................ 212
6.6Formation of Speckles
.............................. 213
6.7Fluorescence Basics
............................... 214
6.8Summary
....................................... 216
References
............................................ 219
7Optical Probes and Biosensors
............................ 223
7.1Overview of Biosensors and Probes
.................... 224
7.2Optical Fiber Probe Conﬁgurations
.................... 226
7.3Optical Fiber Tip Geometries
......................... 233
7.4Optical Sensors
................................... 237
7.4.1Biorecognition Optical Fiber Sensors
.............237
7.4.2ELISA
................................... 238
7.4.3Sensors Based on Optical Fiber Movements
........239
7.4.4Microbending Fiber Sensors
................... 242
7.5Interferometric Sensors
............................. 243
7.5.1Mach–Zehnder Interferometer
.................. 244
7.5.2Michelson Interferometer
..................... 246
7.5.3Sagnac Interferometer
........................ 248
7.6Photonic Crystal Fiber Biosensors
..................... 249
7.6.1Interferometry Sensing Methods
................ 249
7.6.2Liquid Inﬁltration Sensor
..................... 250
7.7F
ragg Grating Sensors
......................... 251

Contents xv
7.7.1Smart-Bed FBG System ...................... 252
7.7.2Distributed FBG-Based Catheter Sensor
...........252
7.8Surface Plasmon Resonance Biosensors
................. 253
7.9Single Nanoparticle Detection
........................ 254
7.10Summary
....................................... 255
References
............................................ 257
8Microscopy
........................................... 261
8.1Concepts and Principles of Microscopy
................. 262
8.1.1Viewing and Illumination Techniques
............262
8.1.2Observation Methods
........................ 267
8.1.3Numerical Aperture
......................... 269
8.1.4Field of View
.............................. 270
8.1.5Depth of Field
............................. 271
8.2Resolution and Diffraction Limit
...................... 272
8.3Confocal Microscopy
.............................. 276
8.4Fluorescence Microscopy
............................ 278
8.5Multiphoton Microscopy
............................ 281
8.6Raman Microscopy
................................ 283
8.7Light Sheet Fluorescence Microscopy
................... 285
8.8Super-Resolution Fluorescence Microscopy
.............. 286
8.9Expansion Microscopy
............................. 288
8.10Summary
....................................... 289
References
............................................ 291
9Spectroscopic Methodologies
.............................. 293
9.1Fluorescence Spectroscopy
.......................... 295
9.2FRET/FLIM
..................................... 298
9.2.1Förster Resonance Energy Transfer
.............. 298
9.2.2Fluorescence Lifetime Imaging Microscopy
........301
9.3Fluorescence Correlation Spectroscopy
.................. 305
9.4Elastic Scattering Spectroscopy
....................... 309
9.5Diffuse Correlation Spectroscopy
...................... 311
9.6Raman Spectroscopy
............................... 312
9.7Surface Enhanced Raman Scattering Spectroscopy
.........317
9.8Coherent Anti-Stokes Raman Scattering Spectroscopy
.......
318
9.9
............... 320
9.10Photon Correlation Spectroscopy
...................... 321
9.11Fourier Transform Infrared Spectroscopy
................ 323
9.12Brillouin Light-Scattering Spectroscopy
................. 324
9.13Summary
....................................... 325
References
............................................ 328

xvi Contents
10Optical Imaging Procedures.............................. 331
10.1Optical Coherence Tomography
....................... 332
10.1.1Time Domain OCT
.......................... 334
10.1.2Spectral Domain OCT
....................... 341
10.1.3Swept Source OCT
.......................... 342
10.2Endoscopy
...................................... 344
10.2.1Basic Endoscopy
........................... 345
10.2.2Minimally Invasive Surgery
................... 346
10.2.3Tethered Capsule Endomicroscopy
.............. 348
10.2.4Microendoscopy
............................ 348
10.3Laser Speckle Imaging
............................. 350
10.4Optical Coherence Elastography
....................... 353
10.5Photoacoustic Tomography
.......................... 355
10.6Hyperspectral Imaging
.............................. 359
10.7Summary
....................................... 360
References
............................................ 362
11Applications of Biophotonic Technologies
.................... 365
11.1Optical Manipulation
............................... 367
11.2Miniaturized Analyses Tools
......................... 372
11.2.1Microﬂuidic Platforms Using LOC Technology
.....372
11.2.2Lab-on-Fiber Concept
........................ 375
11.3Photonics in Dentistry
.............................. 376
11.3.1Detection of Dental Caries
.................... 376
11.3.2PDT Applications to Periodontal Diseases
.........377
11.4Time-Correlated Single Photon Counting
................ 378
11.5Smartphone Spectrometers
........................... 380
11.6Wearable Biophotonic Body Sensors
................... 381
11.7Optogenetics
..................................... 383
11.8Doppler OCT
.................................... 384
11.9Robotic Surgery
.................................. 385
11.10Summary
....................................... 387
References
............................................ 388
Index
...................................................... 391

About the Author
Dr. Gerd Keiseris a Research Professor at Boston University and a consultant for
the telecom and biophotonics industries at PhotonicsComm Solutions. Previously
he was involved with developing and implementing telecom technologies at
Honeywell, GTE, and General Dynamics. His technical achievements at GTE
earned him the prestigious Leslie Warner Award. In addition, he has served as
Adjunct Professor of Electrical Engineering at Northeastern University, Boston
University, and Tufts University, and was an industrial advisor to the Wentworth
Institute of Technology. Formerly he was a visiting chair professor in the Elec-
tronics Engineering Department at the National Taiwan University of Science and
Technology. He also was a visiting researcher at the Agency for Science, Tech-
nology, and Research (A*STAR) in Singapore and at The University of Melbourne,
Australia. He is an IEEE Life Fellow, an OPTICA Fellow, and a SPIE Fellow. In
addition, he has served as an associate editor and reviewer of several technical
journals, and is the author ofﬁve postgraduate-level books. He received his B.A.
and M.S. degrees in mathematics and physics from the University of Wisconsin and
a Ph.D. in physics from Northeastern University. His professional experience and
research interests are in the general areas of optical networking and biophotonics.
xvii

Abbreviations
xix
ADP Adenosine diphosphate
AMP Adenosine monophosphate
APD Avalanche photodiode
ATP Adenosine triphosphate
BFP Blue ﬂuorescent protein
BLS Brillouin light scattering
CARS Coherent anti-Stokes Raman spectroscopy
CCD Charge-coupled device
CFP Cyan ﬂuorescent protein
CMOS Complementary metal –oxide–semiconductor
CW Continuous wave
DBS Deep brain stimulation
DCF Double-clad ﬁber
DCS Diffuse
correlation
spectroscopy
DFB Distributed feedback (laser)
DIC Differential interference contrast
DNA Deoxyribo
nucleic acid
DOF
Depth ofﬁeld
DPSS Diode-pumped solid state
DR
Dynamic
range
DRS Diffuse re ﬂectanc
e spectroscopy
ELISA
Enzyme-linked immunosorbent
assay
ESS El
astic scattering spectroscopy
ExM Expansion microscopy
FBG Fiber Bragg grating
FCS Fluorescence correlation spectroscopy
FD-OCT Fourier-domain OCT
FEL Free-electron laser
FIDA Fluorescence intensity distribution analysis
FLIM Fluorescence lifetime imaging microscopy
FN Field number
FOV Field of view
FRET Fluorescence resonance energy transfer
FRET F örster
resonance energy transfer

xx Abbreviations
FTIR Fourier transform infrared
FWHM Full-width half-maximum
FWM Four-wave mixing
GFP Green ﬂuorescent protein
GRIN Graded-index
HCPCF Hollow-core photonic crystalﬁber
HCS Hard-clad silica
HE Hybrid electric (mode)
HMFG Heavy metal ﬂuoride glasses
HRCT High-resolution computed tomography
HSI Hyperspectral imaging
IR Infrared
IRIS Interferometric reﬂectance imaging sensor
LED Light emitting diode
LITT Laser-induced interstitial thermotherapy
LLLT Low-level light therapy (photobiomodulation)
LOC Lab-on-a-chip
LOF Lab-on- ﬁber
LP Linearly polarized
LPG Long-period grating
LSFM Light sheetﬂuorescence microscopy
LSPR Localized surface plasmon resonance
LSS Light scattering spectroscopy
MFD Mode- ﬁeld diameter
MI Michelson interferometer
MMF Multimode ﬁber
MOSFET Metal–oxide–semiconductorﬁeld-effect transistor
MRI Magnetic resonance imaging
MZI Mach –Zehnder interferometer
NA Numerical aperture
NCF No-core ﬁber
Nd:YAG Neodymium:yttrium aluminum garnet
NEP Noise equivalent power
NIR Near infrared
NO Nitric oxide
OCE Optical coherence elastography
OCT Optical coherence tomography
OCTA OCT angiography
OPL Optical path length
OSA Optical spectrum analyzer
PALM Photoactivated localization microscopy
PAT Photoacoustic tomography
PCF Photonic crystalﬁber
PCH Ph
oton counting histograms
PCS P
ho ton correlation spectroscopy

Abbreviations xxi
PDL Polarization-dependent loss
PDT Photodynamic therapy
PLA Percutaneous laser ablation
PMMA Polymethylmethacrylate
PMT Photomultiplier tube
POC Point of care
POF Plastic opticalﬁber
POF Polymer optical ﬁber
PSF Point spread function
QCL Quantum cascade laser
RET Resonance energy transfer
RI Refractive index
RNA Ribonucleic acid
ROS Reactive oxygen species
SAPD Silicon APD
sCMOS Scientiﬁc CMOS
SD-OCT Spectral domain OCT
SERS Surface-enhanced Raman scattering
SFG Sum frequency generation
SHG Second-harmonic generation
SIM Structured illumination microscopy
SiPM Silicon photomultiplier
SLD Superluminescent diode
SM Single mode
SMF Singl
e-modeﬁber
SNR
Signal-to-noise ratio
SPR Surface plasmon resonance
SRG Stimulated Raman gain
SRI Surround
ing refractive index
SRL Stim
ulated Raman loss
SRS Stimulated Raman scattering
SS-OCT Swept source OCT
STED Stimulated emission depletion microscopy
STORM Stochastic optical reconstruction microscopy
TCSPC Time-correlated single photon counting
TD-OCT Time-domain OCT
TE Transverse electric
TFF Thin- ﬁlmﬁlter
THG Third-harmonic generation
TIR Total internal reﬂection
TM Transverse magnetic (mode)
TPEF Two-photon excitationﬂuorescence
TRT Thermal relaxation time
UV Ul
traviolet
VCSEL V
ertical-cavity surface-emitting laser

xxii Abbreviations
WDL Wavelength-dependent loss
YAG Yt
trium aluminum garnet
YFP Y
ell owﬂuorescent protein

1
Overview of Biophotonics
Abstract
Biophotonics or biomedical optics has become an indispensable tool for basic
life sciences research and for biomedical diagnosis, therapy, monitoring,
imaging, and surgery. This chapterﬁrst describes what biophotonics is and what
its beneﬁts and applications are. Then some basic concepts of light and of
light-tissue interactions are described, including what speciﬁc lightwave
windows are needed to carry out biophotonic processes. Theﬁnal section gives
a brief tutorial of biological cell and molecular structures, cellular and molecular
functions, and the vocabulary used to describe these structures and functions.
This topic is essential for understanding the biophotonic tools and light-tissue
interaction processes described in this book.
Throughout the history of the world, humans have always been fascinated by the
power and importance of light. This fascination appears in religious writings and
rituals, in art and literary works ranging from ancient to modern, in lights for
buildings and vehicles, in a wide variety of displays for computing and commu-
nication devices, and in the dramatic visualization effects of cinematography and
other entertainment settings. Analogous to the use of electrons in the electronics
world, photons are the key enabling entities in the world of light-based technology
or photonics. Photonics is the discipline that involves the generation, detection, and
control of photons for enabling functions such as transferring or processing
information, sensing or measuring changes in physical parameters, and physically
modifying material characteristics. The applications of photonics are found in
almost every technical discipline including illumination, imaging, manufacturing,
material processing, telecommunications, data storage, displays, photography,
forensics, power generation, bar codes, and quick response (QR) codes for
smartphones.
1©T
G. Keiser,Biophotonics, Graduate Texts in Physics,
https://doi.org/10.1007/978-981-19-3482-7_1

s
2 1 Overview of Biophotonics
Biological tissueIncident light
Reflection
Fluorescence
Scattering
Tissue modifications/therapy
Reflection
Absorption
Fig. 1.1Biophotonics involves all aspects of light-tissue interactions
Photonic technology also has become an indispensable tool for basic life sci-
ences research and for biomedical diagnosis, therapy, monitoring, imaging, and
surgery. This category of photonics deals with the interaction between light and
biological material and is referred to asbiophotonicsorbiomedical optics.A
indicated in Fig.1.1, the resulting reﬂection, absorption,ﬂuorescence, and scat-
tering manifestations of this interaction can be used to analyze the characteristics of
healthy and diseased biological tissues and to carry out tissue modiﬁcations and
therapy. The purpose of this chapter is to give an overview of this rapidly growing
multidisciplinaryﬁeld and to note its dramatically increasing uses, which are
addressed in the following chapters.
In this chapter, First Sect.1.1describes what biophotonics is and what its
beneﬁts are. Next Sect.1.2gives an overview of the areas where biophotonics is
used. Of particular interest in this book are biophotonic implementations in
biomedical research and clinical practices. Among the numerous diverse applica-
tions are various biomedical imaging techniques, microscopic and spectroscopic
procedures, endoscopy, tissue pathology, bloodﬂow monitoring, light therapy,
biosensing, laser surgery, dentistry, and health status monitoring.
Then S t.1.3gives some basic concepts of light and of light-tissue interactions.
This section also describes the fundamental background as to why speciﬁc light-
wave windows are needed to carry out most biophotonic processes. The light-tissue
interaction topic is expanded on in Chap.6. The topics of Sects.1.4and1.5cover
the characteristics of light absorption as a function of the wavelength of light and
describe the fundamental units for measuring light signal power reduction in optical
links and components. Finally, Sect.1.6g rief tutorial of biological cell and
molecular structures, cellular and molecular functions, and the vocabulary used to
describe these structures and functions. These topics are essential to understanding
the biophotonic tools and light-tissue interaction processes described in this book.

1.1 What Is Biophotonics? 3
1.1 What Is Biophotonics?
Biophotonics is a multidisciplinaryﬁeld that deals with all aspects of the interac-
tions between light and biological material [1–12]. As Fig.1.2illustrates, bio-
photonics draws from the resources of many technicalﬁelds, including biology,
biotechnology, chemistry, physics, various engineeringﬁelds, and basically every
medical discipline. From a global viewpoint, biophotonics refers to the detection,
reﬂection, emission, modiﬁcation, absorption, creation, and manipulation of pho-
tons as they interact with biological cells, organisms, molecules, tissues, and sub-
stances. The applications of biophotonic processes to biomedical issues include
(a) 2D and 3D imaging of cells, tissues, and organs, (b) noninvasive measurements
of biometric parameters such as blood oxygen and glucose levels, (c) therapeutic
photonic treatment of injured, diseased, or unwanted cells, (d) detection of injured
or diseased cells and tissue, (e) monitoring of wound healing and progress of
therapeutic treatments, and (f) surgical procedures such as laser cutting, tissue
ablation, and removal of cells and tissue.
The technologies supporting biophotonics include opticalﬁbers, optical sources
and photodetectors, test and measurement instrumentation, nanotechnology,
microscopy, spectroscopy, and miniaturization methodologies. Therefore, biopho-
tonics combines a wide variety of optical methods to investigate the structural,
functional, mechanical, biological, and chemical properties of biological material
and systems. In addition, biophotonic methodologies are being used extensively to
investigate and monitor the health and wellbeing of humans. The wavelengths used
Biology
Biotechnology
Chemistry Physics
Engineering Medicine
Molecules
Organelles
Cells
Tissue
Organs
Pharmaceuticals
Tissue repair
Biometrics
Biosensing
Chemical bonds
Chemical structures
Material properties
Reactions
Optics
Lasers/LEDs
Photodetection
Optical fibers
Acoustics
Electrical
Measurements
Packaging
Fluid mechanics
Cardiology
Dermatology
Oncology
Ophthalmology
Biophotonics
Fig. 1.2Biophotonics draws from the resources of many technicalﬁelds

for biophotonics typically range from 190 nm in the ultraviolet to 10.6lm in the
infrared region, with numerous applications being in the visible 400–700 nm
spectrum. Thus, a broad range of diverse tools and techniques are employed in
biophotonics.
4 1 Overview of Biophotonics
Several terms are commonly used when studying the characteristics ofbiol ogical
cells, molecules, or tissues or when determining the behavior of such biological
samples when they are exposed to various external stimuli. These terms include the
following expressions.
In vivo: The term in vivo (Latin for“in the living”) refers to tests or procedures
on isolated biological components within whole, living organisms such as ani-
mals, humans, or plants. Such tests allow the observation of the condition, the
temporal changes, or the effects of an experiment on biological components
within a living entity in its natural surroundings.
In vitro: The term in vitro (Latin for“within the glass”) refers to tests done in a
laboratory setting on biological components that have been extracted from a
living organism. These tests often are made using containers such as glass test
tubes,ﬂasks, and petri dishes. Thus the in vitro evaluations are done on
microorganisms, cells, molecules, or tissue samples outside of their normal
biological environment.
Ex vivo: The term ex vivo (Latin for“from the living”) refers to procedures that
typically involve taking living cells, tissues, or an organ from an organism and
examining, modifying, or repairing these biological components in a controlled
environment under sterile conditions with minimal alteration of the natural
conditions from which the samples originated.
There are several aspects of light that make it a powerful tool in the life sciences
and medicine.
The use of photonic techniques in biophotonics research allows contactless
measurements to be made on a tissue sample or within a cell or molecule with no
or minimal disturbance of the biological activity. Many either contactless or
minimally invasive biomedical procedures can be carried out in a clinical
environment. For example, a light source and a camera can be positioned close
to the biological tissue of an evaluation or treatment site for in vivo contactless
procedures.
In a
c techniques are widely used in surgery and other medical
disciplines. For example, in minimally invasive surgery (also called laparoscopic
or endoscopic surgery) a thin opticalﬁber viewing and illumination probe and
associated miniaturized surgical instruments can be inserted through a natural
body opening (such as the mouth or nostrils) or through one or more minor
incisions in the body for minimally invasive procedures. The surgical tools can
include miniature forceps, probes, scissors, dissectors, hooks, and extractors.
A generic example of a minimally invasive procedure that can be used for treating
diseases in areas such as the abdomen, heart, kidney, or lungs is shown in Fig.1.3.

1.1 What Is Biophotonics? 5
Example body region:
Abdomen, heart,
kidney, lungs
Surgical instruments;
Forceps, scissors, probes,
dissectors, hooks, extractors
Optical fiber viewing
and illumination probe
Viewing scope
or camera
Natural openings
or minor incisions
in the body
Fig. 1.3Example of a minimally invasive surgery procedure with an opticalﬁber probe and
miniature surgical tools
A large selection of ultrasensitive photonic and biophotonic detection instru-
ments can be used over spatial scales covering six orders of magnitude from
fractions of a nanometer to centimeters. Table1.1shows examples of the sizes of
some biological components and measurement aids. The biological components
that can be observed, treated, or manipulated vary from microscopic
nanometer-sized molecules to macroscopic tissue samples.
As Table1.2shows, the measurement time scales for life sciences research
techniques and for biomedical processescan varyfrom femtoseconds (10
−15
s)
Table 1.1Example sizes of some biological components and measurement aids
Component Generic size
Molecule Water molecule: 0.29 nm
Glucose: 0.70 nm
Amino acid: 0.80 nm
Virus 30–100 nm
Bacteria Typical: 0.2lm in diameter and 2–8lm in length
Cells Human red blood cell: 9lm
Eukaryotic cell: 10–20lm
Tissue
sample
1 mm to 1 cm (nominal)
NanoparticleAn example probe consists of an array of 450-nm diameter nanoparticles with
center-to-center spacing of 900 nm
OpticalﬁberUsed for delivering and collecting light; core sizes can range from 9lmto
several mm
Needle
probe
30-gauge n n conjunction with an internal opticalﬁber probe;
312lm outer diameter (nominal)

to hours (10
3
s). Such a broad temporal range can be satisﬁed by a variety of
photonic devices. For example, as Chap.4describes, ultrafast lasers that can
emit short pulse durations (e.g., a few femtoseconds) are available for use in
applications such asﬂuorescence spectroscopy where the pulse width needs to
be shorter than the desired time-resolution measurement. At the other time
extreme, highly stable lasers are available for processes in which a relatively
constant light output is required for measurements and monitoring of processes
that take place over periods of several hours.
6 1 Overview of Biophotonics
Table 1.2Photonic techniques used in biophotonics cover time scales of over 18 orders of
magnitude
Technique Generic time duration and application
Spectroscopy Fluorescentdecayprocesses occur in 10
–15
s
Plasma-induced ablation100 fs–500 ps exposures for dentistry and ophthalmology
Photoablation 10–100 ns treatments in ophthalmology
Thermal irradiation 1ls–1 min exposures for coagulation and tissue vaporization
Photodynamic therapy 5–40 min of light exposure for cancer treatments
Photobiomodulation Minutes to hours for therapeutic or cosmetic effects
1.2 Diverse Applications
Among the disciplinesthat use biophotonic tools and techniques are biomedical
research, clinicalprocedures, dentistry, drug development, healthcare, environ-
mental monitoring, food safety, and manufacturing process control, as Fig.1.4
illustrates [2,13–24].
Biomedical
research
Clinical
procedures
Biophotonics
tools and
techniques
POC tests
and analyses
Environmental
monitoring
Manufacturing
processes
controls
Drug
development
Food safetyDentistry
Fig. 1.4Applications of biophotonic tools and techniques

1.2 Diverse Applications 7
Biomedical research: Biophotonic tools and techniques are being used to
understand the basic functions of cells and molecules in life sciences, to discover
the genesis of diseases in order to devise processes for their early detection, to
develop targeted therapies and minimally invasive treatments, and to monitor
health conditions for the prevention or control of diseases.
Clinical procedures: Almost every medical specialty makes use of some aspect
of biophotonic tools and techniques. Table1.3lists some examples from a range
of clinical procedures. In many of these disciplines the use of miniaturized
optical components together with fast photonic devices have made dramatic
improvements in response times and measurement accuracies.
Dentistry: The biophotonic concepts of laser-tissue interactions are having
widespread uses in dentistry for precisely focusing lasers at speciﬁc points in
hard dental enamel and bone without damaging the surrounding tissue to remove
infected tissue and to prepare teeth forﬁllings or crowns. Other laser applications
in dentistry include gum surgery, root canal sterilization, treatment of oral cavity
ulcers, and whitening of teeth.
Drug development: Processes such asﬂow cytometry,ﬂuorescence detection
methods toﬁnd out whether biological reactions are taking place in drug can-
didates, the use of photo-switchable inhibitory peptides that can be used to
manipulate protein–protein interactions inside cells by applying light, and sur-
face plasmon resonance techniques for rapidly assessing biological reactions in
candidate drug compounds have become effective pharmaceutical research and
development tools.
Point of care (POC) tests and analyses: Point of care testing or diagnostics is a
broad term that refers to the delivery of healthcare evaluations, products, and
services by clinicians to patients at the time of care. Photonic-based devices
include ophthalmological instruments, optical oximeters, compact portable
microscopes, microscopes running on smartphones,ﬂuorescent imagingﬂow
cytometers on a smartphone, and webcam-based biosensors.
Environmental monitoring: Biophotonic spectroscopic techniques and tools
(including the use of spectrometric add-ons to smartphones) are being used to
measure and monitor concentrations of airborne particles in the atmosphere (e.g.,
ﬁne dust, pollens, and chemical pollutants) and to detect pathogens (e.g., bac-
teria, viruses, and protozoa) in bodies of water.
Food safety: Concerns about food safety (e.g., the presence of contaminants and
natural pathogens, food fraud, and food adulteration) are being addressed
through biophotonic techniques and tools such as high-performance chro-
matography, Fourier transform infrared spectroscopy, surface-enhanced Raman
spectroscopy, and biosensors.
Manufa
ntrol: Spectroscopic techniques are being used and
developed further for the non-contact, non-destructive compositional analyses
and quality control of complex biological material used in the manufacturing of
pharmaceutical, nutritional, and cosmetic products.

8 1 Overview of Biophotonics
Table 1.3Uses of biophotonic tools and techniques in selected medical specialties
Medical specialty Applications of biophotonic methodologies
Photobiomodulation: uses low irradiance
levels to aidin
pain relief and tissue healing
Photonic stimulation of tissue to alleviate
acute and chronic pain, treat sprains and
strains from sports injuries, speed up wound
healing, treat nerve and brain injuries, and
promote tissue and bone healing
Cardiology: deals with diseases and
abnormalities of the heart
Use of lasers for imaging lesions in arteries,
diagnosing heart functions, monitoring laser
surgery of irregular heart rhythms, or
reducing cardiac pain
Dentistry: deals with tooth repair and the
prevention, diagnosis, and treatment of tooth
and gum disorders
Detection of caries and cracks in teeth, soft
and hard tissue ablation, endodontic therapy,
tooth restoration treatments, and detection
and treatment of diseases of the teeth, gums,
and mouth structures
Dermatology: deals with the skin and its
disorders and diseases
Treatment of skin atrophy, skin thickening,
varicose veins, vascular lesions, unwanted
hair, age spots, surgical and acne scars, and
pigmented lesions
Gastroenterology: focuses on the digestive
system and its disorders and diseases
Use of endoscopes for imaging the lower and
upper gastrointestinal tract to detect
abnormalities; use of lasers to destroy
esophageal and gastric cancers;
photocoagulation of hemorrhaging peptic
ulcers
Oncology: deals with the study and treatment
of tumors
Early and accurate non-invasive in vivo
cancer detection and diagnosis through a
variety of optical methods for tissue
diagnosis, treatment of cancer through
photodynamic therapy, identiﬁcation of
cancer site boundaries
Ophthalmology: deals with eye structures,
functions, and diseases
Retinal surgery (treatment of cataracts,
glaucoma, and age-related macular
degeneracy), refractive corneal surgery,
imaging of retinal nerveﬁber layers, and
sensing changes in eye anatomy and
physiology
Neurophotonics/Optogenetics: deals with the
structure or function of the nervous system
and brain
The neuroscience discipline of optogenetics
uses light to activate or inhibit signaling
among neurons to study the link between
neural network operation and behavioral or
sensory functions to treat neuropsychiatric
diseases
Vascular medicineorangiology:
deals with
preventing, diagnosing, and treating vascular
and blood vessel related diseases
Use o
asers and opticalﬁbers for imaging
lesions in arteries, diagnosing
microcirculation, treating varicose veins, and
treating diseases of the circulatory and
lymphatic systems, i.e., arteries, veins, and
lymphatic vessels

Table 1.4Indices of
1.3 Biophotonic Spectral Windows 9
1.3 Biophotonic Spectral Windows
As described in Sect.2.1, light propagates in the form of electromagnetic waves [25–
28]. In free space, light travels at a constant speed designated by the letter c, where
c = 299,792,458 m/s (or approximately 310
8
m/s). In biophotonics the
free-space speed of light could be expressed in units such as 30 cm/ns, 0.3 mm/ps, or
0.3lm/fs. The speed of light in free space is related to the wavelengthkand the wave
frequencymthrough the equation c =mk. Upon entering a transparent or translucent
dielectric medium or a biological tissue the lightwave will travel at a slower speed s.
The ratio between c and the speed s at which light travels in a material is called the
refractive index(RI orindex of refraction) n of the material (with n1), so that
s¼c=n ð1:1Þ
Table1.4lists the indices of refraction for a variety of substances. Note that in
many cases the refractive index changes with wavelength.
Example 1.1
If a biological tissue sample has a refractive index n = 1.36, what is the speed
of light in this medium?
Solution: From Eq. (1.1) the speed of light in this tissue sample is
s¼
c
n
¼
310
8
1:36
¼2:2110
8
m/s¼22.1 cm/ns
refraction for various
substances
Material Refractive index
Air 1.000
Water 1.333
Cornea 1.376
Cytoplasm 1.350–1.375
Epidermis 1.34–1.43
Extracellularﬂuids 1.35–1.36
Human liver 1.367–1.380
Melanin 1.60–1.70
Mitochondria 1.38–1.41
Tooth enamel 1.62–1.73
Whole blood 1.355–1

Also shown in Fig.1.5is the relationshipbetween the energy E of a photon and
its frequency (or wavelength), which is determined by the equation known as
Planck’s Law
10 1 Overview of Biophotonics
Figure1.5shows the spectral range covered by optical wavelengths. The
ultraviolet (UV) region ranges from 10 to 400 nm, the visible spectrum runs from
the 400 nm violet to the 700 nm red wavelengths, and the infrared (IR) region
ranges from 700 nm to 300lm. Biophotonic disciplines are concerned mainly with
wavelengths falling into the spectrum ranging from the mid-UV (about 190 nm) to
the mid-IR (about 10lm).
E¼hm¼
hc
k
ð1:2Þ
where the parameterh= 6.63 10
−34
J s = 4.14 10
−15
eV s is Planck’s con-
stant.Theunit Jmeansjoules and the unit eV stands for electron volts. In terms of
wavelength (measured in units oflm), the energy in electron volts is given by
EeVðÞ¼
1:2406
kðlmÞ
ð1:3Þ
10
-2
10
10
10
8
10
18
10
16
10
14
10
12
10
3
Frequency
(Hz)
Photon energy (eV)
Wavelength
(m)
HF/UHF/VHF Radio Microwaves X rays
Infrared 0.7 μm to 1 mm
Biophotonics
190 nm to 10.6 μm
(6.529 to 0.117 eV)
Ultraviolet
Visible light
400-700 nm
10
-4
10
-8
10
-6
10
-3
10
-5
0.1 10
1
Fig. 1.5Location of the biophotonics discipline in the electromagnetic spectrum

1.3 Biophotonic Spectral Windows 11
Table 1.5Wavelength and photon energy ranges for various optical spectrum bands (Spectral
band ranges from Document ISO-21348 of the International Standards Organization)
Band designation Wavelength range (nm) Photon energyrange
(eV)
UV-C 100–280 12.4–4.43
UV-B 280–315 4.43–3.94
UV-A 315–400 3.94–3.10
Visible 400–700 3.10–1.63
Near infrared (IR-A) 700–1400 1.63–0.89
Mid infrared (IR-B) 1400–3000 0.89–0.41
Table1.5lists the correspondence between the wavelength range and the range
of photon energies for various biophotonic spectral bands. The spectral band ranges
listed in the literature often vary slightly from those shown in Table1.5, which are
based on the designations given in Document ISO-21348 of the International
Standards Organization. Note that the UV spectral region is partitioned into three
bands that are classiﬁed as UV-C, UV-B, and UV-A. The reason for these desig-
nations is that the UV light energy is stronger than visible light and its effects are
different in each band. Natural sunlight at the surface of the earth contains mainly
UV-A and some UV-B lightwaves. UV-A light is slightly more energetic than
visible blue light. Many plants use UV-A for healthy growth and, in moderate
doses, UV-A light is responsible for skin tanning. Health concerns for exposure to
UV light are mostly in the UV-B range. The most effective biological wavelength
for producing skin burns is 297 nm. The adverse biological effects increase loga-
rithmically with decreasing wavelength in the UV range, with 330 nm being only
0.1% as effective as 297 nm. Therefore it is quite important to control human
exposure to light in the UV-B range. UV-C light has the highest energy. Although
the sun emits UV-C wavelengths, the upper atmosphereﬁlters out this band, so
there is no exposure to UV-C from sunlight on earth. However, because UV-C light
is used for sterilizing instruments, great care must be exercised to avoid human
exposure to this light.
Example 1.2
Show that photon energies decrease with increasing wavelength. Use wave-
lengths at 850, 1310, and 1550 nm.
Solutio
: F rom Eq. (1.3) it follows that E(850 nm) = 1.46 eV, E
(1310 nm) = 0.95 eV, and E(1550 nm) = 0.80 eV. Thus, the energy
decreases with increasing wavelength.

12 1 Overview of Biophotonics
In relation to Fig.1.5, biophotonic disciplines are concerned mainly with
wavelengths falling into the spectrum ranging from the mid-UV (about 190 nm) to
the mid-IR (about 10.6lm). Generally, because optical properties vary from one
tissue type to another, speciﬁc lightwave windows are needed to carry out most
therapeutic and diagnostic biophotonic processes. Therefore, knowing the details of
these properties allows the speciﬁcation and selection of photonic components that
meet the criteria for carrying out a biological process in a selected optical wave-
length band.
The interaction of light with biological tissues andﬂuids is a complex process
because the constituent materials are optically inhomogeneous. More details on
these effects are given in Chap.6. Owing to the fact that diverse biological tissue
components have different indices of refraction, the refractive index along some
path through a given tissue volume can vary continuously or undergo abrupt
changes at material boundaries, such as atﬂesh and blood vessel interfaces. This
spatial index variation gives rise to scattering, reﬂection, and refraction effects in the
tissue. Although light can penetrate several centimeters into a tissue, strong scat-
tering of light can prevent observers from getting a clear image of tissue charac-
teristics beyond a few millimeters in depth.
1.4 Light Absorption
Light absorption is another important factor in the interaction of light with tissue,
because the degree of absorption determines how far light can penetrate into a
speciﬁc tissue. Figure1.6shows the absorption coefﬁcients as a function of
wavelength for several major tissue components. These components include water
(about 70% of the body), proteins, whole blood, melanin (pigments that give skin,
hair, and eyes their color), and the epidermis (outer layer of the skin). Chapter6
gives more details on absorption in biological tissue.
Most tissues exhibit comparatively low absorption in the spectral range that
extends from 500 nm to about 1500 nm, that is, from the orange region in the
visible spectrum to the near infrared (NIR). This wavelength band is popularly
known as thetherapeutic windowor thediagnostic window, because it enables the
best conditions for viewing or treating tissue regions within a living body by optical
means. Note that although the absorption coefﬁcients for tissue components such as
melanin, blood, and the epidermis are larger than that of water, they have relatively
small concentrations compared to water and thus account for a comparatively small
amount of absorption in the therapeutic window.
Light a
ion characteristics of tissue for regions outside the therapeutic
window are important for implementing functions that depend on high optical
power absorption, such as drilling, cutting, bonding, and ablation of tissue. As
Chap.4discusses, a wide variety of optical sources can be used to carry out these
functions. For example, as is indicated in Fig.1.6, ultraviolet light from ArF or KrF
lasers emitting at wavelengths of 193 and 249 nm, respectively, is strongly

A standardand convenient method for measuring attenuation through an optical
link or an optical device is to reference the output signal level to the input level. For
convenience in calculation, signal attenuation or ampliﬁcation can be designated in
terms of a logarithmic power ratio measured in decibels (dB). The dB unit is
deﬁned by
absorbed in the surface of a tissue and thus can be used for many surgical appli-
cations. In the infrared region, 2940 nm light from an Er: YAG laser is strongly
absorbed by osseous minerals, which makes optical sawing and drilling in bone and
teeth possible. Also in the infrared region, strongly absorbed light from CO2lasers
are used in applications such as surgery, ophthalmology, and cosmetic treatments.
1.5 Decibel Notation for Signal Attenuation 13
Wavelength (μm)
Absorption coefficient (cm
-1
)
1
10
100
1000
0.10 1.00 10.0
KrF
249 nmArF
193 nm
Er:YAG
2940 nm
Diagnostic or
therapeutic
window
Water
Whole
blood
Melanin
Water
0.20 0.50 2.00 5.00
CO
2
10.6 μm
Proteins
Fig. 1.6Absorption coefﬁcients of several major tissue components as a function of wavelength
with example light source emission peaks
1.5 Decibel Notation for Signal Attenuation
Some type of optical link conﬁguration is used for many biophotonic imaging,
therapeutic, monitoring, and tissue evaluation techniques. Such a link typically
contains a light source, an opticalﬁber, a photodetector, and various intermediate
optical components. As an optical signal passes through such a link, the signal loses
a percent of its power within each constituent of the link. An understanding of the
degree of signal attenuation is important for assuring that the correct optical power
level reaches its destination at either the light delivery site or at the photodetector
where the returning light signal is evaluated and interpreted.

Table 1.6Representative
17 9
26 3
35 0
62 5
14 1 Overview of Biophotonics
Power ratio in dB = 10 log
P
out
Pin
ð1:4Þ
where P and P are the input and output optical powers, respectively, to an optical
in out
ﬁber or an optical component and log is the base-10 logarithm. The logarithmic
nature of the decibel allows a large
ratio to be expressed in a fairly simple manner.
Power levels differing by many orders of magnitude can be compared easily through
an addition and subtraction process when they are in decibel form. For example, a
power reduction by a factor of 1000 is a−30 dB loss, an attenuation of 50% is
a−3 dB loss, and a tenfold ampliﬁcation of the power is a gain of +10 dB. Thus an
attractive feature of the decibel is that to measure the changes in the strength of a
signal, the decibel loss or gain numbers in a series of connected optical link elements
between two different points are merely added. Table1.6shows some sample values
of power loss given in decibels and the percent of power remaining after this loss.
Figure1.7shows the relationship between decibels and power ratios that range
from 0.1 to 1.0. The upper dashed line illust
rates that
transmission over a 10-km
distance using aﬁber with an attenuation of 0.5 dB/km results in a 5-dB power
attenuation yielding an output-to-input power ratio of 31.6%. Similarly, over a
10-km distance using aﬁber with an attenuation of 0.3 dB/km results in a 3-dB
power ratio of 50%.
Example 1.3
Assume that after traveling a certain distance in some transmission link, the
power of an optical signal is reduced to half, that is, P
out= 0.5 P
in. What is the
loss in dB of the link?
Solution: From Eq. (1.4) it follows that the attenuation or loss of power is
10 log
P
out
Pin
¼10 log
0:5P
in
Pin
¼10 log 0:5¼100:3?޼ 3dB
values of decibel power loss
and the remaining percentages
Power loss (in dB) Percent of power left
0.1 98
0.5 89
10 10
20 1

1.5 Decibel Notation for Signal Attenuation 15
Power ratio
1.00.50.20.1
Decibels (dB)
0
5
10
3
0.32
0.3 dB/km
0.5 dB/km
Examples for a 10-km
transmission distance
Fig. 1.7The relationship between decibels and power ratios that range from 0.1 to 1.0
The value−3 dB (or a 3-dB loss or attenuation) means that the signal has lost
half its power.
Example 1.4
Consider an optical link that has four optical components hooked together
sequentially. If the losses of these four components are 0.5, 0.1, 1.5, and
0.8 dB, what is the loss in dB of the link?
Solution: The total power loss is found by adding the losses between the two
link end points, that is,
Link loss¼0:5dBþ0:1dBþ1:5dBþ0:8dB¼2:9dB
Because the decibel is used to refer to ratios or relative units, it gives no indi-
cation of the absolute power level. However, a derived unit can be used for this
purpose. Such a unit that is particularly common is the dBm. This unit expresses the
power level P as a logarithmic ratio of P given in mW referred to a base power level
of 1 mW. In this case, the power in dBm is an absolute value deﬁned by
Power level in dBm¼10 log
Pðin mWÞ
1mW
ð1:5Þ

16 1 Overview of Biophotonics
Example 1.5
Consider three different light sources that have the following optical output
powers: 50lW, 1 mW, and 50 mW. What are the power levels in dBm
units?
Solution: Using Eq. (1.5) the power levels in dBm units are−13, 0, and +17
dBm.
Example 1.6
A product data sheet for a certain photodetector states that an optical power
level of−28 dBm is needed at the photodetector to satisfy a speciﬁc per-
formance requirement. What is the required power level inlW (microwatt)
units?
Solution: Eq. (1.5) shows that−28 dBm corresponds to a power inlWof
P¼10
28=10
mW¼0:001585 mW¼1:585lW
1.6 Structures of Biological Cells and Tissues
A basic knowledge of biological cell and molecular structures, cellular and
molecular functions, and the vocabulary used to describe these structures and
functions is essential to understanding the biophotonic tools and light-tissue
interaction processes described in this book. This section gives a brief tutorial of
these concepts [29–32]. The basis of this discussion is the observation that a living
cell consists of about 70% water. The rest of the cell is composed mostly of
macromolecules that are composed of thousands of atoms. First, Sect.1.6.1
d
escribe
s the basic macromolecules, which are the chemical building blocks of the
various components of a cell. Section1.6.2identiﬁes the various components that
make up a cell and describes their different functions depending on where they are
found in a body. The functions of mitochondria are given in Sect.1.6.3. These are
specialized organelles that are found in large numbers in most cells. Then
Sect.1.6.4describes the major categories and functions of biological tissues, which
are ensembles of similar cells.

1.6 Structures of Biological Cells and Tissues 17
1.6.1 Macromolecules
Macromoleculesare large molecules that are made up of selections from a set of
smaller molecular chains such as monomers, glycerin, and fatty acids. As listed in
Table1.7, the four basic groups of macromolecules found in living organisms are
proteins, carbohydrates, nucleic acids, and lipids. Proteins, carbohydrates, and
nucleic acids are known aspolymersbecause they are made up of many molecular
building blocks calledmonomers. Monomers include amino acids for forming
proteins, nucleotides that form nucleic acids, and simple sugars such as glucose and
fructose that are the building blocks for carbohydrates. Lipids are special macro-
molecules that are not polymers.
After water, proteins make up the second largest component in human cells,
tissues, and muscles.Proteinsconsist of one or more long chains of interconnected
monomers called amino acids.Amino acidsare small organic molecules composed
of amine (−NH
2) and carboxylic acid (−COOH)functional groups(groups of
atoms or bonds that are responsible for the characteristic chemical reactions of a
molecule) plusmolecular side chains(called R groups) that are speciﬁc to each
amino acid. The basic elements of an amino acid are carbon, hydrogen, oxygen, and
nitrogen. Amino acids are connected by covalent bonds (referred to aspeptide
bonds) to form chains of molecules calledpolypeptide chains. A protein consists of
one or more of these polypeptide chains that are twisted, wound, and folded upon
themselves to form a macromolecule. Although about 500 amino acids are known,
there are only 20 naturally occurring amino acids.
Proteins are an essential substance of living organisms and participate in almost
every process within cells. Common types of proteins include the following:
Table 1.7The four main groups of macromolecules in living organisms are carbohydrates,
proteins, nucleic acids, and lipids
Carbohydrates Proteins Nucleic acids Lipids
Monomers Monosaccharides:
Examples: glucose,
fructose, galactose
Amino acids:
20 of them
occur naturally
Nucleotides:
Adenine,
thymine, guanine,
cytosine
Triglycerides,
oils, waxes
Polymers Polysaccharides:
Examples: starch,
glycerin, cellulose
Disaccharides:
Examples: sucrose,
maltose, lactose
Proteins,
polypeptides
DNA,
RNA For
triglycerides:
glycerol, fatty
acids
Food
examples
Potatoes, pasta,
dried
and canned
fruits,
rice, grains,
bread,
honey
Meat, eggs,
tofu, soy,
beans, lentils,
dairy products
Beans, asparagus,
peas,
cauliﬂower,
lentils,
spinach,
mushrooms
Cooking o

olives, s
eeds,
avocados, nuts

18 1 Overview of Biophotonics
Enzymesfor catalyzing chemical reactions that are vital to metabolism
Structural proteins(such as keratin found in hair andﬁngernails and collagen)
that provide support for maintaining cell shape. Note thatcollagenis the most
abundant protein in humans and animals. It is made up of long chains of hard,
insoluble, andﬁbrous protein that has great tensile strength and makes up about
one-third of the protein in the human body. Collagen is found in tissues such as
bone, teeth, cartilage, tendon, ligament, and theﬁbrous matrices of skin and
blood vessels.
Antibodiesthat bind to foreign particles orcells and assist in their elimination
from the body
Transport proteinsthat carry compounds or chemicals from one location to
another throughout living systems. An example of a transport protein ishe-
moglobinthat carries oxygen throughout the body by means of the blood.
Carbohydratesare important in deﬁning the structure of cells and are a source of
immediate energy needs in living systems. These macromolecules consist of
interconnected chains or rings of carbon (C), hydrogen (H), and oxygen (O) atoms
with a ratio of H twice that of C and O. Carbohydrates include compounds such as
sugars, starches, and cellulose. The most elementary monomers of carbohydrates
are simple sugars ormonosaccharides. Two fundamental monosaccharides are
glucoseandfructose, which both have the chemical formula C6H
12O
6but have
different chemical structures as shown in Fig.1.8. These simple sugars can combine
with each other to form more complex carbohydrates. Combinations of two simple
sugars are calleddisaccharides(for example, maltose = glucose + glucose and
sucrose = glucose + fructose).Polysaccharidesconsist of a larger number of
simple sugars.
Nucleic acidsare the macromolecules inside of a cell that store and process
genetic or hereditary information by means of protein synthesis. The two principal
forms of nucleic acids that are essential for all forms of life aredeoxyribonucleic
acid(DNA) andribonucleic acid(RNA). The monomers that make up nucleic acids
are callednucleotides. The chemical building blocks of each nucleotide include a
sugar molecule, a nitrogenous base, and a phosphate group, as Fig.1.9illustrates.
Glucose Fructose
C
HO
H
H
C
H
H
OH
OH
CH
2OH
O
C C
OH
HC
CH
2OH
CH
2OH
H
HO
OH
OH H
H
O
C
CC
Fig. 1.8Glucose and fructose are two basic monomers for creating carbohydrates

1.6 Structures of Biological Cells and Tissues 19
Fig. 1.9Basic nucleotide
monomer for creatingnucleic
acids
Nitrogen
base
Sugar
molecule
Phosphate
group
P
O
O O
O
OH
An important nucleotide isadenosine triphosphate(ATP). One molecule of ATP
contains three phosphate groups. A large amount of chemical energy is stored in the
phosphate bonds. When ATP is broken down (hydrolyzed) the energy that is
released is used for many metabolic processes. By using red-light therapy in clinical
trials for speeding up wound healing and mitigating chronic inﬂammation, a cell
can make more ATP (see Chap.6). With more energy, cells can function more
efﬁciently, rejuvenate themselves, and repair damage. Because of this function,
ATP is considered to be a universal energy currency for metabolism.
Lipidsare non-polymer macromolecules that are all insoluble in water. Simple
lipids include fats, phospholipids (e.g., lecithin), and steroids. Fats provide
long-term energy storage and insulation in humans and animals. Fats are composed
of glycerin and fatty acids. As shown in Fig.1.10, a fatty acid is a long chain of
carbon-hydrogen (CH) bonds, with a carboxyl group (COOH) at one end. Phos-
pholipids are found mainly in the cell membranes of living systems and are used for
cell-to-cell signaling. Examples of steroids include cholesterol, estrogen, and
testosterone.
Fig. 1.10Example of a lipid molecular structure

20 1 Overview of Biophotonics
1.6.2 Biological Cells
All organisms consist of two structurally different kinds of cells called prokaryotic
cells and eukaryotic cells.Prokaryotic cellshave few internal structures and no true
cell nucleus. These cells are found only in bacteria, with the smallest cells being
0.1–1lm in diameter. Most bacteria are 1–10lm in diameter.Eukaryotic cellsare
found in all animals, plants, fungi, and protists (one-celled eukaryotic organisms
that are not fungi, plant, or animals, e.g., algae and amoebas). As is shown in
Fig.1.11, eukaryotic cells are typically 10–100lm in diameter and have a true
nucleus that is surrounded by a membranous envelope. The nucleus averages 5lm
in diameter and contains most of the genes that control the cell. The entire region
between the nucleus and the surrounding membrane is called thecytoplasm. The
cytoplasm contains a semiﬂuid medium in which are suspended various subcellular
structures calledorganelles. Table1.8gives a summary of the various key orga-
nelles and their functions in a eukaryotic cell.
1.6.3 Mitochondria
Mitochondria are specialized organelles that are found in large numbers in most
cells. Their main functions are in the chemical processes of respiration and energy
production. The mitochondrion organelle has a double membrane with the inner
layer being folded inward to form layers, as Fig.1.12shows. Because these
organelles play a key role in energy production and are involved in many cellular
disorders, the resulting cellular variations that can occur from the interaction of
mitochondria with light is of high interest in biophotonics [33–35]. A number of
examples of these interactions and their effects on biological tissues are discussed in
various chapters of this book.
Golgi apparatus
Nucleus
(5 μm diameter)
Nucleolus
Nucleoplasm
Mitochondrion
Ribosome
Microtubules
Lysosome
Rough ER
Smooth ER
Cytoplasm
Cell membrane
Cell size
10-100 μm
Peroxisome
Fig. 1.11Major constituents of a eukaryotic cell

1.6 Structures of Biological Cells and Tissues 21
Table 1.8Summary of the various key organelles and their functions in a eukaryotic cell
General function Organelle anditsfunctions
Genetic control Chromosomesin the nucleus: serve as the location for
inherited DNA, which program the synthesisof proteins
Nucleolusinthe nucleus: produce ribosomes
Production of macromoleculesRibosomes: responsible for synthesis of polypeptides
Rough endoplasmic reticulum(ER): assist in protein
synthesisand membraneproduction
Smooth ER: synthesize lipids; store and release calcium
ions in muscle cells; handle liver cell functions
Golgi apparatus: handle chemical products of the cell
Maintenance of the cell Lysosomes: digest food and other materials
Peroxisomes: metabolize lipids andcarbohydrates;
handleenzymatic disposal of hydrogen peroxide
Energy processing Mitochondria: responsible for cellular respiration and
synthesis ofadenosine triphosphate(ATP)
Support, movement, and
communication between cells
Cytoskeleton: a microscopic network ofproteinﬁlaments
and microtubulesthat maintains cell shape, anchors
organelles, moves cells and organelles within cells
Glycocalyx: protects surfaces; binds cells in tissues
Intercellular junctions: handle communication between
cells; bind cells in tissues
Fig. 1.12Cross-sectional
view of thestructureof a
mitochondrion
Folded
matrix
Outer membrane
Inner membrane
1.6.4 Biological Tissues and Organs
Abiological tissue(or simply atissue) is an ensemble of similar cells that col-
lectively carry out a speciﬁc function. The four basic categories are epithelial,
connective, muscle, and nervous tissues. The characteristics of these tissues are
described in the following paragraphs and are summarized in Table1.9.
Epithel issuescover the outside surface of the skin and line the inner surfaces
of organs and cavities within the body. The cells of an epithelium are connected by
tight junctions and thus serve as a barrier to protect against mechanical injury,
invading microorganisms, andﬂuid loss. In addition to protecting the organs that
they cover or line, some epithelial tissues are specialized for absorbing or secreting

chemical solutions. One example is the mucous membrane, which secretes a slip-
pery substance called the mucous that lubricates and moistens a speciﬁc tissue
surface.
22 1 Overview of Biophotonics
The functions ofconnective tissueare to bind together other tissues, to give
shape to organs, and to holdthe
organs in place. Examples of connective tissue are
loose connective tissue, adipose tissue,ﬁbrous connective tissue, cartilage, bone,
and blood.Loose connective tissueconsists of a loose weave of proteinﬁbers,
which are categorized as collagenousﬁbers (a rope-like coil of three collagen
molecules that resist stretching), elasticﬁbers (rubbery stretchableﬁbers made of
elastin that quickly restore skin shape if it is stretched),ﬁbroblasts (cells that
maintain the structural integrity of connective tissue), and microphages (travelling
cells that swallow bacteria and the debris of dead cells and eliminate them from the
body).Adipose tissueis located beneath the skin, around internal organs, and in
bone marrow. Its functions include providing insulation from heat and cold, pro-
viding a protective padding around organs, and storing lipids that can be used to
meet the energy needs of the body.Fibrous connective tissueare dense
collagen-enrichedﬁber bundles that have a high tensile strength in order to attach
muscles to bones (tendons) and to hold bones together at their joints (ligaments).
Cartilageis a strong but yetﬂexible support material consisting of collagenous
ﬁbers and a protein-carbohydrate complex called chondrin. Cartilage provides
support in locations such as the nose, the ears, the rings that reinforce the windpipe,
and the cushioning discs between vertebrae.Boneis a combination of mineralized
connective tissue andﬂexible collagen that supports the body of most vertebrates.
The interior of bones contains a spongy tissue calledmarrow.Bloodis categorized
as a connective tissue because, like other connective tissues, it has an extensive
extracellular matrix. This matrix is in the form of a liquid calledplasma. This liquid
has red blood cells, white blood cells, and platelets suspended in it. Red blood cells
Table 1.9Characteristics and functions of basic biological tissues
Biological
tissue
Characteristic Functions
Epithelial
tissue
Cover outside skin surfaces; line inner
surfaces of organs and cavities in the
body
Protect against
invading
microorganisms,ﬂuid loss,
and
mechanical injury
Absorb or secrete special
chemical solutions
Connective
tissue
Examples: loose andﬁbrous
connective tissue, adipose tissue,
cartilage, bone, blood
Bind together various tissues, give
shape to organs, and hold organs in
place
Muscle
tissue
Long, excitable cells capable of
considerable contraction
The three main types are skeletal,
cardiac, and visceral muscles
Nervous
tissue
Cells that make up the central and
peripheral nervous systems
C
ystem: brain and
spinal cord
Peripheral nervous system: cranial
and spinal nerves

carry oxygen throughout the body, white blood cells act against invaders such as
bacteria and viruses, and platelets are involved in the clotting of blood.
1.7 Summary 23
Muscle tissueis composed of long, excitablecell s that are capable of consid-
erable contraction. The three main types are skeletal muscles (which are responsible
for voluntary movements of the body), cardiac muscles (which form the contractile
walls of the heart), and visceral muscles (which are in the walls of the digestive
tract, bladder, arteries, and other internal organs).
Nervous tissuesare the cells that make up the central and the peripheral nervous
systems. The neural tissue in the central nervous system forms the brain and spinal
cord. In the peripheral nervous system, the neural tissue forms the cranial nerves
and spinal nerves.
In humans and most animals, a number of specialized functional units called
organsare composed of multiple layers of different types of biological tissues. In
the human body there are over 70 organs that have various sizes and functions.
Some of the major organs include the bladder, brain, eyes, heart, kidneys, liver,
lungs, skin, spleen, stomach, and thyroid. As an example of layers and their
functions, the human stomach consists of an arrangement of four tissue layers. From
the inner to the outer layer these are a thick epithelium that secrets mucous and
digestive juices, a layer of connective tissue followed by a layer of smooth muscle,
andﬁnally another layer of connective tissue. A collection of certain organs that
carry out a speciﬁc function is called anorgan system. These include the digestive,
cardiovascular, muscular, skeletal, nervous, respiratory, endocrine, and lymphatic
systems.
1.7 Summary
The discipline of biophotonics deals with the interaction between light and bio-
logical matter. The techniques and tools used in this discipline have become
indispensable for basic life sciences research and for biomedical diagnosis, therapy,
monitoring, and surgery. Among the diverse applications are biomedical imaging
techniques, microscopic and spectroscopic procedures, endoscopy, tissue pathol-
ogy, bloodﬂow monitoring, light therapy, biosensing, laser surgery, dentistry, and
health status monitoring.
This c
ﬁr st describes the concepts and beneﬁts of biophotonics, gives
illustrations of the disciplines where biophotonic techniques are used, and gives
some basic concepts of light-tissue interactions. Further details of light-tissue
interactions are given in Chap.6. In order to understand the various biophotonic
concepts and their application to medical issues, theﬁnal section of this chapter
gives a brief tutorial of biological cell and molecular structures, cellular and
molecular functions, and the vocabulary used to describe these structures and
functions.

Problems
ﬁ
24 1 Overview of Biophotonics
1:1If a biological tissue sample has a refractive index n = 1.34, show that the
speed of light in this medium is s = 2.24
10
8
m/s = 22.4 cm/ps.
1:2Show that the photon energies for UV-C light at 190 nm and UV-A light at
315 nm are 6.53 and 3.94 eV, respectively.
1:3Elastin is a protein consisting of tissueﬁbers that can stretch to several times
their normal length and then return to their original conﬁguration when the
stretching tension is released. (a) Using library or Web resources, what are the
four basic amino acids found in elastin? (b) Give at least four organs in the
human body that contain elastin and brieﬂy describe its function in these
organs.
1:4When ATP is broken down (hydrolyzed) the energy that is released is used for
many metabolic processes. (a) Using Web resources, draw the chemical
structure of the nucleotide ATP to show the triple phosphate group, the sugar
molecule, and the nitrogen base. (b) Describe how ATP releases energy by
producing adenosine diphosphate (ADP) or adenosine monophosphate (AMP).
(c) What happens to these molecules when an orgasm is resting and does not
need energy immediately?
1:5For certain biophotonic procedures, an important factor is the ratio of the
surface area of a cell to its volume. Consider two different spherical cells called
Cell #1 and Cell #2. Suppose Cell #1 has a membrane surface area of 1lm
2
for every microliter (lL) of volume. If the diameter of Cell #2 isﬁve times
smaller than the diameter of Cell #1, show that the ratio of the surface area to
the volume for Cell #2 is 5lm
2
/lL.
1:6Suppose the body of a 70-kg adult human male contains about 44 billion cells.
If the average mass density of humans is about the same as that of water
(1 gm/cm
3
), show that the average volume of a human cell is about 1.59ﬁ10
6
lm
3
.
1:7A product data sheet for a certain photodetector states that a−32 dBm optical
power level is needed at the photodetector to satisfy a speciﬁc performance
requirement. Show that the required power level in nW (nanowatt) units is
631 nW.
References
1.N.H. Niemz,Laser-Tissue Interaction, 4th ed. (Springer, 2019)
2.L.V. Wang, H.I. Wu,Biomedical Optics:
Principles and
Imaging(Wiley, 2007)
3.X. Zhao, M. Lu (eds.),Nanophotonics in Biomedical Engineering(Springer, 2021)
4. J. Popp, V.V. Tuchin, A. Chiou, S.H. Heinemann (eds.),Handbook of Biophotonics: Vol. 1:
Basics and Techniques(Wiley, 2011)
5. J. Popp, V.V. Tuchin, A. Chiou, S.H. Heinemann (eds.),Handbook of Biophotonics: Vol. 2:
Photonics for Healthcare(Wiley, 2011)
6.A.J. W
.J. C. van Gemert (eds.),Optical-Thermal Response of Laser-Irradiated Tissue,
2nd ed. (Springer, 2011)

References 25
7.S.L. Jacques, Optical properties of biological tissues: a review. Phys. Med. Biol.58, R37–R61
(2013)
8.T. Vo-Dinh (ed.),Biomedical Photonics Handbook, vol. I–III, 2nd ed. (CRC Press, 2014)
9.W.F. Cheong, S.A. Prahl, A.J. Welch, A review of the optical properties of biological tissues.
IEEE J. Quant. Electron.26(12), 2166–2185 (1990)
10.K. Tsia,Understanding Biophotonics(Pan Stanford Publishing, 2015)
11.M. Olivo, U.S. Dinish (eds.),Frontiers in Biophotonics for Translational Medicine(Springer,
2016)
12.A.H.-P. Ho, D. Kim, M.G. Somekh (eds.),Handbookof
Photonics for Biomedical
Engineering(Springer, 2016)
13.F.J. Kao, G. Keiser, A. Gogoi (eds.),Advanced Optical Methods for Brain Imaging(Springer,
2019)
14.Z. Li, H. Marks, C.L. Evans, G. Apiou-Sbirlea. Sensing, monitoring, and release of
therapeutics: the translational journey of next generation bandages. J. Biomed. Opt.24(2),
article 021201 (2019)
15.S. Roointan, P. Tavakolian, K.S. Sivagurunathan, A. Mandelis, S.H. Abrams, Detection and
monitoring of early dental caries and erosion using three-dimensional enhanced
truncated-correlation photothermal coherence tomography imaging. J. Biomed. Opt.26(4),
article 046004 (2021)
16. I. Hussain, A.K. Bowden, Smartphone-based optical spectroscopic platforms for biomedical
applications: a review. Biomed. Opt. Express12(4), 1974–1998 (2021)
17. J.T. Collins et al., Robotic microscopy for everyone: the OpenFlexure microscope. Biomed.
Opt. Express11(5), 2447–2460 (2020)
18.M. Pisco, A. Cusano, Lab-on-ﬁber technology: a roadmap toward multifunctional plug and
play platforms (Review). Sensors20(17), article 4705 (2020)
19.V.Y Zaitsev, A.L. Matveyev, L.A. Matveev, A.A. Soversky, M.S. Hepburn, A. Mowla, B.F.
Kennedy, Strain and elasticity imaging in compression optical coherence elastography: the
two-decade perspective and recent advances. J. Biophotonics14(2), article e202000257
(2021)
20. J. Albert, A lab onﬁber. IEEE Spectr.51,48–53 (2014)
21.S.P. Morgan, B.C. Wilson, A. Vitkin, F.R.A. J. Rose,Optical Techniques in Regenerative
Medicine(CRC Press, 2014)
22.S.A. Boppart, R. Richards-Kortum, Point-of-care and point-of-procedure optical imaging
technologies for primary care and global health (Review article). Sci. Transl. Med.6(253),
article 253rv2 (2014)
23.L. Ma, B. Fei, Comprehensive review of surgical microscopes: technology development and
medical applications. J. Biomed. Opt.26(1), article 010901 (2021)
24.B.J.-F. Wong, J. Ligner,Biomedical Optics in Otorhinolaryngology(Springer, 2016)
25.B.E.A. Saleh, M.C. Teich,Fundamentals of Photonics, 3rd ed. (Wiley, 2019)
26.F.L. Pedrotti, L.M. Pedrotti, L.S. Pedrotti,Introduction to Optics, 3rd ed. (Cambridge, 2017)
27.G. Keiser,Fiber Optic Communications(Springer, 2021)
28.E. Hecht,Optics, 5th ed. (Pearson, 2016)
29.G. Karp, J. Iwasa, W. Marshall,Karp’sCell and Molecular Biology, 8th ed. (Wiley, 2019)
30.A.K. Nayak, A.K. Dhara, D. Pal,Biological Macromolecules(Academic, 2021)
31.H. Lodish, A. Berk, C.A. Kaiser, M. Krieger, A. Bretscher, H. Ploegh, K.C. Martin, M. Yaffe,
A. Amon,Molecular Cell Biology, 9th ed. (Macmillan, 2021)
32.L.A. Urry, M.L. Cain, S.A. Wasserman, P.V. Minorsky, R.B. Orr,Campbell Biology, 12th ed.
(Pearson,2021)
33.S.Y. C
.Y. Lee, P.S. Chung, S. Kim, B. Choi, M.W. Suh, C.K. Rhee, J.Y. Jung,
Enhanced mitochondrial membrane potential and ATP synthesis by photobiomodulation
increases viability of the auditory cell line after gentamicin-induced intrinsic apoptosis. Sci.
Reports9, article 19248 (2019)

26 1 Overview of Biophotonics
34. J.X. Tao, W.C. Zhou, X.G. Zhu, Mitochondria as potential targets and initiators of the blue
lighthazard
to the
retina: review. Oxidative Med. Cell. Longev.2019, article 6435364 (2019)
35.A.S.C. F
.W. Soong, T.T. Yeo, K.L. Lim, Mitochondrial dysfunction and Parkinson’s
disease—near-infrared photobiomodulation as a potential therapeutic strategy. Front. Aging
Neurosci.12, article 89 (2020)

2
Basic Principles of Light
Abstract
The purpose of this chapter is to present an overview of the fundamental
behavior of light. Having a good grasp of the basic principles of light is
important for understanding how light interacts with biological matter, which is
the basis of biophotonics. A challenging aspect of applying light to biological
materials is that the optical properties of the materials generally vary with the
light wavelength and can depend on factors such as the optical power per area
irradiated, the temperature, the light exposure time, and light polarization. The
following topics are included in this chapter: the characteristics of lightwaves,
polarization, quantization and photon energy, reﬂection and refraction, and the
concepts of interference and coherence.
Knowing the basic principles of light is important for understanding how light
interacts with biological matter, which is the basis of biophotonics. As Chap.6
describes, light impinging on a biological tissue can pass through or be absorbed,
reﬂected, or scattered in the material. The degree of these interactions of light with
tissue depends signiﬁcantly on the characteristics of the light and on the optical
properties of the tissue. A challenging aspect of applying light to biological
materials is the fact that the optical properties of the material generally vary with the
light wavelength. In addition, the optical properties of tissue can depend on factors
such as the optical power per area irradiated, the temperature, the light exposure
time, and light polarization. Chapter6and subsequent chapters present further
details on these light-tissue interaction effects.
The purpose of this chapter is to present an overview of the fundamental
behavior of light [1–10]. Note that this chapter is not intended as a comprehensive
review of the principles of optics. It merely serves as an introduction to the basic
characteristics of light to help understand light-tissue interactions related to bio-
photonics. The behavior of light can be explained through the theory of quantum
optics, which describes light as having properties of both waves and particles. This
©The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2022
G. Keiser,Biophotonics, Graduate Texts in Physics,
https://doi.org/10.1007/978-981-19-3482-7_2
27

phenomenon is called thewave-particle duality. The dual wave-particle picture
describes the transportation of optical energy either by means of the classical
electromagnetic wave concept of light or by means of quantized energy units or
photons. The wave theory can be employed to understand fundamental optical
concepts such as reﬂection, refraction, dispersion, absorption, luminescence,
diffraction, birefringence, and scattering. However, the particle theory is needed to
explain the processes of photon generation and absorption.
28 2 Basic Principles of Light
The following topics are includedinthis chapter: the characteristics of light-
waves, polarization, quantization and photon energy, reﬂection and refraction, and
the concepts of interference and coherence.
2.1 Lightwave Characteristics
The theory of classical electrodynamics describes light as electromagnetic waves
that are transverse, that is, the wave motion is perpendicular to the direction in
which the wave travels. In thiswave opticsorphysical opticsviewpoint, a series of
successive spherical wave fronts (referred to as atrain of waves) spaced at regular
intervals called awavelengthcan represent the electromagnetic waves radiated by a
small optical source with the source at the center as shown in Fig.2.1a. Awave
frontis deﬁned as the locus of all points in the wave train that have the same phase
(the termphaseindicates the current position of a wave relative to a reference
point). Generally, one draws wave fronts passing through either the maxima or the
minima of the wave, such as the peak or trough of a sine wave, for example. The
wave fronts (also calledphase fronts) therefore are separated by one wavelength.
When the wavelength of the light is much smaller than the object (or opening)
that it encounters, the wave fronts appear as straight lines to this object or opening.
In this case, the lightwave can be represented as a plane wave and a light ray can
(a) (b)
Fig. 2.1Representations ofaspherical waves radiating from a point source andbplane waves
and their associated rays

Amplitude A
Fig. 2.2A monochromatic
indicate its direction of travel, that is, the ray is drawn perpendicular to the phase
front, as shown in Fig.2.1b. The light-ray concept allows large-scale optical effects
such as reﬂection and refraction to be analyzed by the simple geometrical process of
ray tracing. This view of optics is referred to asray opticsorgeometrical optics.
The concept of light rays is very useful because the rays show the direction of
energyﬂow in the light beam.
2.1 Lightwave Characteristics 29
Tohelpunderstandwaveoptics,this sectionﬁrst discusses some fundamental
characteristics of waveforms. For mathematical convenience in describing the char-
acteristics of light,ﬁrst it is assumed that the light comes from an ideal monochro-
matic (single-wavelength) source with the emitted lightwave being represented in the
time domain by an inﬁnitely long, single-frequency sinusoidal wave, as Fig.2.2
shows. In a real lightwave or in an optical pulse ofﬁnite time duration, the waveform
has an arbitrary time dependence and thus is polychromatic. However, although the
waveform describing a polychromatic wave is nonharmonic in time, it may be
represented by a superposition of monochromatic harmonic functions.
2.1.1 Monochromatic Waves
A monochromatic lightwave can be represented by the following real waveform u
(r, t) that varies harmonically in time
uðr;t)¼AðrÞcos½xtþuðr? ð2:1Þ
whereris a position vector so that
AðrÞ is the wave amplitude at positionr
uðrÞ is the phase of the wave at positionr
x¼2pm is the angular frequency measured in radians/s or s
−1
k is the wavelength of the wave
m¼c=k is the lightwave frequency measured in cycles/s or Hz
T¼1=m¼2p=xis the wave period in units of seconds
wave consistsof a sine wave
of inﬁnite extent with
amplitude A, wavelengthk,
and period T
Wavelength
or period T
Distance or time

The waveform also can be expressed by the following complex function
tude of the wave and exp x = e
x
is the exponential function. The waveform u(r,t)is
the real part of U(r,t)
ð
i
Example 2.1
Consider a spherical wave given by
30 2 Basic Principles of Light
Uðr;t)¼AðrÞexpfi½xtþuðr?g ?UðrÞexpðixtÞ¼UðrÞe
ixt
ð2:2Þ
where the time-independent factorUðrÞ¼AðrÞexp½iðr?is the complex ampli-u
u(r;t)¼RefUðr;t)g¼
1
2
Uðr;t)þU
〉
ðr;tÞ? 2:3Þ
where the symbol * denotes the complex conjugate.
Theoptical intensityI(r, t), which is deﬁned as the optical power per unit area
(for example, in units such as W/cm
2
or mW/mm
2
), is equal to the average of the
squared wavefunction. That is, by letting the operation〈x〉denote the average of a
generic function x, then
Iðr;t)¼U
2
ðr;tÞ
〈〉
¼jUðrÞj
2
1þcosð2½2pmtþuðr??h ð2:4Þ
When this average is taken over a time longer than the optical wave period T, the
average of the cosine function goes to zero so that the optical intensity of a
monochromatic wave becomes
IðrÞ¼jUðrÞj
2
ð2:5Þ
This shows that the intensity of a monochromatic wave is independent of time
and is the square of the absolute value of its complex amplitude.
UðrÞ¼
A
0
r
expði2pr=kÞ
1=2
whereA 0¼1:5W is a constant and r is measured in cm. What is the
intensity of this wave
?
Solution: From Eq. (2.5), using the condition thatje
ix
j
2
¼½e
ix
e
þix
?1,
then
IðrÞ¼jUðrÞj
2
¼ðA 0=rÞ
2
¼ð1:5W
1=2
Þ=r(in cm)
hi
2
¼2:25=r
2
ðin W=cm
2
Þ

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man should have an absolute empire over my destiny. One can see
how my character was shaping, the turn my ideas were taking, the
first attacks of my genius; for I can speak of that genius as a malady,
whatever it may have been, rare or vulgar, worthy or unworthy of the
name I give it for want of a word wherewith to express myself. Had I
been more like the rest of mankind, I should have been happier: any
one who could have succeeded, without depriving me of my
intelligence, in killing what is called my talent would have treated me
as a friend.
When the Comte de Boisteilleul took me to M. d'Hector, I heard old
and young sailors discuss their campaigns and talk of the countries
they had visited: one had returned from India, another from America;
this one was to set sail to go round the world, the other was about to
join the Mediterranean station, to visit the shores of Greece. My uncle
pointed out La Pérouse
[146]
to me in the crowd, a new Cook, the
manner of whose death has remained the secret of the tempests. I
listened to everything, I looked at everything, without uttering a
word; but there was no sleep for me that night: I spent it, in
imagination, in delivering combats or discovering unknown lands.
Be that as it may, on seeing Gesril return to his parents, I thought
that there was nothing to prevent me from going home to my own. I
should have much liked the naval service, if my spirit of independence
had not disinclined me to service of any kind: I was born with an
incapacity for obedience. Voyages tempted me, but I felt that I should
enjoy them only in solitude, left free to follow my own will. At last,
giving my first proof of fickleness, without telling my uncle Ravenel,
without writing to my parents, without asking permission of anybody,
without waiting for my cadet's commission, I left one morning for
Combourg, where I dropped as though from the clouds.
I am to this day astonished to think how, in view of the terror with
which my father inspired me, I could have dared to take such a
resolve; and what is quite as astonishing is the manner in which I was
welcomed. I had every reason to expect transports of the most
furious anger, and I was gently received. My father was content to
shake his head, as though to say, "Here's a pretty trick!" My mother

embraced me with all her heart, grumbling the while, and my Lucile
kissed me in an ecstasy of joy.
[75] This book was written at Dieppe in September and October
1812 and at the Vallée-aux-Loups in December 1813 and January
1814, and was revised in June 1846.—T.
[76] The author's forty-fourth birthday.—B.
[77] Étienne Denis Duc Pasquier (1767-1862), became Prefect of
Police under Bonaparte in 1810, President of the Chamber of
Deputies under Louis XVIII. in 1816, Foreign Minister in 1819. In
1821, on the fall of the Villèle Ministry, Pasquier received his
peerage. Louis-Philippe made him President of the Chamber of
Peers in 1830, Chancellor in 1837, and created him a duke in 1844.
In his capacity as a peer, therefore, and also as an Academician, he
eventually became Chateaubriand's colleague.—T.
[78] The River Arques, which discharges itself at Dieppe, was
formerly called the Deep.—T.
[79] Abraham Marquis Duquesne (1610-1688), the famous sailor.
His religion—he was a Huguenot—prevented Louis XIV. from
making him an admiral; the highest rank he obtained was that of
lieutenant-general. A statue of Duquesne was erected at Dieppe in
1844.—T.
[80] Robert Wace, a native of Jersey, author of the Brut
d'Angleterre or Artus de Bretagne, the Roman du Rou (Rollo Duke
of Normandy), and the Chronique ascendante des ducs de
Normandie. He was reading-clerk to Henry I. and Henry II., later a
canon of Bayeux, and died in England circa 1184.—T.
[81] Pliny, III. X. 15.—T.
[82] Urbain René de Hercé (1726-1795), consecrated Bishop of Dol
in 1757, was shot not at, but after, Quiberon, at Vannes, 28 July
1795, together with Sombreuil and fourteen other victims,
including his brother, François de Hercé (1733-1795), Grand-Vicar
of Dol, and Gesril (vide supra).—B.
[83] Étienne Bezout (1730-1783), author of a number of
mathematical works employed in schools in the eighteenth century.
—T.
[84] Charles Dufresne Ducange (1610-1688), a learned expert in
historical research, author of the Glossarium mediæ et infimœ

Latinitatis, in which the description of the quintain occurs, and a
number of other works of value.—T.
[85] The Manuscript of 1826 here contains a short description of
the sport of the quintain: "All the bridegrooms of the year within
the holding of Combourg were obliged, in the month of May, to
come and break a wooden lance against a post placed in a sunk
road that ran above the Great Mall. The tilters were on horseback;
the bailiff, who acted as lord of the lists, examined the lance, and
declared that there was no fraud nor guile in the arms: it was
allowed to tilt three times at the post, but at the third time, if the
lance was not broken, the jibers of the rustic tournament covered
the awkward tilter with pleasantries, who paid a crown-piece to the
liege lord."—T.
[86] Noble Maître François Jean Baptiste Potelet, Seigneur de
Saint-Mahé et de La Durantais.—B.
[87] Gilles Marie de Launay, Sieur de La Billardière, successively
procurator-fiscal of Bécherel, sénéchal des juridictions of the
Vauruffier, the Viscounty of Besso and the Marquisate of Caradenc,
and bonder of the King's tobacco taxes at Combourg.—B.
[88] I have met my friend David again since: I shall tell when and
how.—Author's Note (Geneva, 1832).
[89] Jean Baptiste Gesbert, Seigneur de La Noé-Sécho, seneschal
of the manorial jurisdiction of Combourg.—B.
[90] Maître René Petit, procurator-fiscal of the County of
Combourg.—B.
[91] Maître Julien Corvaisier or Le Corvaisier, notary and attorney
of the jurisdiction.—B.
[92] The Abbé Jean François Chalmel, chaplain of Combourg
Castle.—B.
[93] Jean Anne Pinot du Petitbois (1737-1789) lived in the Château
du Grandval at Combourg, still occupied by his descendants.—B.
[94] Michel Charles Locquet, Comte de Château-d'Assis, lived in the
Château de Triaudin, Combourg, now owned by the Vicomte Roger
du Petitbois.—B.
[95] Nicolas Pierre Philippes, Seigneur de Trémaudan.—B.
[96] René Malo Sévin, rector of the parish of Combourg in 1776,
refused to subscribe to the civil constitution of the clergy, and went

to Jersey in 1792. He returned in 1797, was reinstated in his parish
in 1803, and died at Combourg in 1817.—B.
[97] Claude Anne, successively Vicomte, Marquis, and Duc de
Saint-Simon, emigrated to Spain, entered the Spanish service, and
became Captain-General of Old Castile. King Charles IV. created
him a grandee of Spain, King Ferdinand VII. a duke. He died in
Madrid in 1819. In 1808, on the capture of Madrid by the French,
he was sentenced to death by court-martial; the sentence was
commuted to imprisonment for life, and he was confined in the
Citadel of Besançon until the fall of the Empire in 1814.—B.
[98] It gave me a genuine pleasure to renew my acquaintance,
during the Restoration, with this gallant officer, so distinguished for
his loyalty and his Christian virtues.—Author's Note (Geneva, 1831).
Jacques Vincent Marquis de Causans de Mauléon (1751-1824), was
promoted to the rank of lieutenant-general in 1814, and sat in the
Chamber of Deputies as member for Vaucluse from 1815 until his
death.—B.
[99] Antoine Louis Marquis de Wignacourt, Knight of St. Louis.—B.
[100] François Placide Maillard, Seigneur de La Morandais. The
Maillards de La Morandais delivered proofs of eight generations of
nobility in 1670. Those who had settled at Combourg had
degenerated through poverty.—B.
[101] Guillaume de Lamoignon (1617-1677), First President of the
Parliament of Paris, founder of a most distinguished legal family,
and great-grandfather of Lamoignon de Malesherbes.—T.
[102] "Right gladly and in brave array,
By wood and river made his way:
For no folk through the woods advance
Right gladly like the folk of France." —T.
[103] Armand Louis de Gontaut de Biron, Duc de Lauzun (1747-
1793), and Duc de Biron on the death of his father in 1788. He was
one of the handsomest men at the Court of Louis XVI. In 1789 he
joined the party of the Duc d'Orléans, and served as a general in
the Republican army, but was guillotined on the last day of
December 1793.—T.
[104] Prince Eugène de Savoie-Carignan (1753-1785), younger son
of Prince Louis Victor de Savoie-Carignan, and brother of the
Princesse de Lamballe. A scion of the younger branch of the Royal
House of Savoy, he entered the French service under the title of
Count of Villafranca, and was made colonel of the Villefranche

Regiment. In 1781 he married Elizabeth Anne, daughter of Jean
François Nicolas Magon, Seigneur de Boisgarein; but the marriage
was annulled by parliament upon the petition of the Prince's
parents. He struggled desperately to obtain a revision of the decree
of annulment. On the accession of the younger branch to the
throne of Sardinia in 1831, the grandson of Prince Eugène and
Mademoiselle de Boisgarein was restored to his ancestral rank, and
in 1888 his morganatic children received from the late King of Italy
the name of Villafranca-Soisson, with the title of count.—B.
[105] Pierre Louis Lacretelle (1751-1824), known as Lacretelle the
Elder, to distinguish him from his brother, Charles Joseph Lacretelle,
the Younger. He was a member of the French Academy, and author
of a number of legal works and political and philosophical treatises.
—T.
[106] Florio's MONTAIGNE, Booke I. chap. 9: Of Lyers.—T.
[107] By Diderot; printed in 1738, and first performed at the
Comédie Française ten years after, when it met with indifferent
success, attaining a total of seven performances.—B.
[108] 11 January 1780, Marie Anne Françoise married Jean Joseph
Geffelot, Comte de Marigny; Bénigne Jeanne married Jean François
Xavier Comte de Québriac, Seigneur de Patrion.—B.
[109] LUCRETIUS, I. i.—T.
[110] TIBULLUS, I. i, 45.—T.
[111] Jean Baptiste Massillon (1663-1742), Bishop of Clermont,
and a famous Catholic preacher. He left nearly a hundred sermons,
in addition to a great number of other religious works. Massillon
was elected an Academician in 1789.—T.
[112] François Eudes de Mézeray (1610-1683). The Eudists,
founded by Jean Eudes, hare still a house at Rennes. The
community is also known as the Congregation of Jesus and Mary.—
T.
[113] STAT., Th., VII. 280.—T.
[114] SUET, Cæs. 39.—T.
[115] De Buonaparte et des Bourbons.—Author's Note (Geneva,
1831).
[116] Charles Hilaire de Chateaubriand (1708-1782), rector
successively of a number of country livings.—B.

[117] Louis Joseph (Louis V.) Prince de Condé (1736-1818), fourth
in descent from the Great Condé, and Commander-in-Chief of the
Army of the Emigrants, 1789-1800. At the Restoration, King Louis
XVIII. made his kinsman Grand-Master of the Household and
Colonel-General of the Infantry.—T.
[118] Louis Henri Joseph (Louis VI.) Duc de Bourbon (1756-1830),
son of Louis V. Prince de Condé and of the Princesse Louise
d'Orléans, and father of the unhappy Duc d'Enghien. The Duc de
Bourbon was found strangled-whether by his own hands or those
of his mistress, Madame de Feuchères, is uncertain—a few days
after the Revolution of 1830. He left the greater part of his large
fortune to the late Duc d'Aumale.—T.
[119] Part I. book I. chap. 7: De la communion.—T.
[120] "The bread I offer for your taking
Is that which the angels eat;
It is bread of God's own baking
From the first fruits of his wheat." —T.
[121] Charles Rollin (1661-1741), a famous French professor and
theologian.—T.
[122] The French Naval Guard (Garde marine) was a body of
nobles from which the naval officers were appointed.—T.
[123] The name of a celebrated Oratorian college, near Meaux,
suppressed by the Revolution of 1789.—T.
[124] Julien Louis Geoffroy (1743-1814), a distinguished dramatic
critic. He originated the literary feuilleton in the Journal des
Débats.—T.
[125] Pierre Louis Ginguené (1748-1815), Ambassador to Turin
under the Directory, and author of the Histoire littéraire d'Italie and
some poems, mostly imitated from the Italian.—T.
[126] The famous college on the Montagne Sainte-Généviève in
Paris, founded by Jean Hubert in 1430.—T.
[127] Évariste Désiré Desforges, Chevalier de Parny (1753-1814),
the author of a number of elegies and love-poems, which earned
for him the name of "the French Tibullus."—T.
[128] Rennes College was one of the most important in France. It
was founded by the Jesuits in 1607. When they left it, in 1762, a
communal college was established in the same buildings. These are
now occupied by the Lycée de Rennes, which, however, is greatly
diminished in size.—B.

[129] "Listen to the vows we offer,
O Terpsichore, Polyhymnia!
Reason herself her prayers doth proffer." —T.
[130] André François Jean du Rocher de Saint-Riveul (1772-1789),
son of Henri du Rocher, Comte de Saint-Riveul.—B. The Manuscript
of 1826 mentions that he was killed in the street at Rennes, as he
was going with his father to the Chamber of Nobles.—T.
[131] Jean Desmarets, advocate-general to the Parliament of Paris,
beheaded in 1382 for his failure to suppress the revolt of the
Maillotins.—T.
[132] Jean Victor Moreau (1763-1813), one of the greatest
generals of the Revolution, and the victor of the Battles of
Hochstädt and Hohenlinden. He subsequently entered into relations
with the Royalist Generals Pichegru and Cadoudal, was tried and
sentenced to two years' imprisonment, a sentence commuted to
exile in the United States. Here he received offers from the Tsar
Alexander to join the army of the Allies, which he eventually
accepted; but was killed by a cannon-ball immediately after
reaching the head-quarters of the Allied Army outside Dresden.—T.
[133] Joseph Pierre Picot de Limoëlan de Clorivière (1768-1826)
entered the army, espoused the Royalist cause, and refused to
accept the pacification of 1799. He returned to Paris, and was on
the eve of marrying a charming young lady of Versailles,
Mademoiselle Julie d'Albert, when the explosion of the infernal
machine took place in the Rue Saint-Nicaise (24 December 1799).
Limoëlan was one of the principal agents in the plot. Thanks to the
devotion of his betrothed, he escaped to America, and upon his
arrival in New York wrote to Mademoiselle d'Albert to come out to
him and be married there. The reply came as a shock to him.
Mademoiselle d'Albert had taken a vow to devote herself to God, if
her lover succeeded in making good his escape. She besought him
to forget the past and to think only of his eternal future. In 1808
the young officer entered the seminary at Baltimore. He
commenced a new life, changed his name to Clorivière, was
ordained priest in 1812, and received a curacy at Charleston. He
returned to France in 1815 to collect what remained of his fortune,
the whole of which he devoted to pious works in America, including
the re-endowment of the Convent of the Visitation at Georgetown,
founded by Miss Alice Lalor in 1805. Mademoiselle d'Albert survived
Father de Clorivière for many years. She kept her vow of celibacy,
but did not take the veil, for want of a vocation. At the age of fifty
she was relieved by Pope Gregory XVI. from her vow. She died at

Versailles, advanced in years, after a life devoted entirely to works
of piety and charity.—B.
[134] I omit a short anecdote.—T.
[135] Annibal Pierre François de Farcy de Montavallon. The
wedding took place in 1782.—B.
[136] Thérèse Josèphe de Moëlien (1759-1793), daughter of
Sébastien Marie Hyacinthe de Moëlien, Chevalier, Seigneur de
Trojolif (not Tronjoli), Kermoisan, Kerguelenet, &c. She was twenty-
three years of age when Chateaubriand saw her at Combourg, and
when writing his Memoirs he must have recalled her with his
school-boy eyes; for contemporary evidence declares that she was
not beautiful, nor even pretty. The words "and close friend of the
Marquis de La Rouërie" do not occur in the Manuscript of 1826.
Thérèse de Moëlien was in love, not with La Rouërie, but with
Major Chafner, an American officer, whom she was to have married
if she outlived the plot in which they were both engaged. She was
guillotined, however, in Paris on the 18th of June 1793. Major
Chafner was in London at the time of the discovery of the so-called
Breton Conspiracy. He returned to Brittany, and perished at Nantes,
after fighting on the side of the Vendeans to revenge the death of
Mademoiselle de Moëlien.—B.
[137] An allusion to the mystical hymns of Orpheus, which were
called "perfumes" (αρώματα).—B.
[138] Jean Baptiste Joseph Eugène de Ravenel du Boisteilleul
(1738-1815), first cousin of Chateaubriand's mother, and therefore
uncle in the manner of Brittany of the great writer.—B.
[139] Hyacinthe Eugène Pierre de Ravenel du Boisteilleul (1784-
1868), a captain of artillery, and decorated on the battle-field at
Smolensk, 17 August 1812.—B.
[140] Pauline Zoé Marie de Farcy de Montavallon (1784-1850)
married Hyacinthe de Ravenel du Boisteilleul, 16 November 1814.—
B.
[141] Vice-Admiral Charles Jean Comte d'Hector (1722-1808),
commander of the port of Brest from 1780 to 1791. He joined the
Princes' Army at Coblentz, and was made colonel of a regiment
consisting exclusively of naval officers. He died at Reading in
Berkshire at the age of eighty-six.—B.
[142] The Peace of Versailles, 1783.—T.

[143] Pierre André de Suffren-Saint-Tropez (1726-1788), known as
the Bailli de Suffren, had fought the English in India by sea and
land in the war of 1782.—T.
[144] Comte de Lamotte-Piquet (1720-1791), lieutenant-general of
the French Navy. Between 1737 and 1783 he took part in twenty-
eight campaigns, and distinguished himself especially in America.—
T.
[145] Charles Hector Comte d'Estaing (1720-1794), admiral in
command of the combined fleets at Cadiz on the signature of the
treaty of peace. He embraced the principles of the Revolution, and
served in the Republican army and naval forces; but was guillotined
in 1794.—T.
[146] Jean François Galaup, Comte de La Pérouse (1741-1788[?])
set out on a voyage of discovery in 1785. He was known to have
visited Japan and New Holland when, in 1788, all traces of him
were lost. In 1827, Captain Dillon discovered the wrecks of his
ships, the Boussole and the Astrolabe, off the coast of Vanikoro,
since called the Pérouse, one of the Santa Cruz group, between the
Solomon Islands and the New Hebrides.—T.
BOOK III
[147]
At Montboissier—Reminiscences of Combourg—Dinan College—
Broussais—I return home—Life at Combourg—Our days and evenings
—My donjon—Change from childhood to manhood—Lucile—Last lines
written at the Vallée-aux-Loups—Revelations concerning the mystery
of my life—A phantom of love—Two years of delirium—Occupations
and illusions—My autumn joys—Incantation—Temptation—Illness—I
fear and decline to enter the ecclesiastical state—A moment in my
native town—Recollection of Villeneuve and the tribulations of my
childhood—I am called back to Combourg—Last interview with my
father—I enter the service—I bid farewell to Combourg
Three years and six months have elapsed between the last date
attached to these Memoirs, Vallée-aux-Loups, January 1814, and the

date of today, Montboissier, July 1817. Did you hear the Empire fall?
No: nothing has disturbed the repose of this spot. Nevertheless the
Empire is lost; the immense ruin has crumbled in the course of my life
like Roman remains overturned in the bed of some unknown stream.
But events matter little to one who does not reckon them: a few years
escaping from the hands of the Eternal Father will do justice to all
these reports with an endless silence.
The previous chapter was written under the expiring tyranny of
Bonaparte and by the light of the last flashes of his glory: I am
commencing the present chapter under the reign of Louis XVIII. I
have been in close proximity to kings, and my political illusions have
vanished, as have the sweeter fancies of which I am continuing the
tale. Let me first say what makes me resume my pen: the human
heart is the toy of everything, nor can we foresee what trivial
circumstance will cause its joys and sorrows. Montaigne remarked
this: "There needeth no cause," he says, "to excite our minde. A
doating humour without body, without substance, overswayeth and
tosseth it up and down
[148]
."
I am now at Montboissier, on the borders of the Beauce and the
Perche
[149]
. The castle situated upon this property, belonging to
Madame la Comtesse de Colbert-Montboissier
[150]
, was sold and
demolished during the Revolution; only two pavilions remain, divided
by a railing, and formerly inhabited by the lodge-keeper. The park,
which is now laid out in the English style, retains some traces of its
former French symmetry: straight walks, copses set within hedges
give it a serious aspect; it has the attraction of a ruin.
Yesterday evening I was walking alone; the sky was like an autumn
sky; a cold wind blew at intervals. I stopped at an opening in a thicket
to look at the sun: it was sinking into the clouds above the tower of
Alluye, from which Gabrielle
[151]
, occupying that tower, saw the sun
set, as I did, two hundred years ago. What has become of Henry and
Gabrielle? The same that shall have become of me when these
Memoirs are published.

I was drawn from my reflections by the twittering of a thrush perched
on the topmost branch of a birch-tree. At once that magic sound
brought back before my eyes my father's domain: I forgot the
catastrophes which I had lately witnessed, and suddenly carried back
into the past, I saw once more the fields where I had so often heard
the thrush's song. When I listened to it then, I was sad, as I am
today; but that first sadness was of the kind which springs from a
vague longing for happiness, at a time when we are without
experience; the sadness which I now feel comes from the knowledge
of things appreciated and judged. The song of the bird in the
Combourg woods told me of a happiness which I hoped to achieve;
the same song in the park at Montboissier reminded me of days
wasted in the pursuit of that unattainable happiness. I have nothing
more to learn; I have travelled faster than others, and have made the
circuit of life. The hours fly and drag me with them; I have not even
the certainty of being able to complete these Memoirs. In how many
places have I already commenced to write them, and in what place
shall I finish them? How long shall I wander on the edge of the wood?
Let me make the most of the few moments left to me; let me hasten
to depict my youth, while I am still in touch with it: the traveller
quitting for ever an enchanted shore writes his journal in sight of the
land which is withdrawing, soon to disappear from sight.
I have described my return to Combourg and my reception by my
father, my mother, and my sister Lucile. The reader will perhaps
remember that my three other sisters were married and living on the
estates of their new families in the neighbourhood of Fougères. My
brother, whose ambition was beginning to display itself, was oftener in
Paris than at Rennes. He first bought a post as maître des requêtes,
which he sold in order to enter the military service. He entered the
Royal Cavalry Regiment; he then joined the diplomatic service, and
accompanied the Comte de La Luzerne to London, where he met
André Chénier
[152]
; he was on the point of obtaining the Vienna
Embassy, when our troubles broke out. He asked for Constantinople,
but found a formidable competitor in Mirabeau, who had been
promised this embassy as the price of his alliance with the Court

party. My brother had therefore almost taken leave of Combourg at
the time when I came to live there.
My father entrenched himself in his manor, which he never left, not
even to attend the sittings of the States
[153]
. My mother went to
Saint-Malo for six weeks in every year, at Eastertide; she looked
forward to that time as the period of her deliverance, for she detested
Combourg. A month before the journey, it was discussed as though it
were a hazardous enterprise; preparations were made; the horses
were rested. On the eve of departure, we went to bed at seven in the
evening, in order to get up at two o'clock in the morning. My mother,
to her great contentment, set out at three, and occupied the whole
day in covering twelve leagues.

I am sent to Dinan
College.
Lucile, who had been received as a canoness to the
Chapter of the Argentière, was about to be transferred to
that of Remiremont: while awaiting this change, she
remained buried in the country. As for myself, after my escapade from
Brest, I declared my wish to embrace the ecclesiastical state: the truth is
that I was only seeking to gain time, for I did not know what I wished. I
was sent to the college at Dinan to complete my humanities. I knew Latin
better than my masters; but I began to learn Hebrew. The Abbé de Rouillac
was the principal of the college, and the Abbé Duhamel my tutor.
Dinan, adorned with old trees, fortified with old towers, is built upon a
picturesque site, on a high hill at the foot of which flows the tidal Rance,
and overlooks sloping and pleasantly-wooded valleys. The mineral waters of
Dinan have some renown. This historic city, which gave birth to Duclos
[154]
,
displayed among its antiquities the heart of Du Guesclin: an heroic dust
which, stolen during the Revolution, was on the point of being pounded by
a glazier to be used for paint. Was it intended for pictures of victories won
over the enemies of the country?
M. Broussais, my fellow-townsman, became my fellow-student at Dinan.
The students were taken to bathe on Thursdays, like the clerks under Pope
Adrian I., or on Sundays, like the prisoners under the Emperor Honorius.
Once I was nearly drowned; on another occasion, M. Broussais was bitten
by ungrateful leeches, which failed to foresee the future
[155]
. Dinan was at
an equal distance from Combourg and Plancoët. I visited my uncle de
Bedée at Monchoix and my own family at Combourg by turns.
M. de Chateaubriand, who found it cheaper to keep me at home, my
mother, who wished me to persist in my religious vocation, but who would
have scrupled to urge me, no longer insisted upon my residence at college,
and I found myself imperceptibly settling down under the paternal roof.
I should take pleasure in recalling the habits of my parents even if they
were no more to me than a touching remembrance; but I reproduce them
the more readily in that the picture will appear as though traced from the
vignettes in mediæval manuscripts: centuries separate the present days
from those which I am about to depict.
*
On my return from Brest the gentry at Combourg Castle consisted of four:
my father, my mother, my sister, and me. A woman-cook, a waiting-maid,

Visitors to
Combourg.
two footmen and a coachman composed the whole household: two old
mares and a sporting-dog were huddled in a corner of the stable. These
twelve living beings were lost to sight in a manor-house where a hundred
knights, their ladies, squires, and varlets, and King Dagobert's chargers and
pack might almost have gone unnoticed.
All through the year, not a visitor presented himself at the castle, save a
few gentlemen, the Marquis de Montlouet
[156]
, the Comte de Goyon-
Beaufort
[157]
, who begged a night's lodging on their way to plead their
suits before the Parliament. They used to arrive in winter, on horseback,
with pistols in their saddle-bows, hunting-knives at their sides, and followed
by a servant, also on horseback, with a livery trunk behind him.
My father, always very ceremonious, received them
bareheaded on the steps, in the midst of the wind and
rain. Once inside the house, the country gentlemen
would talk of their Hanoverian campaigns, their family affairs, their law-
suits. At night they were conducted to the North Tower, to Queen
Christina's bed-chamber, a state-room containing a bed seven feet by
seven, hung with a double set of curtains in green muslin and crimson silk,
and held up by four gilt Cupids. The next morning, when I came down to
the great hall and looked out through the windows upon the country
covered with floods or hoar-frost, I saw nothing except two or three
travelers on the lonely embankment of the pond: it was our guests riding
away to Rennes.
These visitors did not know much about the things of life; nevertheless our
view was by their means extended a few miles beyond the horizon of our
woods. When they were gone, we were reduced on week-days to our family
circle, and on Sundays to the company of the village commoners and the
neighboring gentry.
On Sundays, in fine weather, my mother, Lucile, and I went to the parish
church across the Little Mall and along a country road; when it rained, we
went by the abominable Combourg High Street. We were not carried, like
the Abbé de Marolles
[158]
, in a light chariot drawn by four white horses,
captured from the Turks in Hungary. My father went but once a year to the
parish church to perform his Easter duties; the rest of the year he heard
Mass in the castle chapel. Seated in the pew of the lord of the manor, we
received the incense and the prayers in front of the black marble sepulchre

Life at Combourg
Castle.
of Renée de Rohan: a symbol of mortal honors; a few grains of incense
before a tomb!
Our Sunday diversions vanished with the day; they did not even recur
regularly. During the bad weather, entire months would pass and not a
single human being knock at the gate of our fortress. The sadness was
great that hung over the moors of Combourg, but greater still at the castle:
as one made his way beneath its vaultings, he experienced the same
feeling as on entering the Carthusian Monastery at Grenoble
[159]
. When I
visited the latter in 1805, I crossed a wilderness which increased in
desolation as I went; I thought it would end at the monastery, but I was
shown, within the very convent walls, the gardens of the Carthusian Friars
even more neglected than the woods. And at length, in the centre of the
monument, I found, shrouded in the folds of all this solitude, the former
graveyard of the community, a sanctuary from which eternal silence, the
genius of the place, spread its dominion over the mountains and forests
around.
The gloomy stillness of Combourg Castle was increased
by my father's taciturn and unsocial humour. Instead of
drawing his family and his retainers closer to him, he had
dispersed them to all the winds of the building. His bedroom was in the
small east tower, his study in the small west tower. The furniture of this
study consisted of three chairs in black leather and a table covered with
parchments and title-deeds. A genealogical tree of the Chateaubriand
family adorned the chimney-mantel, and in the embrasure of a window
hung arms of all sorts, from a pistol to a blunderbuss. My mother's room
extended over the great hall, between the two small towers; it had a
parqueted flooring and was adorned with faceted Venetian mirrors. My
sister occupied a closet leading out of my mother's room. The waiting-maid
slept far away, on the ground floor between the two great towers. Myself, I
was nestled in a sort of isolated cell at the top of the turret containing the
staircase which led from the inner yard to the different parts of the castle.
At the foot of this staircase, my father's valet and the other man-servant lay
in a vaulted basement, and the cook kept garrison in the great west tower.
My father rose at four o'clock in the morning, winter and summer alike: he
went to the inner yard to call and wake his valet at the entrance to the
turret staircase. A cup of coffee was brought to him at five; he then worked
in his study till midday. My mother and sister each breakfasted in her own

chamber at eight o'clock. I had no fixed time for rising or breakfasting; I
was supposed to study till noon: the greater part of the time I did nothing.
At half-past eleven, the bell rang for dinner, which was served at twelve.
The great hall did duty as both dining-room and drawing-room: we dined
and supped at one end, on the east side; when the meal was over, we went
and sat at the other end, the west side, before a huge chimney. The hall
was wainscoted, painted whity-grey, and adorned with old portraits ranging
from the reign of François I. to that of Louis XIV. Among these portraits one
recognized those of Condé and Turenne: a picture representing Achilles
slaying Hector beneath the walls of Troy hung over the chimney-piece.
After dinner we remained together until two o'clock. Then, if it was
summer, my father went fishing, visited his kitchen-gardens, walked within
the limits of the home park; in the autumn and winter he went shooting.
My mother withdrew to the chapel, where she spent some hours in prayer.
This chapel was a gloomy oratory, adorned with fine pictures by the
greatest masters, such as one would scarcely expect to find in a feudal
castle in the heart of Brittany. I still have in my possession a Holy Family by
Albani, painted on copper, which was taken from this chapel: it is all that
remains to me of Combourg. When my father had left the house and my
mother gone to her prayers, Lucile withdrew to her room and I either
returned to my cell or went out to roam about the country.
At eight o'clock the bell rang for supper. After supper, in fine weather, we
sat out on the steps. My father, armed with his gun, shot at the brown owls
which issued from the battlements at nightfall. My mother, Lucile and I
watched the sky, the woods, the dying rays of the sun, the rising stars. At
ten o'clock we went in and retired to bed.
The autumn and winter evenings were different. Supper over, the four of us
would leave the table and gather round the chimney. My mother flung
herself, with a sigh, upon an old couch covered in imitation Siam; a stand
was put before her with a candle. I sat down with Lucile by the fire; the
servants cleared the table and withdrew. My father then began a tramp
which lasted till he went to bed. He was dressed in a white ratteen gown,
or rather a kind of cloak, which I have seen no one wear except him. His
half-bald head was covered with a big white cap that stood straight up on
end. When he walked away to a distance from the fire-place, the huge hall
was so badly lighted by its solitary candle that he was no longer visible; we
could only hear him still walking in the darkness: then he would slowly

My lonely nights.
return towards the light and gradually emerge from the dusk, like a ghost,
with his white gown, his white cap, his long pale face. Lucile and I
exchanged a few words in a low voice when he was at the other end of the
hall; we hushed when he drew nearer to us. He asked, as he passed, "What
were you talking about?" Terror-stricken, we made no reply; he continued
his walk. For the rest of the evening, the ear heard nothing save the
measured sound of his steps, my mother's sighs, and the murmuring of the
wind
[160]
.
The hour of ten struck on the castle clock: my father stopped; the same
spring which had raised the hammer of the clock seemed to have arrested
his steps. He drew out his watch, wound it, took a great silver candle-stick
holding a tall candle, went for a moment to the small west tower, then
returned, candle in hand, and went towards his bedroom, which formed
part of the small east tower. Lucile and I placed ourselves on his way; we
kissed him and wished him good-night. He turned his dry, hollow cheek to
us without replying, continued his road, and withdrew inside the tower, the
doors of which we heard closing behind him.
The spell was broken: my mother, my sister and myself, who had been
changed into statues by my father's presence, recovered the functions of
life. The first effect of our disenchantment took the form of an overflow of
words: silence was made to pay us dear for having so long oppressed us.
When this torrent of words had sped, I called the waiting-woman and
escorted my mother and sister to their rooms. Before I went, they made me
look under the beds, up the chimneys, behind the doors, and inspect the
surrounding stairs, passages and corridors. All the traditions of the castle
concerning robbers and ghosts returned to their memory. The servants
were persuaded that a certain Comte de Combourg, with a wooden leg,
who had been dead three centuries, appeared at certain intervals, and that
he had been seen in the great staircase of the turret; sometimes also his
wooden leg walked alone, accompanied by a black cat.
These stories took up the whole of the time occupied by my mother and
sister in preparing for the night: they got into bed dying of fright; I climbed
to the top of my turret; the cook returned to the main tower, and the men
went down to their basement.
The window of my donjon opened upon the inner
courtyard; by day I had a view of the battlements of the
curtain opposite, where hart's-tongues grew and a wild

plum-tree. Some martins, which in summer buried themselves, screeching,
in the holes in the walls, were my sole companions. At night I could see
only a small strip of sky and a few stars. When the moon shone and sank in
the east, I knew it by the beams which struck my bed across the lozenged
window-panes. Owls, flitting from one tower to the other, passed and
passed again between the moon and me, outlining the mobile shadow of
their wings upon my curtains. Banished to the loneliest part, at the opening
of the galleries, I lost not a murmur of the darkness. Sometimes the wind
seemed to trip with light steps; sometimes it uttered wailings; suddenly my
door was violently shaken, groans issued from the basement, and then
these sounds would die away, only to commence anew. At four o'clock in
the morning, the voice of the master of the castle, calling the footman at
the entrance to the venerable vaults, made itself heard like the voice of the
last phantom of the night. This voice supplied for me the place of the sweet
harmony with the sound of which Montaigne's father was wont to awaken
his son
[161]
.
The Comte de Chateaubriand's stubbornness in making a child sleep alone
at the top of a tower might have had its inconvenience, but it turned out to
my advantage. This violent manner of treatment left me with the courage
of a man, without taking from me that vivid imagination of which it is
nowadays the tendency to deprive the young. Instead of seeking to
persuade me that ghosts did not exist, they obliged me to set them at
defiance. When my father asked me, with an ironical smile, "Is monsieur le
chevalier afraid?" he could have made me sleep with a corpse. When my
excellent mother said, "My child, nothing happens without God's leave; you
have nothing to fear from evil spirits so long as you remain a good
Christian," I was more reassured than by all the arguments of philosophy.
So complete was my success, that the night winds, in my uninhabited
tower, served but as playthings for my fancies and wings for my dreams.
My imagination, thus kindled, spread over every object, found nowhere
sufficient nourishment, and could have devoured heaven and earth. It is
this moral condition which it is now my task to describe. Immersed once
more in the days of my youth, I will try to grasp myself in the past, to
depict myself such as I was, such as perhaps I regret that I no longer am,
despite the torments which I then endured.
*
Scarcely had I returned from Brest to Combourg when a revolution took
place in my existence; the child vanished and there appeared the man, with

Lucile.
his joys which pass and his troubles which remain. At first all became
passion with me, pending the arrival of the passions themselves. When,
after a silent dinner, at which I had dared neither to eat nor speak, I
succeeded in escaping, my delight was incredible. I could not descend the
steps then and there: I should have flung myself headlong. I was obliged to
sit upon one of the steps to allow my excitement to subside; but so soon as
I had reached the Cour Verte and the woods, I began to run, to leap, to
bound, to skip, to rejoice until I fell down exhausted, panting, drunk with
frolic and liberty.
My father took me with him shooting. I was seized with the taste for sport,
and carried it to excess; I still see the field where I killed my first hare.
Often, in autumn, I have stood for four or five hours to my waist in water,
waiting at the edge of a pond for wild-duck; to this very day I lose my
composure when I see a dog point. Nevertheless, my first ardor for sport
was built upon a basis of independence; to leap ditches, to tramp over
fields, marshes, moors, to find myself with a gun in an unfrequented spot,
alone and powerful, all this was my natural manner of being. When out
shooting, I would go so far that I had not the strength to walk back, and
the keepers were obliged to carry me on twisted branches.
However, the pleasures of the chase no longer satisfied me; I was fretted
with a longing for happiness which I could neither control nor understand;
my mind and my heart ended by forming as it were two empty temples,
without altars or sacrifices; it was not yet known which god would be
worshipped there. I grew up by the side of my sister Lucile: our friendship
was all our life.
*
Lucile was tall and endowed with remarkable, but serious, beauty. Her pale
features were shaded with long black tresses; she often fixed her eyes on
heaven or cast looks around her full of sadness or fire. Her gait, her voice,
her smile, her expression showed something pensive and suffering.
Lucile and I were mutually useless. When we spoke of
the world, it was of that which we carried within
ourselves, a world very unlike the true world. She saw in
me her protector, I in her my friend. She was seized with gloomy fits of
thought which I had difficulty in dispelling: at the age of seventeen she
bewailed the loss of her youth; she wished to bury herself in a convent.
Everything to her was a care, a sorrow, a hurt: an expression she sought

for, an illusion she entertained would torment her for months on end. I
have often seen her, with one arm thrown over her head, dream without life
or movement; the life that was in her ebbed to her heart, and ceased to
show itself without; her very bosom no longer heaved. Her attitude, her
melancholy, her beauty gave her the air of a funeral Genius. I then
endeavored to console her, and the next moment was myself plunged in
inexplicable despair.
Lucile liked to read some pious book, in the evening, alone: her favourite
oratory was the junction of two country-roads, marked by a stone cross and
a poplar-tree, whose long stylus rose into the sky like a pencil. My mother,
devout and quite charmed, said that her daughter reminded her of a
Christian of the primitive Church, praying at the stations called Lauræ.
My sister's concentration of mind gave birth to extraordinary intellectual
effects: in her sleep, she dreamt prophetic dreams; waking, she seemed to
read the future. A clock ticked upon a landing of the staircase in the main
tower, and struck the hours amid the silence. Lucile, when unable to sleep,
would go to sit upon a stair opposite the clock and watch its face by the
light of her lamp placed upon the ground. When the two hands met at
midnight and in their formidable conjunction engendered the hour of
disorder and crime, Lucile heard sounds which revealed distant deaths to
her. She was in Paris a few days before the 10th of August, staying with my
other sisters near the Carmelite Convent, and casting her eyes upon a
mirror, she gave a cry, and said, "I have just seen Death come in." On the
moors of Scotland, Lucile would have been one of the celestial women of
Walter Scott, gifted with second sight; on the moors of Brittany, she was no
more than a lonely creature favoured with beauty, genius and misfortune.
*
The life which my sister and I led at Combourg heightened the exaltation
natural to our age and character. Our chief pastime was to walk side by side
in the Great Mall, in spring on a carpet of primroses, in autumn on a bed of
dead leaves, in winter on a sheet of snow edged by the footprints of birds,
squirrels, and weazels. We were young as the primroses, sad as the dead
leaves, pure as the newly-fallen snow: our recreations were in harmony
with ourselves.
It was during one of these walks that Lucile, hearing me speak rapturously
of solitude, said, "You ought to write all that down." These words revealed
the muse to me; a divine inspiration passed over me. I began to lisp verses,

Lucile's manuscript.
as though it were my natural language; day and night I sang my pleasures,
in other words my valleys and my woods; I wrote a multitude of little idylls
or pictures of nature
[162]
. I wrote in verse long before writing in prose: M.
de Fontanes used to maintain that I had received both instruments.
Did this talent which friendship foresaw for me ever really come to me?
How many things have I awaited in vain! In the Agamemnon of Æschylus, a
slave is placed as sentry on the roof of the palace of Argos; his eyes seek to
discern the concerted signal for the return of the ships; he sings to while
away his vigils, but the hours speed by and the stars set, and the torch
does not shine forth. When, after many years, its tardy light appears upon
the billows, the slave is bent beneath the weight of time; there is naught
left for him but to reap misfortunes, and the chorus says to him that "an old
man is a shadow that wanders by day."
Οναρ ἡμερόϕαντον ἀλαίνει
Under the first spell of my inspiration, I engaged Lucile to do as I did. We
spent days in mutual consultation, in communicating to each other what we
had done and what we proposed to do. We undertook works in common;
guided by our instincts, we translated the finest and saddest passages in
Job and Lucretius upon life: the Tædet animam meam vitæ meæ
[163]
, the
Homo natus de muliere
[164]
, the Tum porro puer, ut sævis projectus ab
undis navita
[165]
, and so forth. Lucile's thoughts were sheer feeling; they
issued with difficulty from her soul; but when she succeeded in expressing
them, there was nothing higher. She has left some thirty pages in
manuscript; it is impossible to read them without profound emotion. The
elegance, the suavity, the dreaminess, the passionate tenderness of these
pages present a combination of the Greek and German genius
[166]
.
*
My brother sometimes vouchsafed to spend a few
moments with the hermits of Combourg. He was in the
habit of bringing with him a young counsellor of the
Parliament of Brittany, M. de Malfilatre
[167]
, cousin to the unfortunate poet
of the same name
[168]
. I believe that, unknown to herself, Lucile felt a
secret passion for this friend of my brother's, and that this stifled passion
lay at the root of my sister's melancholy. She possessed, moreover,
Rousseau's folly without his pride: she thought that everybody was in a
conspiracy against her. She came to Paris in 1789, accompanied by her

sister Julie, whose loss she deplored with an affection tinged with the
sublime. All who knew her admired her, from M. de Malesherbes to
Chamfort
[169]
. Thrown into the revolutionary crypts at Rennes
[170]
, she was
on the point of being imprisoned at Combourg Castle, which had been
turned into a gaol during the Terror. After her release from prison, she
married M. de Caud
[171]
, who left her a widow within a year. I met the
friend of my childhood on my return from my emigration: I will tell how she
disappeared, when it pleased God to afflict me.
*
I have returned from Montboissier, and these are the last lines that I shall
trace in my hermitage; I have to leave it, filled with the tall striplings which
already hide and crown their father in their close ranks. I shall not see
again the magnolia which promised its blossom to the tomb of my fair
Floridan, the Jerusalem pine-tree and the cedar of Lebanon consecrated to
the memory of Jerome, the laurel of Granada, the Greek plane-tree, the
Armorican oak, at whose feet I drew Blanca, sang Cymodocée, invented
Velléda. These trees were born and grew with my dreams, of which they
were the hamadryads. They are about to pass under another's sway: will
their new master love them as I have loved them? He will allow them to
wither, he will cut them down perhaps: I am doomed to keep nothing upon
this earth. While bidding farewell to the woods of Aulnay I shall recall the
farewell which long ago I bade to the woods of Combourg: my days are all
farewells.
*
The taste for poetry with which Lucile had inspired me was as fuel added to
the flames. My sensations gathered new strength; vain thoughts of fame
passed through my mind; for a moment I believed in my "talent," but soon
recovered a proper mistrust of my own powers, and began to entertain
doubts of that talent, as I have always done. I looked upon my work as a
temptation of the Evil One; I was angry with Lucile for arousing an
unfortunate propensity within me: I ceased writing and began to mourn my
future glory as one might mourn his glory that is past.
Returning to my former state of idleness, I felt more strongly what was
lacking to my youth: I was a mystery to myself. I could not see a woman
without feeling confused; I blushed if she spoke to me. My shyness, already
excessive with people in general, became so great in the presence of a
woman that I would have preferred any torture to that of being left alone

Vague longings.
with her: no sooner was she gone than I recalled her with all my wishes.
The descriptions of Virgil, Tibullus and Massillon, it is true, presented
themselves to my memory; but the image of my mother and sister covered
all with its purity and made thicker the veils which nature sought to raise:
my filial and brotherly affection deceived me with respect to an affection
less disinterested. Had the loveliest slaves of the seraglio been handed over
to me, I should not have known what to ask of them. Chance enlightened
me.
A neighbor of the Combourg domain came to spend a few days at the
castle with his wife, a very pretty woman. Something, I know not what,
happened in the village; we ran to one of the windows of the hall to look. I
reached the window first, the fair visitor followed close upon my heels, I
turned to give her my place. Involuntarily she obstructed my way, and I felt
myself pressed between her and the window. I was no longer conscious of
what was happening around me.
From that moment I was aware that to love and be loved
in a manner unknown to me must be the supreme
happiness. Had I done what other men do, I should soon
have become acquainted with the pains and pleasures of the passion whose
germs I bore within me; but everything in me assumed an extraordinary
character. The ardor of my imagination, my shyness, the solitude in which I
lived caused me, rather than rush out of doors, to fall back upon myself; for
want of a real object, I evoked, by the strength of my vague longings, a
phantom which never left my side. I do not know whether the history of the
human heart offers another instance of this nature.
*
And so I built up a woman out of all the women whom I had seen: she had
the figure, the hair, the smile of the stranger who had pressed me to her
bosom; I gave her the eyes of one of the young girls of the Village, the
complexion of another. The portraits of the fine ladies of the time of
François I., Henry IV. and Louis XIV. which adorned the drawing-room
supplied me with other features, and I even borrowed graces from the
pictures of the Virgins that hung upon the church walls.
This invisible charmer accompanied me wherever I went; I communed with
her as with a real being; she varied in the measure of my folly: Aphrodite
unveiled; Diana clad in the dew and the blue of heaven; Thalia with her
laughing mask; Hebe bearing the cup of youth; sometimes she became a

fairy who laid nature at my feet. I touched and retouched my canvas; I took
one attraction from my beauty to replace it with another. I also changed her
finery; I borrowed it from every country, every century, every art, every
religion. Then, when I had completed a masterpiece, I dispersed my
drawings and paints again; my one woman turned into a crowd of women
in whom I idolized separately the charms I had adored when united.
Pygmalion was less enamored of his statue: my difficulty was how to please
mine. Recognizing in myself none of the qualities calculated to awaken love,
I lavished upon myself all that I lacked. I rode like Castor and Pollux; I
played the lyre like Apollo; Mars wielded his arms with less power and skill:
a hero of romance or history, I heaped fictitious adventures on fiction itself!
The shades of Morven's daughters, the sultanas of Bagdad and Granada,
the ladies of the castles of olden time; baths, perfumes, dances, Asiatic
delights were all borne to me by a magic wand.
See this young queen coming, decked in diamonds and flowers (it was still
my sylph): she fetches me at midnight, across gardens of orange-trees, in
the galleries of a palace bathed by the waves of the sea, on the balmy
shore of Naples or Messina, beneath a sky of love pierced by the light of
Endymion's star; she advances, an animated statue by Praxiteles, amidst
motionless statues, pale pictures and frescoes white and silent in the
moonlight: the soft sound of her progress over the marble mosaic mingles
with the imperceptible murmurs of the deep. The royal jealousy
encompasses us. I fall at the knees of the sovereign of Enna's plains; the
silk waves from her loosened diadem fall caressingly upon my brow as she
bends her girlish head over my face, and her hands rest upon my breast,
throbbing with respect and with desire.
On emerging from these dreams, when I found myself once more a poor
little obscure Breton lad, without fame, beauty, or talents, who would
attract the looks of none, who would pass unknown, whom no woman
would ever love, I was seized with despair: I no longer dared lift my eyes to
the dazzling image I had attached to my steps.
This delirium lasted two whole years, during which the faculties of my soul
attained the loftiest pitch of exaltation. I used to speak little, I now spoke
not at all; I used still to study, I flung my books aside; my taste for solitude
redoubled. I had all the symptoms of a violent passion: my eyes grew
hollow; I fell away; I could not sleep; I was absent, melancholy, ardent,

The Sylph of my
dreams.
fierce. My days slipped by in a manner that was wild, odd, insensate, and
yet full of delights.
To the north of the castle stretched a waste land strewn with druidical
stones; I would go and sit upon one of these stones at sunset. The gilded
summit of the woods, the splendor of the earth, the evening star twinkling
through the rosy clouds brought me back to my dreams: I longed to enjoy
this sight with the ideal object of my desires. I followed in thought the
luminary of the day; I gave him my beauty to escort, so that he might
present her all radiant with himself to the homage of the universe. The
evening breeze shattering the web woven by insects upon the tips of the
blades of grass, the field-lark alighting upon a pebble recalled me to reality:
I turned my steps back to the castle, with heart oppressed and downcast
face.
On stormy days in summer, I climbed to the top of the
great west tower. The thunder roaring beneath the castle
lofts, the torrents of rain which fell dashing upon the
cone-shaped roof of the towers, the lightning which furrowed the clouds
and marked the brass weathercocks with its electric flame aroused my
enthusiasm: like Ismen on the ramparts of Jerusalem, I invoked the
thunder, I hoped that it would bring Armida to me.
If the sky was clear, I crossed the Great Mall, around which lay meadows
divided by hedges of willow-trees. In one of these willows, I had contrived
a seat, like a nest: here, isolated between heaven and earth, I spent hours
with the singing birds; my nymph was by my side. I also associated her
image with the beauty of those spring nights filled with the freshness of the
dew, the sighs of the nightingale and the murmuring of the breeze.
At other times I followed a deserted path, a stream adorned with its river-
side plants; I listened to the sounds that issued from unfrequented parts; I
lent an ear to every tree; I thought I heard the moonlight singing in the
woods: I tried to tell these pleasures, and the words died upon my lips. I
know not how I found my goddess again in the accents of a voice, the
vibration of a harp, the velvety or liquid sounds of a horn or an harmonica.
It would take too long to describe the fine journeys I took with my flower of
love; how, hand in hand, we visited famous ruins, Venice, Rome, Athens,
Jerusalem, Memphis, Carthage; how we crossed the seas; how we asked
happiness of the palm-trees of Otaheite, of the scented groves of Timor
and Amboyna; how, on the summit of the Himalayas, we went to wake the

dawn; how we descended the sacred rivers whose spreading waves encircle
gilt-domed pagodas; how we slept on the banks of the Ganges, while the
Bengali, perched on the mast of a bamboo wherry, sang his Hindoo boat-
song. Earth and Heaven no longer existed for me; above all, I forgot the
latter; but though it no longer received my prayers, it heard the voice of my
secret misery: for I suffered, and sufferings pray.
*
The sadder the season, the greater its harmony with myself; the time of
hoar-frost makes communication less easy and isolates those who dwell in
country-places: one feels more beyond the reach of men.
A moral character clings to autumn scenery: those leaves which fall like our
years, those flowers which fade like our days, those clouds which fleet like
our illusions, that light which fails like our intelligence, that sun which cools
like our love, those streams which freeze like our life bear a secret relation
to our destinies.
I beheld with ineffable pleasure the return of the season of storms, the
passing of the swans and the ring-doves, the muster of the crows on the
pond field, and their perching at nightfall on the tallest oaks in the Great
Mall. When the evening raised a bluish vapor in the cross-roads of the
forest, and the plaintive lays of the wind moaned in the withered moss, I
entered into full possession of the sympathies of my nature. If I met some
ploughman at the end of a field, I stopped to look at that man who had
shot up in the shadow of the wheat with which he was to be reaped, and
who, turning over the earth of his tomb with the plough-share, mingled his
burning sweat with the icy rains of autumn: the furrow which he dug was
the monument intended to outlive him. What did my elegant dæmon then
do? By means of her magic, she wafted me to the banks of the Nile, and
showed me the Egyptian pyramid sunk beneath the dust, as one day the
Armorican furrow would lie hidden beneath the heather: I congratulated
myself on having placed the fables of my felicity beyond the circle of human
realities.
In the evening I embarked upon the pond, and, alone in my boat, rowed
amidst the rushes and the broad floating leaves of the water-lilies.
Overhead was the meeting-place of the swallows preparing to quit our
climes. Not one of their twitterings did I lose; the child Tavernier
[172]
followed less closely the traveller's tale. They played on the water at
sundown, chased the flies, darted together into the air, as though to test

Nocturnal
incantations.
their wings, dropped down upon the surface of the lake, and then perched
upon the reeds, which scarcely bent beneath their weight, and which were
filled with their warbling turmoil.
Night fell; the reeds shook their fields of swords and distaves, among which
the feathered caravan of moor-fowl, teal, kingfishers, snipe lay silent; the
lake washed against its shores; the loud voices of autumn issued from the
woods and marshes; I ran my boat aground and returned to the castle. Ten
o'clock struck. I went to my room, and at once opened the windows, fixed
my eyes upon the sky, and commenced an incantation. In company with my
witch I mounted the clouds: enveloped in her tresses and her veil, I was
swept along by the tempest, shaking the forest-tops, hustling the
mountain-summits, whirling upon the seas. I plunged into space, I dropped
from the Throne of God to the gates of the abyss, and the worlds were
surrendered to the power of my love. Amid the disorder of the elements, I
frenzically wedded the idea of danger to that of pleasure. The breath of the
north wind brought to me but the sighs of voluptuousness; the murmur of
the rain summoned me to sleep upon a woman's breast. The words which I
addressed to that woman would have revived the senses of old age and
warmed the marble of the tombs. Nothing-knowing and all-knowing, at
once maid and lover, Eve before and after the fall, the enchantress from
whom I derived my madness was a commixture of mystery and passion: I
placed her on an altar and worshipped her. The pride of being loved by her
yet further increased my love. When she walked, I prostrated myself to be
trod beneath her feet or kiss their traces. I grew confused at her smile; I
trembled at the sound of her voice; I thrilled with desire if I touched what
she had touched. The air exhaled from her moist mouth penetrated into the
marrow of my bones, coursed through my veins instead of blood. At a look
from her I would have flown to the ends of the earth: a desert would have
sufficed me with her! With her at my side, the lions' den would have
changed into a palace, and millions of centuries would have been too short
to exhaust the fires with which I felt myself consumed.
To this madness was added a moral idolatry: by a further
play of my imagination, the Phryne that clasped me in
her arms also represented glory to me and, above all,
honour; virtue performing its noblest sacrifices, genius conceiving the rarest
thoughts would scarcely give an idea of this other kind of happiness. I
found at one and the same time in my marvelous creation all the
blandishments of the senses and all the joys of the soul. Overwhelmed and

as it were submerged beneath these dual delights, I no longer knew which
was my true existence: I was a man and was not a man; I became cloud,
wind, sound; I was a pure spirit, a creature of the air, singing the sovereign
felicity. I divested myself of my nature to become one with the maiden of
my desires, to be transmuted into her, to touch beauty more closely, to be
at once passion given and received, love and the object of love. Suddenly,
struck with my madness, I flung myself upon my couch; I rolled myself in
my grief; I watered my pillow with scalding tears which none saw, piteous
tears which flowed for a nonexistent thing.
*
Soon, no longer able to remain in my tower, I climbed down through the
darkness, furtively opened the door leading to the steps, like a murderer,
and went to wander in the great wood. After walking at random, waving my
hands, embracing the winds which escaped me like the shadow, the object
of my pursuit, I leant against the trunk of a beech-tree; I watched the
crows which I made fly from one tree to settle on another, or the moon
lingering over the unclothed summits of the forest: I would have liked to
inhabit this dead world, which reflected the pallor of the tomb. I felt neither
the cold nor the dampness of the night; not even the icy breath of dawn
would have drawn me from the depth of my thoughts, if at that hour the
village bell had not made itself heard.
In most of the villages of Brittany, it is the custom at daybreak to toll the
bell for the dead. The peal consists of three repeated notes, which give a
monotonous, melancholy, rustic little tune. Nothing suited my sick and
wounded soul better than to be recalled to the tribulations of existence by
the bell which announced its end. I pictured to myself the herdsman
expiring in his unknown hut, and laid in a graveyard no less unknown. What
had he come to do in the world? And I, what was I doing in this world?
Since I should have to go at last, was it not better to depart in the cool of
morning, to arrive early, than to complete the journey beneath the weight
and in the heat of day? The blush of longing mantled on my face; the idea
of ceasing to exist took possession of my heart in the manner of a sudden
joy. At the period of the errors of my youth, I often hoped not to outlive
happiness: there lay in the first success a measure of felicity that led me to
aspire to destruction.
Bound ever more closely to my phantom, unable to enjoy what did not
exist, I was like those mutilated men who contemplate a state of bliss to

I attempt my life.
them unattainable and conjure up dreams whose pleasures rival the
tortures of hell. I had, moreover, a presentiment of the misery of my future
lot; ingenious in the fabrication of sufferings, I had placed myself between
two forms of despair: sometimes I thought myself a mere nullity, incapable
of rising above the vulgar herd; sometimes I seemed to feel within myself
qualities which would never be appreciated. A secret instinct warned me
that, as I moved onward through the world, I should find no part of that
which I sought.
Everything furnished food for the bitterness of my disgust: Lucile was
unhappy; my mother did not console me; my father made me feel the
terrors of life. His moroseness increased with years; old age stiffened his
soul as it did his body; he constantly spied upon me to chide me. When I
returned from my wild rounds and saw him sitting on the steps, one might
have killed me rather than make me enter the castle. Yet this but
postponed my torture: obliged as I was to appear at supper, I sat down
sheepishly upon the edge of my chair, my cheeks wet with the rain, my hair
entangled. I sat motionless beneath my father's glances, and the
perspiration stood upon my brow: the last glimmer of reason escaped me.
I now come to a moment when I shall need some
strength to confess my weakness. The man who
attempts to take his own life displays less the vigor of his
soul than the exhaustion of his nature. I owned a fowling-piece whose worn
trigger often went off when uncocked. I loaded this gun with three bullets,
and went to a remote part of the Great Mall. I cocked the gun, placed the
muzzle of the barrel in my mouth, and struck the butt-end against the
ground; I several times repeated the ordeal; the charge did not go off; the
appearance of a keeper stopped my resolve. Involuntary and unconscious
fatalist that I was, I presumed that my hour had not come, and I deferred
the execution of my project to another day. Had I killed myself, all that I
have been would have been buried with me; none would have known of
the history that led to my catastrophe; I should have swelled the crowd of
nameless unfortunates, I should not have let myself be followed by the
traces of my sorrows as a wounded man is followed by the traces of his
blood.
Those who might be troubled by these descriptions and tempted to imitate
these follies, those who might attach themselves to my memory through
my illusions, must remember that they are listening only to a dead man's

My new career.
voice. Reader, whom I shall never know, nothing remains: nought is left of
me save that I am in the hands of the living God who has judged me.
An illness, the fruits of this unruly life, put an end to the torments which
brought me the first inspirations of the Muse and the first attacks of the
passions. These passions with which my soul was overwrought, these yet
vague passions resembled the storms at sea which rush from every point of
the horizon: inexperienced pilot that I was, I knew not in which direction to
spread my sail to the uncertain winds. My chest swelled, a fever laid hold of
me; they sent to Bazouges, a small town some five or six leagues from
Combourg, for an excellent doctor called Cheftel, whose son
[173]
played a
part in the affair of the Marquis de La Rouërie. He examined me attentively,
ordered remedies, and declared that it was essential that I should be
removed from my present mode of life. I lay six weeks in danger. One
morning my mother came and sat on my bed, and said:
"It is time for you to take a decision; your brother is in a position to obtain
a benefice for you; but before going to the seminary, you must take good
counsel with yourself, for although I wish you to adopt the ecclesiastical
state, I would rather see you a man of the world than a scandalous priest."
Those who have read the foregoing pages will be able to judge if the
proposal of my pious mother came at a good moment. I have always, in the
more important events of my life, at once known what to avoid: I am
prompted by a movement of honor. As a priest, I struck myself as
ridiculous. As a bishop, the majesty of the sacerdotal office overawed me,
and I respectfully recoiled before the altar. Should I, as a bishop, make
efforts to acquire virtues, or content myself with hiding my vices? I felt
myself too weak to take the first course, too candid to adopt the second.
They who treat me as a hypocrite and an ambitious man know me but
little; I shall never succeed in the world, precisely because I lack one
passion and one vice: ambition and hypocrisy. The first of these would with
me be at the most a form of injured self-love; I might sometimes wish to be
a minister or king in order to laugh at my enemies; but in twenty-four hours
I should throw my portfolio or my crown out of window.
I therefore told my mother that my religious vocation
was not sufficiently strong. For the second time I
changed my plans: I had refused to become a sailor, and
now I was no longer willing to be a priest. There remained the military
career, which I loved: but how to suffer the loss of my independence and

the restraint of European discipline? I took an absurd idea into my head: I
declared that I would go to Canada and clear forests, or to India and take
service in the armies of the princes of that country. By one of those
contrasts which we perceive in all men, my father, so reasonable in other
respects, was never greatly shocked by an adventurous project. He chided
my mother for my fickleness, but decided to ship me to India. I was
dispatched to Saint-Malo, where an expedition was being fitted out for
Pondicherry.
*
Two months elapsed: I found myself back and alone in my maternal island.
Villeneuve had just died there. I went to weep for her beside the poor,
empty bed on which she had breathed her last, and saw the little wicker
go-cart in which I had learnt to stand upright upon this world of sorrows. I
pictured my old nurse lying on her pillow and fixing her feeble gaze upon
that basket on wheels: this first memorial of my life opposite the last
memorial of the life of my second mother, the thought of the wishes for the
happiness of her nursling which the kind Villeneuve addressed to Heaven
on leaving this world, this proof of an attachment so constant, disinterested
and pure broke my heart with tenderness, gratitude and regret.
I found nothing else to remind me of my past at Saint-Malo: in the harbor I
sought in vain for the ships in whose rigging I had played; they were gone
or broken up; in the town, the house where I was born had been turned
into an inn. I was scarce out of my cradle, and already a whole world had
fallen into decay. I was a stranger in the parts of my childhood; people who
met me asked who I was, for the sole reason that my head rose a few
inches higher above the ground towards which it will sink again in a few
years. How rapidly and how often we change our manner of existence and
our illusions! Friends leave us, others take their place; our ties alter: there
is always a time at which we possessed nothing of what we now possess,
at which we have nothing of what we once had. Man has not one self-same
life: he has several on end, and that is his calamity.
*
Henceforward friendless and alone, I explored the beach which had borne
my sand-castles: campos ubi Troja fuit. I walked on the shore deserted by
the sea. The strand abandoned by the rising tide offered me the picture of
those desolate places which our illusions leave around us when they go.
Abailard, my fellow-Breton
[174]
, like myself watched these rollers eight

hundred years ago, thinking of his Héloïse; like me, he saw some vessel
speed (ad horizontis undas), and his ear, like mine, was lulled with the
monotone of the waves. I exposed myself to the breakers while indulging in
the baleful imaginings which I had brought with me from the woods at
Combourg. A head called Cap Lavarde was the limit of my walks: seated at
the extremity of this head, I remembered with the bitterest reflections that
these same rocks had served to hide me as a child during the fairs; I had
there gulped down my tears, while my playmates elated themselves with
joy. I felt neither better loved nor happier than at that time. Soon I was to
leave the country of my birth to crumble away my days in various climes.
These reflections wounded me to death, and I was tempted to let myself
fall into the waves.
A letter called me back to Combourg: I arrived, I supped with my family,
monsieur my father did not speak a word, my mother sighed, Lucile
appeared dismayed. At ten o'clock we retired. I questioned my sister; she
knew nothing. At eight o'clock the next morning I was sent for. I went
downstairs: my father was waiting for me in his study.
"Monsieur le chevalier," he said, "you must renounce your follies. Your
brother has procured you a sub-lieutenant's commission in the Navarre
Regiment. You will go first to Rennes, and thence to Cambrai. Here are a
hundred louis: be sparing with them. I am old and ill; I have not long to
live. Conduct yourself as a good man and never disgrace your name."
He kissed me. I felt that severe, wrinkled face press with emotion against
mine: it was the last paternal embrace I was to receive.
At that moment the Comte de Chateaubriand, a man so formidable in my
eyes, appeared to me only as a father most worthy of my affection. I flung
myself upon his emaciated hand and wept. He was threatened with an
approaching attack of paralysis, which brought him to the grave; his left
arm had a convulsive movement which he was obliged to check with his
right hand. He was thus holding his arm when, after giving me his old
sword, without leaving me time to recover myself, he led me to the
cabriolet which was waiting for me in the Cour Verte. He made me get in
before him. The post-boy drove off, while I with my eyes bade farewell to
my mother and sister, who dissolved into tears on the steps.
I drove along the road by the pond; I saw the reeds of my swallows, the
mill-stream and the meadow; I cast a look at the castle. Then, like Adam

Last visits to
Combourg.
after his sin, I proceeded towards unknown ground, and "the world was all
before me
[175]
."
*
From that day I saw Combourg but three times: after my
father's death we met, in mourning, to share our
inheritance and take leave of each other. On another
occasion I accompanied my mother to Combourg: she was engaged in
furnishing the castle, in expectation of the arrival of my brother, who was to
bring my sister-in-law to Brittany. My brother did not come; he was soon,
with his young wife, to receive at the hands of the executioner a different
pillow from that prepared by my mother's hands. Lastly, I passed through
Combourg a third time on my road to Saint-Malo to embark for America.
The castle was abandoned, I had to put up at the steward's lodge.
Wandering through the Great Mall, from the bottom of a dark avenue I
caught sight of the deserted steps, the closed door and windows, and
fainted away. I had difficulty in making my way back to the village: I sent
for my horses and left in the middle of the night.
After an absence of fifteen years, and before again leaving France on my
visit to the Holy Land, I went to Fougères to embrace what remained of my
family. I had not the courage to undertake the pilgrimage to the fields to
which the most vivid portion of my existence was attached. It is in the
woods of Combourg that I became what I am, that I began to feel the first
attacks of the weariness which I have dragged with me through life, of the
sadness which has been my torment and my felicity. There I sought for a
heart that could beat in touch with mine; there I saw my family united only
to disperse. My father there dreamt of his name restored, of the fortunes of
his house revived: another illusion which time and the revolutions have
dispelled. Of six children that we were, we remain but three: my brother,
Julie and Lucile are no more, my mother died of grief, my father's ashes
were snatched from his grave.
If my works survive me, if I am to leave a name behind me, perhaps one
day, prompted by these Memoirs, some traveller will come to visit the spots
I have depicted. He will be able to recognize the castle; but he will look in
vain for the great wood: the cradle of my dreams has vanished like those
dreams. Left standing alone upon its rock, the ancient keep mourns the
oaks, the old friends that surrounded it and protected it against the storm.
Isolated also, I too have seen falling around me the family which beautified

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Biophotonics Concepts To Applications 2nd Gerd Keiser

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