EXPERIMENTAL-OBSERVATION OF ENHANCED NONRESONANT NONLINEAR OPTICAL-RESPONSES FROM OPTICALLY PUMPED ELECTRONIC EXCITED-STATES

Enhancement of greater than 2 orders of magnitude of nonresonant third-harmonic generation from an optically pumped S1 electronic excited state is experimentally observed for quasi-two-dimensional conjugated disklike structures. The isotropically averaged S1 excited-state microscopic susceptibility <gamma(s1)(-3-omega;omega,omega,omega)> is - 1640 +/- 100 x 10(-36) esu, and the corresponding macroscopic chi-s1(3)(-3-omega;omega,omega,omega) exhibits temporal decay and pump-power saturation behavior associated with the expected decay and saturation of the S1 state. The enhancement mechanism through optical pumping followed by a non-resonant nonlinear optical probe is generalizable to both second- and third-order optical processes in nonlinear optical media.