Time evolution of excited-state nonlinear optical processes in conjugated linear chains

The enhancement of the third order nonlinear optical susceptibility in diphenylhexatriene (DPH) when the system is optically pumped into /spl Pi/electron excited states, has been studied theoretically and experimentally. In this report, the time evolution of the excited state enhanced is experimentally studied using picosecond degenerate four wave mixing (DFWM) techniques, in which DPH molecules are optically pumped to their excited state, and then nonresonantly probed.