Effect of homogeneous and inhomogeneous broadening on resonance CARS excitation profiles

The influence of broadening due to intrinsic molecule and ensemble properties (homogeneous and inhomogeneous broadening) on resonance CARS excitation profiles (CEPs) was investigated by means of a theoretical model. The non‐linear susceptibility χ (3) of a homogeneous ensemble of molecules was derived from perturbation theory using a Franck—Condon model and applying a crude Born—Oppenheimer approximation. Then it was assumed that these molecules are situated in an inhomogeneous environment which changes their electronic energies. The CARS intensity for this inhomogeneous ensemble was obtained from the homogeneous CARS intensity taking into account a distribution of energies. The influence of homogeneous and inhomogeneous broadening on CEPs was demonstrated by model calculations and compared with results obtained for resonance Raman excitation profiles. Possible applications are discussed.