Relaxation of highly excited surface states of silicon probed by time-resolved optical second-harmonic generation

Electronic excitation and relaxation processes on semiconductor surfaces have been investigated intensively with time resolved two-photon photoemission. 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.