Abstract

An intense femtosecond pulse of visible light incident on the surface of a crystalline semiconductor can deposit energy in the electronic system in a time that is short compared to the electron–phonon coupling time. If the density of deposited energy is high enough, a layer of material at the surface may be able to disorder before appreciable energy is transferred from the electrons to the ions of the lattice.¹ Pump–probe experiments on silicon rising 90-fs pulses showed a rise in reflectivity and a decay in second-harmonic generation (SHC) consistent with the melting of the surface layer after the excitation pulse^2–4 Because the intensity of the reflected second-harmonic signal depends on crystallographic orientation, its decay serves as a sensitive probe of structural changes. GaAs offers the advantage offers SI that SHG is dipole-allowed in the bulk, so that the surface contribution is negligible compared to the strong bulk signal.

© 1992 Optical Society of America