Observation of dynamical interactions between σ- and π-electrons in organic molecules by resonant coherent-grating and coherent anti-Stokes Raman spectroscopy

Depending on the excitation pulse durations of 4–6 ps, we measured the remarkable alterations in the electronic resonant coherent population grating (CPG-type 1), coherent difference frequency grating (CG-type 3) and coherent anti-Stokes Raman scattering spectra of cresyl viole in ethanol. In case of the excitation with the shorter 4 ps pulses, the CPG-type 1, CG-type 3 and CARS spectra being composed of the multiple electronic resonances showed the specific light-induced enhancement coupled with the dominant normal vibration. The basis of these third-order nonlinear responses is most likely to be explained in the framework of the dynamical interactions between σ and π electrons.