Raman spectroscopy

raman-spectometer

Introduction to Raman spectroscopy

Raman spectroscopy was named in the honor of its inventor, C.V. Raman. Raman spectroscopy (RS) is a versatile method for analysis of a wide range of samples. It resolves most of limitations of other spectroscopic techniques. It can be used for both qualitative as well as quantitative purpose. Qualitative analysis can be performed by measuring the frequency of scattered radiations while quantitative analysis can be performed by measuring the intensity of scattered radiations.

Basic principles and instrumentation

Raman spectroscopy is a device using scattering technique. It is based on Raman Effect, i.e., frequency of a small fraction of scattered radiation is different from frequency of monochromatic incident radiation. It is based on the inelastic scattering of incident radiation through its interaction with vibrating molecules.

In Raman spectroscopy, by varying the frequency of the radiation, a spectrum can be produced, showing the intensity of the exiting radiation for each frequency. This spectrum will show which frequencies of radiation have been absorbed by the molecule to raise it to higher vibrational energy states.
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When Light hits a sample, It is Excited, and is forced to vibrate and move. It is these vibrations which we are measuring.
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A typical Raman System

raman-spectometer

A typical Raman System is mainly divided into two parts simply input system and output system.In input system mainly consists of Excitation sourse, Beam expander , Rayleigh filters ,Focusing mirror.

Excitation sourse : – Excitation sourse producing input rays for making excitation in solution for causing raman effect .

Beam expander :- Beam expanders are optical devices that take a collimated beam of light and expand its size.

Rayleigh filters :- These optical components are placed in the Raman beam path, and are used to selectively block the laser line (Rayleigh scatter) whilst allowing the Raman scattered light through to the spectrometer and detector.

Focusing mirror :- As that name indicates its foccusing the input and output light to Rayleigh filter / Solutions.

Input working :- Excitation sourse producing input rays for making excitation in solution for causing raman effect .This input rays passes through the beam expander for improving or expanding the beams after that its going to reyleigh filter in this filter has not to much role in the passing of input rays.By the help of foccusing mirror rays goes to Sample solution.

Output Systems.

In otput system mainly consists of Focusing mirror, Rayleigh filters , Gratings, Focusing mirror , Detector.

Focusing mirror :- As that name indicates its foccusing the input and output light to Rayleigh filter / Solutions.

Rayleigh filters :- These optical components are placed in the Raman beam path, and are used to selectively block the laser line (Rayleigh scatter) whilst allowing the Raman scattered light through to the spectrometer and detector.That means some of output rays have same wavelength as input rays (Without ramen offect) thats rays will filtered by this Rayleigh filters.

Gratings :- A diffraction grating is an optical component with a periodic structure, which splits and diffracts light into several beams travelling in different directions.

Focusing mirror :- Here its foccusing the output light to detector.

Detector :- A CCD (Charge Coupled Device) is a silicon based multichannel array detector of UV, visible and near-infra light. They are used for Raman spectroscopy because they are extremely sensitive to light.

Output working :-
Output rays reflected from sample is focused to Rayleigh filter through focusing mirror. This filiter will block the laser line (Rayleigh scatter) whilst allowing the Raman scattered light through to the spectrometer and detector.That means some of output rays have same wavelength as input rays (Without raman effect).Filtered light will goes to gratings for splitings and diffractions of light into several beams.This splited beams will focused to detecor by focussing mirror.A CCD (Charge Coupled Device) is using as detector which is very sensitive to light. Using tis detector data it will producing a spectrum Named Raman spectrum its including intensity.

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Applications of Raman spectroscopy

1.Raman spectroscopy is commonly used in chemistry, since vibrational information is specific to the chemical bonds and symmetry of molecules. Therefore, it provides a fingerprint by which the molecule can be identified.

2.In solid-state physics, spontaneous Raman spectroscopy is used to, characterize materials, measure temperature, and find the crystallographic orientation of a sample.

3.Raman spectroscopy can be used to observe other low frequency excitations of the solid, such as plasmons, magnons, and superconducting gap excitations

4. Spatially-offset Raman spectroscopy (SORS), which is less sensitive to surface layers than conventional Raman, can be used to discover counterfeit drugs without opening their packaging, and for non-invasive monitoring of biological tissue
5. Raman spectroscopy can be used to investigate the chemical composition of historical documents such as and contribute to knowledge of the social and economic conditions at the time the documents were produced.
6. Raman spectroscopy is being investigated as a means to detect explosives for airport security.

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