PHOTOCURRENT AUTOCORRELATION OF FEMTOSECOND LASER-PULSES IN POLY(P-PHENYLENEVINYLENE)

Photoconductive thin-film cells made from a pi-conjugated polymer, pol y-(p-phenylenevinylene) (PPV) can be used for diagnostics of femtoseco nd laser pulses utilizing the phenomenon of photocurrent autocorrelati on. In general, the autocorrelation photocurrent signal can be due to the nonlinearity of the primary photogeneration step or to the influen ce of the existing photogenerated charge carriers on the efficiency of production of further amounts of charges. Experiments with 150 femtos econd pulses from a Ti-sapphire laser at 800 nm show that two-photon i nduced photocarrier generation is the nonlinear process leading to the autocorrelation in PPV photoconductive cells. There is no indication of the presence of any photogeneration intermediates with picosecond r ange lifetimes.