Carrier thermalization, cooling and diffusion in InSb through a nonlinear pump-probe technique

We investigated the ultrafast carrier dynamics in InSb using a nonlinear pump-probe technique. The measurement involves two pump pulses chopped at different frequencies and the detection of the probe modulation at their sum frequency. We show that the nonlinear signature and dynamics of the transmission-bleaching signal enables the differentiation of carrier thermalization from cooling dynamics. We follow the evolution of the injected carrier distribution from a nonthermal to a thermal one and calculate its absolute temperature and energy decay rates as a function of time from a single transmission pump-probe measurement. The carrier scattering rate in the thermalization stage increases by (3 ps)-1 with doubling the injected carrier density. For an initial injected excess energy of 650 K, carrier thermalization is complete after 1.7 ps with a thermal distribution of 370 K. We also demonstrate the ability to follow carrier diffusion through the decay of the carrier grating decay in a transmission measurement. (C) 2004 American Institute of Physics.