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.

© 1990 Optical Society of America