Remarkable atomic population difference symmetry and coherence properties that are achieved without the custom laser-induced population inversion by the non-linear (Raman) saturated absorption spectroscopy are quantum mechanically explained and analytically modeled.
Top7.2. Stimulated Raman Effect
The Raman effect is a process of an inelastic interaction of electromagnetic radiation with quantum systems, after which the radiation is scattered, altering its frequency, and the quantum systems pass in other energetic states. The appearance of the Raman effect is related to the time variation of matrix elements of the induced electric dipole moment, calculated between two distinct states, k (initial) and n (final), of the scattering system, Figure 1, see Raman (1928), Harris & Bertolucci (1989), Singh (2002).
Figure 1. Symbolic representation of stimulated Raman scattering with cases: a) Rayleigh scattering; b) Stokes scattering; c) Anti-stokes scattering
Raman spectrum of a given macroscopic system consists of Raman Stokes – type lines and Raman anti-Stokes lines, much weaker than the first and symmetrical as them, in relation to the line having the same frequency as that of the incident radiation (Rayleigh line). The phenomenon that occurs to the excitation of a substance with a Laser radiation in high power pulsed and which consists in generating an intense radiation, coherent, well- directed, with the frequency equal to one of the normal frequencies of vibration of the substance is called the Raman stimulated effect. Is essential that the Width of the lines of the stimulated Raman stimulated radiation is much smaller than the one of the radiation lines that occurs in the effect of spontaneous.