2-PHOTON PHOTOELECTRON-SPECTROSCOPY OF GAP(110) AFTER SPUTTERING, ANNEALING, AND MULTISHOT LASER DAMAGE

Two-photon photoelectron spectra of Cap have been measured using 3-ps laser pulses of a photon energy below the valence-band photoelectron t hreshold. Clean, 1x1 ordered GaP(110) surfaces and surfaces disordered by Ar+ sputtering are compared. Delayed excitation/probe measurements set an upper limit of 3 ps on the relaxation time of transiently popu lated states. Changes in the photoemission spectra have been observed following pulsed-laser irradiation of surfaces with photon energies le ss than the band gap, and fluences below the threshold of single-shot damage. The changes in the spectrum are discussed with reference to pr evious studies of laser-induced desorption and damage on Gap.