Raman Spectroscopy

Abstract

In this chapter we consider the scattering of photons with energies of the order of 2 to 4 eV by optical phonons. When the spectrum of the radiation scattered by the crystal illuminated with monochromatic light of frequency ω _L is analyzed, it is found that it consists of a very strong line at the frequency ω _L , as well as of a series of much weaker lines with frequencies ω _L ±ω _j (q), where ω _j (q) are optical phonon frequencies (Fig. 3.1). The strong line centered at ω _L is due to elastic scattering of photons and is known as Rayleigh scattering. The series of weak lines at ω _L ±ω _j (q), where ω _j (q) originates from inelastic scattering of photons by phonons and constitutes the Raman spectrum. The Raman bands at frequencies ω _L −ω _j (q) are called Stokes lines, those at frequencies ω _L +ω _j (q) are known as anti-Stokes lines. The intensities of the anti-Stokes lines are usually considerably weaker than those of the Stokes lines.