9.2 Raman Scattering: Basic Concepts
9.2.1 Stokes and Anti-Stokes Lines
When a beam of monochromatic light of frequency ω0 passes through a transparent medium (solid, liquid, or gas), the light scattered at right angles to the incident beam is found to contain, in addition to the original frequency, other frequency components. The spectrum of the scattered light shows a number of new lines situated symmetrically on both sides of the original line. This type of incoherent scattering was first observed in liquid by Raman in 1928 and is known as the Raman effect. Subsequently, the phenomenon was also observed in solids and gaseous media.
The satellite lines on the low-frequency (high-wavelength) side are called the Stokes lines, and those on the high-frequency (low-wavelength) side are known as anti-Stokes lines. Taken together, all these satellite lines are usually referred to as Raman lines.
The origin of the Stokes and anti-Stokes lines lies in the interaction between the incident photon of energy 
and quantized vibrational modes of energy 
in liquids or optical phonons of energy 
in crystalline solids.
Assume that a plane electromagnetic field described by
is present in the medium, ...
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