6-WAVE MIXING SPECTROSCOPY - RESONANT COHERENT HYPER-RAMAN SCATTERING

A theoretical description of the six-wave mixing spectroscopy is prese nted. The six-wave mixing spectroscopic signals in time and frequency domains are expressed in terms of the fifth-order nonlinear response f unctions. Particularly, the resonant coherent hyper-Raman scattering w ith wave vector of 4k(1)-k(2) and frequency of 4 omega(1)-omega(2), wh ere 2 omega(1) approximate to omega(2) is discussed by invoking the op tical Bloch approximation. The coherent anti-Stokes hyper-Raman scatte ring (CAHRS) susceptibility is found to be very similar to that of CAR S. The dephasing-induced vibrational resonance in the excited state is also manifest in this experimental configuration. By making a direct comparison of CAHRS signal with that of CARS, it is found that the rat io of CAHRS to CARS susceptibilities provides a crucial information on the permanent dipole moment of the excited state in either gas or con densed phases. It is briefly discussed that this method can be of use in estimating the molecular hyperpolarizability. (C) 1998 American Ins titute of Physics. [S0021-9606(98)01710-3].