LASER RAMAN SPECTROMETER (LRS)

LASER RAMAN SPECTROMETER (LRS)

Raman spectroscopy, as the name suggests is based on the Raman Effect discovered by the Indian physicist, Sir Chandrashekhar Venkata Raman (C. V. Raman) in 1928. Raman Effect takes place when monochromatic light (usually a visible laser) strikes a molecule and interacts with the bonds of that molecule. While most of the incident laser light scatters and produce no useful information (known as Rayleigh scattering), some of the light is re-emitted, which is shifted to longer wavelength with a loss of energy, known as 'Stokes radiation'. This shifted or stokes radiation produces a characteristic spectra or pattern of peaks, which can be considered as a 'fingerprint' for that substance. 

Raman spectroscopy complements the infra red spectroscopy very well and provides useful information where FTIR fails to answer many questions. It is fast and non-destructive method of analysis without any sample preparation. In addition to the H2O or CO2 content of the sample, it also identifies the chemical groups irrespective of the thickness of the sample and without taking a powder on the sandpaper. 
Schematic principle of a typical Raman Spectrometer

A typical Raman spectrometer unit contains:- 

1) laser excitation source, of various wavelengths (in nanometres) such as 325, 488, 514, 532, 785, 1064, etc with controls to adjust the power.

2) an optical microscope, used to adjust and focus the laser on the sample for analysis.

3) spectrometer, for high resolution analysis of light, once it has interacted with the sample.

4) raman box, consisting of a series of lens and filters to restrict unwanted light to the sample and from sample to the spectrometer.

5) computer and software, for processing the incoming signals and presenting the data in a graph form.

Because of the use of powerful microscope, Raman spectroscopy can be performed on very small surfaces of micron sizes and hence it provides a versatile application in various gemmological analyses. It not only presents the information about the host mineral, but also inclusions present in it, or the various layers within, as in case of composites, or colour zoning, and much more. It proves to be very useful in case of large specimens or gems set in a jewellery, or when the size of stones are too small to conduct standard gemmological tests, or if the sample is in rough form. The spectra thus obtained are carefully compared with the database to draw the results. A detailed and comprehensive database is always required to carry out a successful Raman analysis. 


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