CARS difference spectroscopy. I—theory for binary mixtures

Abstract

The theory for CARS difference spectroscopy is developed. This is an extension of linear Raman difference spectroscopy to non-linear methods. This technique can be applied to the study of frequency shifts and band width changes in the CARS spectra of liquid mixtures or solutions when fluorescence does not allow linear Raman difference spectroscopy to be used. However, because of their coherent properties CARS spectra show complex line shapes due to interference effects between adjacent lines, which prohibits the simple subtraction of CARS spectra from one another. To make use of this technique, the spectra must be simulated with the inclusion of interference terms. The necessary theoretical treatment is outlined and some numerical model calculations for the v2(A Raman modes in chloroform4euterochoroform mixtures of different concentrations are given. Special emphasis is put on illustrating the influence of the interference effects in the CARS spectra of these mixtures.