Coherent phonon and electron spectroscopy on surfaces using time-resolved second-harmonic generation

pump (ω)E_probe ^*(ω)|E_probe(ω)|². This is much easier to detect than transient grating, photon echo, or four-wave mixing schemes that use higher-order nonlinearities. We have applied this technique to measure the energy gap and dephasing time of the dangling bond interband transition on the GaAs(110)-relaxed (1×1) surface. Surface-carrier/surface-phonon interaction plays an important and perhaps dominant role in surface carrier dephasing consistent with the larger electron-phonon coupling on the surface compared to the bulk. Received: 13 October 1998