Abstract

Electronic excitation and relaxation processes on semiconductor surfaces have been investigated intensively with time- resolved two-photon photoemission (2PPE).^1,2 Here, we report the first successful application of surface second-harmonic generation (SHG) for this purpose. The advantage of a purely optical technique is the possibility to extend the experiments to the high excitation regime where strong multi-photon absorption and the build-up of space charges hinder the spectroscopy of photoelectrons. In our studies the usual difficulty of identifying the exact origin of the observed changes of the nonlinear optical response is overcome by correlating the SHG pump-probe features with a systematic variation of the oxygen coverage of well characterized 7 × 7-reconstructed Si(111) surface and with the results of spectroscopic SHG measurements.

© 1996 Optical Society of America