MEASUREMENT OF RELAXATION-TIMES OF EXCITED MOLECULES BY METHODS OF RESONANCE WAVE MIXING

Nondegenerate four-wave mixing (FWM) is considered in a medium in whic h frequencies of one pair of interacting light waves are resonant with the absorption band, while frequencies of two other waves ate resonan t with the fluorescence band (two-resonance FWM). Based on calculation s performed for homogeneous and inhomogeneous bands, it was concluded that the nonlinear cubic susceptibility chi((3)) of a system is highly sensitive to the relation between frequency detuning of the pumping w aves and the energy relaxation rate. The possibilities of four-wave an d three-wave mixing in studies of molecular photodynamics are compared . It is shown that ultrafast relaxation between levels of the excited or ground electronic states of molecules can be selectively studied by combining resonance conditions upon four-wave mixing.