Chemical analysis by laser-based Raman spectroscopy

Abstract

Raman was first discovered by C.V. Raman and K.F. Krishnan in 1928.It is a spectroscopic technique based on inelastic scattering of monochromatic light usually- from a laser in the visible or near infra-red part of electromagnetic spectrum. It probes vibrational, modes of the molecule and crystals of solid, liquid, and gaseous samples. t is commonly used in chemical analysis to provide a fingerprint by which molecules can be identified. At the time of its discovery from observing sunlight, obvious challenges were posed by the lack of a good Raman source, lack of a good detector, and by interference from fluorescence, which in some cases overwhelmed the Raman signal. The advent of laser made good for the deficiency of a good Raman source, multichannel detectors like Photodiode Arrays (PDA) or Charge - Coupled Devices (CCD) for a good detector and Fourier –transform for fluorescence. In addition, instruments such as notch filters, tunable filters, laser stop apertures, double and triple spectrometric systems are now used to reduce Rayleigh scattering and obtain high-quality Raman spectra. Thus, Raman has become the optimal technique for versatile, minimally invasive spectroscopy.