Femtosecond fifth-order nonlinear response of nuclear motion in liquids investigated by incoherent laser light. Part II. Experiment

Abstract

A setup for detection of a fifth-order nonlinear Raman process based on incoherent laser light is developed, enabling the introduction of two independent delay times. Depending on phase matching conditions, interference of nonlinear processes of third- and fifth-order or a dominance of one of these processes can be obtained. Possibilities to distinguish between them are discussed and signals of fifth-order Raman-type processes are identified. Regarding the chosen time variable the delay curves are symmetric. Because the correlation time of the incoherent radiation is in the order of magnitude of the fast dephasing time in the liquids, a necessary deconvolution procedure is developed and applied to extract molecular data. A fast dephasing time obtained for nitrobenzene agrees with published data. In mixtures of nitrobenzene with trifluoroethanol the dephasing time decreases, additional excitation of an intramolecular vibration causes an increased effective dephasing times. Both effects could be simulated by independent molecular responses for both kinds of molecules or independent relaxation mechanisms, respectively. From the dependence of the measured FWHM times on the delay time between the two excitations, relations of two relaxation times can be deduced. This information is going beyond that obtainable from third-order coherent techniques.