LASER RAMAN SPECTROSCOPY WITH DIFFERENT EXCITATION SOURCES

IN THIS PRESENTATION I HAVE DISCUSSED ABOUT LASER RAMAN SPECTROSCOPY,ITS PRINCIPLE,WORKING, CONSTRUCTIO AND APPLICATIONS..

1. LASER RAMAN SPECTROSCOPY WITH DIFFERENT EXCITATION SOURCES Presented By:- PRAVEEN SONI CSJMA18001390318

2. CONTENTS 1 .WHAT IS SPECTROSCOPY? 2 .WHAT IS SCATTERING OF LIGHT? 3 .RAYLEIGH AND RAMAN SCATTERING 4 .STOKES AND ANTI STOKES SCATTERING 5 .INTRODUCTION TO RAMAN SPECTROSCOPY 6 .PRINCIPLE OF RAMAN SPECTROSCOPY 7 .SOURCES USED IN RAMAN SPECTROSCOPY BEFORE LASERS AND THEIR DISADVANTAGES 8 .ADVANTAGES OF LASER IN RAMAN SPECTROSCOPY

3. 09 .COMPONENTS OF LASER RAMAN SPECTROSCOPY 10 .SCHEMATIC DIAGRAM OF RAMAN SPECTROSCOPY 11 . THE SOURCE 12 .SOME COMMON LASER USED IN RAMAN SPECTROSCOPY 13 .SAMPLE ILLUMINATION SYSTEM 14 .SPECTROMETER 15 .DETECTOR 16 .DIFFERENCE BETWEEN RAMAN AND IR SPECTROSCOPY 17 .APPLICATIONS 18 .REFERENCES

4. WHAT IS SPECTROSCOPY? Spectroscopy is the study of the interaction between matter and electromagnetic radiation as a function of the wavelength or frequency of the radiation. Spectroscopy is used as a tool for studying the structures of atoms and molecules. The first spectroscope was invented in 1814 by the physicist and lens manufacturer Joseph Von Fraunhofer .

5. WHAT IS SCATTERING OF LIGHT? When radiation passes through a transparent medium ,the species present in that medium scatter a fraction of beam which is termed as scattering of light.

6. RAYLEIGH AND RAMAN SCATTERING Rayleigh Scattering It is a elastic scattering phenomenon when radiation interacts with matter. In this type of scattering the energy of the scattered photons is same as that of the incident photons after interacting with matter. Raman Scattering It is a inelastic scattering phenomenon when radiation interacts with matter. In this type of scattering the energy of the scattered photons is not same as that of the incident photons after interacting with matter.

7. STOKES AND ANTI STOKES SCATTERING Stokes Scattering In this type of scattering the frequency of the emitted radiation is lower than the incident radiation. Anti Stokes Scattering In this type of scattering the frequency of the emitted radiation is higher than the incident radiation .

8. INTODUCTION TO RAMAN SPECTROSCOPY Raman Spectroscopy was discovered by Chandrasekhara Venkata Raman in 1928. Raman Spectroscopy is a spectroscopic technique mainly used to observe vibration, rotational and other low frequency modes in a system. Raman Spectroscopy is a popular technique because it is non-destructive and in principles require no sample preparation. This technique is commonly used in chemistry to provide a fingerprint by which molecules can be identified. Raman Spectroscopy is the measurement of the wavelength and intensity of inelastically scattered light from molecules.

9. PRINCIPLE OF RAMAN SPECTROSCOPY Monochromatic radiation is passed through the sample such that the radiation may get reflected, absorbed or scattered. The scattered have a different frequency from the incident photon as the vibration and rotational property vary. This results in the change of wavelength which is studied in the IR spectra. The difference between the incident photon and the scattered photon is known as the Raman Shift.

10. SOURCES USED IN RAMAN SPECTROSCOPY BEFORE LASERS AND THEIR DISADVANTAGES Commonly used sources before the invention of lasers were 435.8nm and 253.6nm emission lines of mercury lamps. Disadvantages that occurs were:- 1. The source is an extended one and the brightness available per unit area is very small. 2. The relative high frequency of mercury radiation often causes the sample to fluorescence. 3. As coloured samples absorb in this high frequency region, it is not possible to record their spectra.

11. ADVANTAGES OF LASER IN RAMAN SPECTROSCOPY Excellent monochromaticity. Good beam focusing capabilities and small line widths. The second order Raman spectra could be recorded. The broadening due to doppler’s effect could be minimized .

12. COMPONENTS OF LASER RAMAN SPECTROSCOPY The major components in a Laser Raman Spectrometer are- 1. A source of monochromatic radiation 2. Sample illumination system 3. Spectrometer 4. Detection System 5. Computer

13. SCHEMATIC DIAGRAM OF RAMAN SPECTROSCOPY

14. THE SOURCE Lasers are used as photons sources due to their highly monochromatic nature, and high beam fluxes. The Helium-Neon Laser emits highly monochromatic light at 632.8nm The Helium-Neon Laser is a commonly used excitation source used in the modern Raman Spectrometers .

15. SOME COMMON LASER SOURCES USED IN RAMAN SPECTROSCOPY

16. SAMPLE ILLUMINATION SYSTEM Liquid Samples Water is regarded as good solvents for the study of inorganic compounds in Raman Spectroscopy because water is a weak Raman scattered but a strong absorber of infrared radiation . Solid Samples Raman spectra of solid samples are often acquired by filling a small cavity with the sample after it has been ground to a fine powder. Gas Samples Gases are normally contained in glass tubes 1-2cm in diameter and about 1mm thick. Gases can also be sealed in small capillary tubes .

17. SPECTROMETER It disperses Raman Scattered light. A polychromator with a diffraction grating is typically used. It is used for recording or measuring Raman spectra, especially as a method of analysis. Now, Raman Spectrometer being marketed are either Fourier transform instruments equipped with cooled germanium transducer or multichannel instruments based upon charged coupled device.

18. DETECTORS Detectors are used to detect the signals obtained from the spectrometer. Researchers traditionally used single points detector such as Photocounting or Photomultiplier(PMT). Now a days Multichannel detectors like Photodiode Arrays(PDA) and Charged Coupled Devices (CCD) are used because they have very high sensitivity and performance .

19. DIFFERENCE BETWEEN RAMAN AND IR SPECTROSCOPY RAMAN SPECTROSCOPY Water can be used as solvent. Accurate but not very sensitive. Optical system are made of quartz and glass. It is due to the scattering of light by the vibrating molecules. IR SPECTROSCOPY Water cannot be used as solvent because it is opaque to infrared radiation. Accurate and very sensitive. Optical system are made of special crystals such as CaF2 and NaBr etc.. It is due to the absorption of light by the vibrating molecules.

20. APPLICATIONS OF RAMAN SPECTROSCOPY It is used to characterize materials, measure temperature and find the crystallographic orientation of the samples. As a means to detect explosives for airport security. Used in medicine, aiming to the development of new drugs and in the diagnosis of arteriosclerosis and cancer. Contaminant Identification. Pharmaceuticals and cosmetics. Provides a fingerprint by which molecule can be identified.

21. REFERENCES BOOKS 1.R L LAKSH,(2004) INFRARED IN RAMAN SPECTROSCOPY, RAJAT PUBLICATION. 2.M C TOBIN,(1996) LASER RAMAN SPECTROSCOPY,WILEY PUBLICATION. WEBSITES https://www.horiba.com/ (FOR RAMAN SPECTROSCOPY PRINCIPLE) http://www.osa-opn.org/ (FOR RAMAN SCATTERING AND ITS EFFECT) https://www.ulsinc.com/ (FOR LASERS AND ITS ADVANTAGES)