Second-harmonic Efficiency and Reflectivity of GaAs During Femtosecond Melting

Abstract

Studies of the ultrafast melting of semiconductor surfaces under intense laser irradiation at frequencies above the bandgap reveal changes in the dielectric properties on the sub-picosecond timescale. Reflectivity measurements of silicon with femtosecond pulses demonstrate significant changes within 300 fs.1 Second-harmonic measurements on silicon further show that the top 70-130 Å of the silicon surface loses its cubic symmetry within 150 fs.1 In this paper we report on simultaneous reflectivity and second-harmonic generation (SHG) measurements during the melting of GaAs with 160-fs laser pulses. The results show bulk melting to a depth of at least 90 atomic layers within the pulsewidth.