FEMTOSECOND DEFLECTION SPECTROSCOPY - A NOVEL METHOD TO PROBE CARRIERTRANSPORT IN SEMICONDUCTORS

Time and space resolved measurements of a test beam deflection Delta T heta ill the far-field after excitation of GaAs at 300 K with 30 to 10 0 fs pump laser pulses are presented as a novel method to observe carr ier dynamics in a semiconductor. We show that after electron-hole-pair excitation the test beam deflection at a delay time tau is caused by a lateral inhomogeneous change of the extinction coefficient Delta kap pa(tau) in a surface near region. We compare the Delta Theta(tau) meas urements to simultaneously measured intensity changes Delta T(tau) of the transmitted rest pulses, which are sensitive to Delta kappa(tau) a veraged over the sample thickness. Significant differences between Del ta Theta(tau) and Delta T(tau) are interpreted in the framework of bal listic transport of tile carriers from highly excited surface near reg ions into deeper regions of tile sample.