Liquid Crystals.pdf brief of nanocomposites

Nanocomposites

1. LECTURE - 5
Liquid crystals: Classification, Properties
and Applications

2. Liquid Crystals are state of matter which has properties between those of
conventional liquids and solid crystals. For example, a liquid crystal may flow
like a liquid, but its molecules may be oriented in a crystal-like way.
The liquid-crystalline state is often called mesomorphic state (mezos
meaning "intermediate"), and the liquid crystals are called mesophase.
LIQUID CRYSTALS
Friedrich Reinitzer, Austrian botanist studied about it first in
1888 in a material known as cholesteryl benzoate .

4. Following character describe the crystalline
structure:

Positional order: the extent to which an average molecule or
group of molecules shows translational symmetry (as
crystalline material shows).

Orientational order: represents a measure of the tendency of
the molecules to align along the directon on a long-range
basis.

5. Bond Orientational Order: describes a line joining the centres of
nearest neighbour molecules without requiring a regular spacing
along that line.

Positional order + Orientational order = crystal phase

Varying Positional order + Orientational order = LC phase

6. Positional order + Orientational order = Crystal Phase
Positional order + No Orientational order = Plastic Phase
Varying Positional order + Orientational order = Liquid crystalline
Phase
No positional order + No Orientational order = Isotropic (Liquid)
Phase

8. Properties of liquid crystals

The molecules are rod shaped or disc shaped.
All liquid crystals are mesogens but all mesogens are not liquid crystals.
Molecules are anisotropic in nature.
Assuming that the direction of preferred orientation in a liquid crystal
(LC) is ↑, this direction can be represented by an arrow, called the
director of the LC.

9. Each molecule is orientated at some angle to the director.
These molecules possess very strong dipole moment.
The liquid crystal molecules prefer to align parallel to each
other because of the strong intermolecular attraction (π-π
interaction).
A typical Liquid Crystal molecule is represented by a central
rigid part, known as mesogen (generally aromatic) and the
flexible ends (generally aliphatic groups).

10. long range order and short range order
•Crystalline solids have a long range order which means that there is a
regular pattern of arrangement of particles which repeats itself
periodically over the entire crystal. Whereas, amorphous solids consist of
particles of irregular shape and have short range order only.

Aanisotropy
Anisotropy is the property of being directionally dependent, as opposed to
isotropy (homogeneity in all directions). It can be defined as a difference in
the physical property of a certain material when measured along different
axes.
For example many materials exhibit very different properties when
measured along different axes: physical or mechanical
properties (absorbance, refractive index, conductivity, tensile strength, etc.)

11. It consists of two or more ring systems
connected by a central linkage group.

12. Essential requirements for a molecule to be a
liquid crystal
Shape of the molecule must be rod like or disc like.
Molecule must be anisotropic in nature.
Molecule must have some rigidity in its central region
and the ends must be flexible.
Although LC’s combine the properties of a crystalline solid
and an isotropic liquid, they exhibit very specific electro-
optical phenomena, which have no equivalent analogues in
solids or in liquids.

13. Classification of liquid crystals:
Liquid Crystals
Lyotropic L.C.
(Solvent dependent)
Thermotropic L.C.
(Temperature dependent)
Calamatic L.C.
(Rod shaped)
Discotic L.C.
(Disc Shaped)
Smectic
L.C.
Nematic L.C.
Smectic A
Smectic C
Ordinary Nematic
Nematic Cholesteric
Discotic Nematic Discotic Columnar
Lamellar Cubic Hexagonal

14. 1. Thermotropic liquid crystals:

They are formed by change of temperature. They
occur as liquid crystals over a certain temperature
range between the solid and liquid phase. Example
– LCD TV’s, alarm clocks.

15. Compound Transition
temperature
(°C)
Melting
Temperature (°C)
p-azoxy anisole 116 135
p-methoxy
cinnamic acid
170 186
Dibenzal benzidine 235 260
Examples of Thermotropic LCs:
Types of Thermotropic LCs:- Nematic, Sematic, Chiral.

16. Thermotropic liquid crystals are further classified into:
a) Calamatic L.C.(Rod like or elongated molecules)
b) Discotic Liquid Crystals (Disc shape molecules)
Calamatic liquid crystals are elongated, rod shaped
molecules. They are further classified as Nematic and
Smectic liquid crystals.

17. Nematic liquid crystals


•Word Nematic derived from Greek word
Nema which means "thread".
•No positional order, but possess
orientational order.
•Molecule have elongated rod like shape
and are thread like.
•Do not have layered structure.
•Flow like normal liquids.
•They have low viscosity.
•Formed at relatively higher temperature.

18.  Can be aligned by the
application of electric on
magnetic field.
 Molecules are free to move in
all the directions.
 Flow in all directions & not in
layers.
 E.g.- p-azoxy anisole (first
synthetic liquid crystal to be
produced).

19. Nematic liquid crystals can be further
classified as:
a) Ordinary nematic phases: These
molecules possess ordinary nematic phase
characteristics as discussed earlier.
b) Cholesteric nematic phases: This phase
is also known as chiral nematic phase. The
molecules are essentially chiral and resembles
nematic molecules in nature.

20. Cholesteric Liquid Crystals
(Chiral Nematic)
•This phase is usually observed from cholesterol
derivatives.
•The molecules are essentially chiral.
•The molecules are arranged in layers.
•These are formed by adding chiral twisting agent to
the nematic liquid crystals.

22. Each layer in Cholesteric liquid crystal is tilted with respect to
the other one, and hence the molecules take a one complete
turn of 360 degrees to make a helix.
 The distance covered by the director in making a one
complete turn is known as pitch.

23. Cholesteric Liquid crystal
reflects light
approximately equal to
pitch.
 Pitch is inversely
proportional to the
temperature.
Pitch is affected by
temperature, pressure as
well as by electric and
magnetic fields.

24. Smectic Liquid Crystals:

•Molecules are soap shaped.
•Have short range orientational as well as positional order.
•These are arranged in layers i.e. have layered structure.
•They do not flow like normal liquids and has limited
mobility.
•They have high viscosity.
•Not affected by external electric or magnetic field.

25. Molecules are free to move
within the layers, but not
from one layer to another.
Flow in layers and difference
layers can slide over one
another.
 Are of two types: Smectic A
and C.
E.g.: Ethyl-para-azoxy
phenetole.

26. Discotic Liquid Crystals:

Molecules are essentially disc shaped.
Discotic mesogens are typically composed of an
aromatic core surrounded by flexible alkyl
chains. The aromatic cores allow charge transfer in
the stacking direction through the π conjugate
systems. The charge transfer allows the discotic liquid
crystals to be electrically semi conductive along the
stacking direction.
They are of two types: Discotic nematic Phase and
Columnar Phase.

27. Disc-shaped molecules have a tendency to lie on top of one
another forming either discotic nematic phases (with discs
oriented similar to that of nematic phase i.e. not having position
order but having orientation order) or columnar phases (have
column-like structure).

28. Liquid Crystal Phases

29. Lyotropic Liquid Crystals:

•Lyotropic liquid crystals are two component systems, where
an amphiphile is dissolved in a solvent.
•Thus, lyotropic mesophases are solvent and concentration
dependent.
•The amphiphillic compounds are characterized by two
different moieties, a hydrophilic polar head and a
hydrophobic tail.

30. •LLC are made by adding solvent to the solid until critical micelle
concentration (CMC) is reached. On further addition of solvent
LLC changes into liquid phase.
•Examples: molecules of soaps, phospholipids (present in cell
membranes), toothpaste, many proteins and cell membranes,
tobacco mosaic virus.

32. Three types of lyotropic liquid crystals are well known. These are:
lamellar, hexagonal and cubic phases.
i) The simplest liquid crystalline phase that is formed by spherical
micelles is the ‘micellar cubic’, denoted by the symbol I
1. This is a
highly viscous, optically isotropic phase in which the micelles are
arranged on a cubic lattice.
ii) At higher amphiphile concentrations the micelles fuse to form
cylindrical aggregates of indefinite length, and these cylinders are
arranged on a long-ranged hexagonal lattice. This lyotropic liquid
crystalline phase is known as the ‘hexagonal phase’, and is
generally denoted by the symbol HI.

33. iii) At higher concentrations of amphiphile the ‘Lamellar
Phase' is formed. This phase is denoted by the symbol
L
α. This phase consists of amphiphilic molecules are
arranged in bilayer sheets separated by layers of water.

35. Liquid crystal polymers (LCPs) consist of
repeated monomer units but which are
linked to form extended chain-like
molecules. The primary units of the
polymeric chain are attached to one
another via a flexible linker which can be
of varying lengths (Fig). These polymeric
chains aggregate to form LCPs just as
single mesogen molecules do to form
liquid crystals. The extended chain length
of the polymeric units, however, affects
enhanced intermolecular interactions
between the polymeric chains and thus
has profound effects upon LCP behavior
distinct from simple (nonpolymeric) liquid
crystals.
Liquid Crystal Polymers (LCPs)

36. Liquid Crystal Polymers (LCPs)


Polymer liquid crystals (PLCs) are a class of materials that
combine the properties of polymers with those of liquid
crystals.
These “hybrids” show the same mesophases characteristic
of ordinary liquid crystals, yet retain many of the useful and
versatile properties of polymers.
Types of liquid crystal polymers;
1.Main chain liquid crystal polymers (MCLCPs)

2.Side chain liquid crystal polymers (SCLCPs)

37. •Main-chain polymer liquid crystals or MC-PLCs are formed when the mesogens
are themselves part of the main chain of a polymer.
•Side chain polymer liquid crystals or SC-PLCs are formed when the mesogens
are connected as side chains to the polymer by a flexible "bridge" (called the
spacer.)

38. Applications of liquid crystals:

•Liquid crystals are used for decorative purpose in cosmetics.
•LC’s based delivery system such as cream, ointment,
transdermal patches etc have been used in pharmaceutical.
•Thermotropic Cholesteric liquid crystals are used in body care
cosmetics.
•Due to their colour effect Cholesteric liquid crystals are used in
nail paints, eye shadows etc.
•Discotic liquid crystals are used in photovoltaic
devices, organic light emitting diodes (OLED), and molecular
wires.

39.  Liquid crystals are used for displays in LCD's,
Calculator, wrist watches etc.
 Have Medical applications like localized drug delivery.
 To detect radiations& pollutants in atmosphere.
 Used in non-destructive testing.
Cholesteric liquid crystals are used in coloured
thermometers.
 Used to locate tumours, veins, arteries, infections,
foetal placenta etc.

41. Liquid crystals are a unique state of matter that exhibit properties of both liquids and solids. They have a
distinct molecular arrangement that allows them to flow like a liquid while maintaining some degree of
order like a solid. This unique behavior makes them useful in various applications. Here are some
common applications of liquid crystals:
•Liquid Crystal Displays (LCDs): LCDs are widely used in electronic devices such as televisions,
computer monitors, smartphones, and digital watches. In LCDs, liquid crystals are sandwiched
between two glass plates and controlled by an electric field. By manipulating the alignment of liquid
crystal molecules, LCDs can selectively block or allow light to pass through, creating images or text.
•Optical Devices: Liquid crystals are used in various optical devices, including polarizers, optical
shutters, and variable optical attenuators. By applying an electric field, the orientation of liquid
crystal molecules can be controlled, allowing the manipulation of light polarization, transmission, and
intensity.
•Thermometers: Liquid crystals can be used in thermometers to indicate temperature changes. The
liquid crystal material changes color at specific temperature ranges, providing a visual indication of
the temperature.
•Smart Windows: Liquid crystals can be incorporated into windows to control the amount of light and
heat passing through. By applying an electric field, the transparency of the liquid crystal layer can be
adjusted, allowing for the regulation of light and heat transmission.
Liquid Crystal and Its Applications

42. Liquid Crystal and Its Applications

•Biomedical Applications: Liquid crystals have been used in various biomedical applications,
including drug delivery systems, biosensors, and tissue engineering. They can be used to
encapsulate and release drugs at specific locations, detect biological molecules, and provide
scaffolds for tissue growth.
•Electro-Optical Devices: Liquid crystals are used in electro-optical devices such as
modulators, switches, and beam deflectors. By applying an electric field, the refractive index
of liquid crystals can be changed, allowing for the manipulation of light propagation and
beam steering.

•These are just a few examples of the wide range of applications of liquid crystals. Their
unique properties make them versatile materials in various fields, including electronics,
optics, thermodynamics, and biomedicine.

45. LCD is a flat-panel display or other electronically modulated optical device that uses the light-modulating
properties of liquid crystals combined with polarizers.

Liquid crystals do not emit light directly but instead use a backlight or reflector to produce images in color
or monochrome. LCDs are available to display arbitrary images or fixed images with low information content, which
can be displayed or hidden.

They use the same basic technology, except that arbitrary images are made from a matrix of small pixels, while
other displays have larger elements. LCDs can either be normally on (positive) or off (negative), depending on the
polarizer arrangement.

For example, a character positive LCD with a backlight will have black lettering on a background that is the color of
the backlight, and a character negative LCD will have a black background with the letters being of the same color
as the backlight. Optical filters are added to white on blue LCDs to give them their characteristic appearance.
LCDs are used in a wide range of applications, including LCD televisions, computer monitors, instrument
panels, aircraft cockpit displays, and indoor and outdoor signage.

Small LCD screens are common in LCD projectors and portable consumer devices such as digital
cameras, watches, calculators, and mobile telephones, including smartphones. LCD screens have replaced heavy,
bulky and less energy-efficient cathode-ray tube (CRT) displays in nearly all applications.
Liquid-crystal display (LCD)

46. Liquid-crystal display (LCD)

47. How do nematic liquid crystals work?
A nematic liquid crystal is a transparent or translucent liquid that causes the polarization (that is, the
focusing in a plane) of light waves to change as the waves pass through the liquid. The extent of the change
in polarization depends on the intensity of an applied electric field. Nematic liquid crystals are used
in twisted nematic display s, the most common form of liquid crystal display.

A typical nematic liquid crystal produces a 90-degree shift in the polarization of the light passing through
when there is no electric field present. When a voltage is applied, an electric field is produced in the liquid,
causes change in the orientation of the molecules. This causes the polarization shift to be reduced. The effect is
slight at low voltages, and increases as the voltage (and the resulting field strength) increases. When the
applied voltage reaches a certain level, the polarization shift disappears entirely.

Because their light transmission properties can be deliberately varied as a function of applied external voltage,
nematic liquids are used in alphanumeric liquid-crystal displays ( LCD s), such as those found in digital
wristwatches and many consumer electronic devices

48. Advantages of LCD:

Low power consumption: Power consumption is typically of the order of micro watts for the display in
comparison to the some order of milliwatts for LEDs.

Sharpness: Image is perfectly sharp at the native resolution of the panel. LCDs using an analog input require
careful adjustment of pixel tracking/phase (see Interference, below).

Geometric Distortion: Zero geometric distortion at the native resolution of the panel. Minor distortion for
other resolutions because the images must be re-scaled.

Brightness: High peak intensity produces very bright images. Best for brightly lit environments.
Physical Thin, with a small footprint. Consume little electricity and produce little heat.

49. Liquid Crystal Display (LCD)

53. OFF state

54. ON state

56. What Is Optical Switch?
•As the name implies, the optical switch uses light induction to trigger the switches. The most direct
understanding of optical switch is a device used to open or close an optical circuit. It consists of mechanical,
optomechanical, or electronic types.
• It works with the mechanical switch to block the light beam. When the switch is pressed, the stem of the
switch moves downward, triggering the light sensor on the PCB and activating the key.
•That’s why optical switches are faster than the traditional switch as no physical contact is needed to send an
electrical signal; eliminating the need for a debounce delay. Also, because there is no physical contact, these
switches are usually more durable.
•The lifespan of the traditional switch is 50 million key presses while the optical switch can double that life
span and can last 100 million.
Applications of LCs in optical switches

57. Optical Switches
•An optical switch serves the same function of the electrical counterpart: it is a device with one input
and multiple outputs, and by selecting the position of the switch, it is possible to transmit all the light
to the selected channel. The switch is a programmable device, with the user that can select one
permanent output, switch between multiple channel at a preset time, or rapid switching all the
channels to interrogate multiple sensors.

•An optical switch is a multi-port network bridge, which connects multiple optic fibers to each
other and controls data packets routing between inputs and outputs.

•They can reduce the cost of the network and increase fiber transmission capacity and at the
same time, distribute optical signals to different subscribers.

•The most direct understanding of optical switch is a device used to open or close an optical circuit.

•Mechanical switch is triggered by a metal leaf Optical switch is triggered by the light signal

58. Applications of LCs in optical switches
•The high optical anisotropy of liquid crystals implies large phase shifts in very short
optical paths. Furthermore, their strong electro-optical effect allows for the rapid
reorientation of their optical axis with, indeed, very low voltage in the range of only a
few volts, hence, making liquid crystals compatible for optical switches.

•In the past few years, LC cells appear as one of the promising technologies to achieve
optical switching in telecommunications networks as these devices do not need moving
parts to switch, but a control voltage. Also, optical switching employs liquid crystal (LC)
materials due to their extreme sensitivity to applied fields, low power consumption, long
lifetime and to their low cost.

•Optical switches are based on twisted nematic (TN) LCs and surface-stabilized
ferroelectric liquid crystals (SSFLC). More recently, systems based on polymer-
dispersed liquid crystal (PDLC) have also been developed.

59. Advantages of LCs in optical switches
Optical switches have a faster and more sensitive trigger response: Since optical
switches are triggered by the acceptance of optical, as long as the displacement blocks
the optical, it can produce a signal.

Optical switches have a longer life span: When mechanical switches experience
problems, it generally is related to problems with the foot pin or the flake trigger. With
optical switches, they don’t have these problems because they’re triggered by light
signal.

Optical switches are easier to replace: An optical switch, as long as it’s the same
model, can be easily replaced. Mechanical switches on keyboards, if they’re not hot-
swappable, need to be soldered in order to replace the switch.

60. Disadvantages of optical switches
At this point, the biggest drawback is probably the lack of variety compared to
mechanical switches. Mechanical switches is a very mature market, and after decades of
existence, there are a lot of custom players and different switch body customizations
available. In addition, there are more well-known mechanical switch manufacturers
than optical switches. Optical switches are a newer technology, so the options available
on the market are fewer. In most optical switch production factories, there are some
differences, but not necessarily a brand of products, compatible with another.


However, there are also some downsides to optical keyboards. Additionally, optical
keyboards are generally more expensive than mechanical keyboards. However,
they also don’t support hotswap, thus users will be locked into a specific switch, unlike
mechanical keyboards.

61. Advantages in optical switches
•Optical communications use light to achieve high-speed, large-volume communications.
•This type of communication also requires high speed when switching between communication paths.
•Electronic switches can be used for fast, reliable switching, but this requires the optical signal to be converted to
an electrical signal, travel through the switch, and be converted back into an optical signal. This creates a
bottleneck of data at each switch and the advantages of optical communication become diminished.
•Optical switches can split or re-route specific bits of data quickly and reliably, without the need for converting
the signals to electrical signals.
•Optical switches not only allow for high-speed switching, but they also increase the stability of optical
communications.
• Optical switches are indispensable components for the stability and maintenance of high-speed, large-capacity
optical communication systems.

62. How Does Optical Switch Work


The optical switch is a technology that operates on fiber optic circuit to work similar to
traditional electrical network switches. The optical switch we mainly mentioned here is
operated by mechanical means which physically move fiber or other bulk optic elements.
For example, the opto-mechanical switch redirected an optical signal by moving fiber by
means of a mechanical device are typically stepper motor driven. It move a mirror(prisms,
or directional couplers) that directs the light from the input to the desired output.

63. Spatial light modulator (SLM) is an optical device that imposes some form of
spatially varying modulation on a beam of light. A simple example is an overhead
projector transparency. Usually when the term SLM is used, it means that the
transparency can be controlled by a computer. In the 1980s, large SLMs were placed
on overhead projectors to project computer monitor contents to the screen. Since
then, more modern projectors have been developed where the SLM is built inside
the projector. These are commonly used in meetings for presentations.
•Usually, an SLM modulates the intensity of the light beam. However, it is also
possible to produce devices that modulate the phase of the beam or both the
intensity and the phase simultaneously.
•SLMs are used extensively in holographic data storage setups to encode
information into a laser beam similarly to the way a transparency does for
an overhead projector. They can also be used as part of a holographic display
technology.
•SLMs have been used as a component in optical computing. They also often
find application in holographic optical tweezers.
•Liquid crystal SLMs can help solve problems related to laser microparticle
manipulation. In this case spiral beam parameters can be changed dynamically

Schematic of liquid crystal-
based Spatial Light
Modulator. As liquid
crystals are birefringent,
applying a voltage to the
cell changes the effective
refractive index seen by the
incident wave, and thus the
phase retardation of the
reflected wave.
Spatial Light Modulators

65. Schematic of a liquid crystal-based Spatial Light Modulator. As liquid crystals are
birefringent, applying a voltage to the cell changes the effective refractive index seen by
the incident wave, and thus the phase retardation of the reflected wave.
A spatial light modulator (SLM) is an
optical device that imposes some form
of spatially varying modulation on a
beam of light.
Spatial Light Modulators

66. Spatial light modulator (SLM) is a general term describing devices that are used to
modulate amplitude, phase, or polarization of light waves in space and time.
Spatial Light Modulator systems are based on translucent (LCD) or reflective (LCOS)
liquid crystal microdisplays. This means that light is manipulated in order to obtain a
desired output, and SLM is commonly used in overhead projectors such as those used
in schools and office conference rooms.

A spatial light modulator is an electronically programmable device that can
modulate light output based on a specific fixed spatial pattern (pixel), essentially
projecting light that is controlled in either amplitude only, phase only or both
(phase-amplitude). This device makes use of liquid crystals to modulate the light,
which is why overhead projectors are called LCD projectors.
Spatial Light Modulators

67. There are many types of SLMs, and one common type is the electrically addressed SLM
(EASLM), wherein the image is created and changed electronically just like in most
electronic displays, and which usually receives input via conventional digital interfaces
such as VGA or DVI.


Another type is the optically addressed SLM (OASLM), which requires a separate light
input encoded with an image that it can then project on its surface, again using liquid
crystals. This means that an OASLM is a secondary display that takes input from an
EASLM. In a process called image tiling, the images produced with an EASLM are then
sequentially transferred to different parts of an OASLM before the whole image is
displayed for the viewers. This can result in high-resolution images above 100 megapixels.
Spatial Light Modulators

68. OASLM is normally less expensive and less complicated than electrically addressed SLM
(EASLM). More importantly, OASLM has its unique advantages over EASLM for the
application of holographic displays, such as the higher resolution, elimination of pixels
and associated dead space between pixels, which results in a large viewing angle and less
undesired diffraction patterns in the replay image..
Spatial Light Modulators

69. Holographic display
•A holographic display is a type of 3D display that utilizes
light diffraction to display a three-dimensional image to the
viewer. Holographic displays are distinguished from other
forms of 3D displays in that they do not require the viewer to
wear any special glasses or use external equipment to be able
to see the image, and do not cause the vergence-
accommodation conflict.
•In simple terms, hologram technology is a three-dimensional
projection which can be seen without using any special
equipment such as cameras or glasses. The image can be
viewed from any angle, so as the user walks around the display
the object will appear to move and shift realistically.
Holographic images can be static, such as a picture of a
product, or they may be animated sequences which can be
watched by multiple people from any viewpoint.
•Some commercially available 3D displays are advertised as
being holographic

70. Holographic display technology can reconstruct the same images of the original objects
exactly, which has become the goal of the three‐dimensional display.
Applications of LCs in Holographic Display
As liquid crystal devices can modulate the polarization
state of light, they have been widely used in the
holographic display to modulate the phase and
amplitude of information. Among them, liquid crystal
spatial light modulator and liquid crystal lens are two
important devices in the holographic diffraction.

71. •Dynamic holographic display technologies based on LC photorefractive material have been also
studied.
•Lenses based on LC materials have the advantages of zoom function, short response, and no
mechanical movement.
•By controlling the voltage distribution of the corresponding electrode in the LC layer, the refractive
index distribution of the LC lens can be changed accordingly, so the distribution of the emitted light of
the pixel can be controlled easily.
•The LC lenses can be used not only to achieve 2D/3D conversion but also to realize holographic
reproduction. So, the LC lenses have also been widely used in the holographic display in order to
improve the quality of the reconstructed image.
•The LC light valve realizes the phase delay of light by controlling the refractive index of the LC
molecules. When the LC light valve is used in the holographic display, the light intensity of the
reconstructed image can be adjusted easily.
•In this way, desirable color holographic display can be achieved by adjusting the intensity of three
color images.
Applications of LCs in Holographic Display
LC‐SLM is one of the most important devices in holographic display. When the voltage is applied on
the LC‐SLM, the amplitude, phase, polarization state, and wavelength of light distribution can be
changed in space, so the incoherent light can be converted into coherent light.

72. PRINCIPLE OF HOLOGRAPHIC RECONSTRUCTION BASED ON SLM:

In holographic reconstruction, SLM is used to modulate the phase information of light. The molecular
arrangement of the LC phase is nematic, and its shape is similar to that of the filamentous type.
In the LC‐SLMs, the LCs have different modes of operation. For twist‐nematic mode, in the voltage‐off state,
the whole LC layer is arranged in a 90° distortion relative to the upper and lower substrates. Then the
polarization direction of the incident polarized light in the LC layer is twisted by 90° and the amplitude of
the incident light will be changed due to the birefringence.
In the voltage‐off state, the LC molecules are arranged vertically relative to the upper and lower
substrates. At this time, the LC layer has no distortion effect on the polarized light and the amplitude
of the incident light remains unchanged.

For the electronically controlled birefringence mode, the angle between the polarization direction of the
incident polarized light and the long axis of the LC molecules is caused when the voltage is applied to
change the direction vector of the LC molecules. Then the incident polarized light undergoes
birefringence and the amplitude changes accordingly. In addition, there are other operation modes
such as vertical alignment. When the operation mode of the LC changes, the modulation capability of the
SLM changes accordingly.
Applications of LCs in Holographic Display

73. Applications of LCs in Holographic Display
•As liquid crystal (LC) can modulate the polarization state of the light, LC devices have been widely
used in the holographic display to modulate the phase and amplitude of information.

74. Applications of LCs in Holographic Display
•As liquid crystal (LC) can modulate the polarization state of the light, LC devices have been widely
used in the holographic display to modulate the phase and amplitude of information.

75. Applications of Holography
In healthcare industry
•Doctors and patients alike will benefit from radical new
applications of holograms in the medical industry. The type
of data provided by modern imaging techniques such as MRI
and CAT scans can be easily translated into digital
information. Traditionally, doctors have viewed this data on
computer screens in 2D slices. Medical hologram technology
will allow a complete 3D visualisation of internal organs and
body parts. This will allow doctors a greater ability to
examine diseases and injuries in individual patients and will
lead to more accurate diagnoses.

76. Applications of Holography
•Holographic entertainment is no longer simply a science fiction dream. One of the most
visible applications of this technology in recent years has been its use in concerts. Stars from
the past can be resurrected to perform once again, and even accompany modern artists live
on stage.
•These displays can also be used for live performances where the musicians are not physically
present, instead transmitting their image to appear before the audience.
Acer Laptop With Holographic
Display
Holographic Projection and Virtual Reality
Video Production
Mobile Holographic Display

77. Applications of Holography
•In gaming
In the area of gaming, holographic technology is
being used by developers to create realistic characters.
Surrounding a subject with cameras and sensors allows the
developers to capture photorealistic models which then
appear in their games. The cameras take shots of the subject
from lots of angles, which means the models that appear in
the game are fully 3D and interactive.
•In the classroom
One of the most exciting applications of holograms is
the improvement of the educational experience. In order to
engage students more fully, interactive digital lessons will be
used in schools. This combination of digital and real-world
information is known as mixed reality.
Complex subjects can be taught using holographic images
that students can interact with and examine. For example,
pupils can virtually explore the ruins of an ancient building
during history lessons, or observe individual atomic particles
and how they behave.

78. Optical tuning refers to the ability to control or adjust the properties of optical components, such as
lenses, mirrors, filters, and other optical elements, in order to change their behavior or performance.

By leveraging the tunability of liquid crystals and the effect of the refractive index of the
environment on SLRs, the optical response of the array can be controlled electrically by switching
between states in the liquid crystal.

Liquid crystals (LCs) are one of the key materials used in light beam manipulation, as their
pronounced anisotropy and fluidity allow their refractive index to be tuned by small applied
voltages. One remarkable feature of these materials is their high versatility.


Optical Tuning

79. Data processing refers to the manipulation and transformation of data into a more usable or
informative form. It involves a series of operations or steps that are performed on data to extract, organize,
analyze, and present it in a meaningful way.

LC in Data Processing:
Liquid crystals play a significant role in data processing, particularly in certain types of displays and optical
devices. Liquid crystals are versatile materials that can be manipulated to control the properties of light.
Their applications in data processing are widespread, impacting fields such as displays,
telecommunications, imaging, and optical measurement systems.
Data processing