Raman Spectroscopy:

Raman spectroscopy is a spectroscopic technique based on inelastic scattering of monochromatic light, usually from a laser source in the visible, near infrared, and near ultraviolet range.

Inelastic scattering means that the frequency of photons in monochromatic light changes upon interaction with a sample. Photons of the laser light are absorbed by the sample and then reemitted. Frequency of the reemitted photons is shifted up or down in comparison with original monochromatic frequency, which is called the Raman effect.

This shift provides information about vibrational, rotational and other low frequency transitions in molecules. Raman spectroscopy can be used to study solid, liquid and gaseous samples.

Raman Effect: Let us consider that a sample is irradiated with the monochromatic light (say laser) with the wavelength ranging between 300 and 1064 nm. The laser beam can be considered as an oscillating electromagnetic wave with electrical vector E and interacts with the polarizable electron density and the bonds of the molecule in the phase and induces electric dipole moment P = αE. This would deform molecules.