ENHANCEMENT AND SUBPICOSECOND DYNAMICS OF OPTICAL NONLINEARITIES OF EXCITED-STATES - TRANS-STILBENE IN SOLUTION

Using degenerated four wave mixing techniques and optical Kerr effect we studied the optical non-linearities of excited t-stilbene solution. Strong enhancement of the non-linear signal between the excited and g round states is observed and related to the third order non-linear sus ceptibility (chi((3))) taking into account resonance conditions. Sub-p icosecond studies of the chi((3)) dynamics show, depending on the expe rimental conditions, a fast decay time (in the range of < 1 ps) associ ated to electronic processes and a slower decay time (10-100 ps), depe nding on the solvent, associated with the reorientation time tau(or) o f the molecules in solution. We show that vibrational relaxation and s olvent cooling may control the dynamics of chi((3)).