Resonant absorption, Rayleigh scattering

Figure 17.2.7 Schematic views of Raman scattering. Excitation (E) to a nonstationary virtual state is followed by Rayleigh scattering (R ) with no change in energy, or Raman scattering (R and R2) with energy changes equal to vibrational quanta, (a) The normal Raman effect involves excitation in a nonabsorbing region, (b) The resonance Raman effect involves excitation very near an allowed absorption transition.

A comparison of Eq. (12.14) with Eq. (10.43) shows that the imaginary part of a a (the matrix element for resonance Rayleigh scattering) is proportional to the matrix element for ordinary absorption. The real part of can be related to the refractive index (Box 3.3 and [14]). 

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