Ultrafast response in optical nonlinearity of MBE grown GaAs/AlAs MQW and bulk GaAs

Summary form only given. Time evolution of the optical transmission spectra in GaAs and its quantum well following femtosecond excitation shows an increase in transmission at an energy close to the excitation energy. This is spectral hole burning resulting from the initial nonthermal distribution of photoexcited carriers. This nonthermal distribution thermalizes in a time on the order of 200 fs. Although this fast response is very attractive, no application has been tried mainly because it is followed by a rather slow response (1-100 ps) due to cooling through carrier-phonon interaction and the band filling effect. In the present paper, two methods are studied experimentally to reduce this slow response component. Measurements are carried out at room temperature by the degenerate pump-probe method utilizing tunable 200 fs-width, 82 MHz repetition pulses from a titanium sapphire laser.