Transform relations for CARS excitation profiles

Abstract

PACS 33.20.Wr, 42.65.Dr The calculation of resonance CARS (coherent anti-Stokes Raman scattering) excitation spectra will be greatly simplified by applying the transform theory, which relates the scattering amplitudes to the recorded absorption spectrum. Based on transform relations, it is shown that the red shift of CEP arises due to the violation of the Condon approximation when the dependence of the electronic transition matrix element on the vibrational coordinates is taken into account. It leads to two competing mechanisms -a constructive interference (due to the non-Condon terms) in addition to the destructive interference (due to the Franck-Condon coupling) in the Raman amplitude. The interference of these two mechanisms can essentially affect the shape of the coherent Raman excitation profile. A simulation of the measured coherent excitation profile (CEP) of the resonance CARS of ZnPc in a polymer film is carried out.