PHASE-TRANSFORMATIONS OF AN INSB SURFACE-INDUCED BY STRONG FEMTOSECOND LASER-PULSES

Phase transformations of InSb(211) induced by 130-fs laser pulses at 8 00 nm have been time resolved in a wide range of laser fluences. The p ump-probe technique has been used, where bath optical reflectivity and reflected second-harmonic generation (SHG) from the probe pulses are monitored as functions of probe versus pump pulse delay. The results a re indicative of InSb undergoing a phase transition to a centrosymmetr ic state in a few hundred femtoseconds at sufficiently high laser flue nces, similar to GaAs studied earlier. The initial ultrafast drop of t he second-harmonic signal following excitation in the high-fluence reg ime occurs within the same time interval for both InSb and GaAs, sugge sting that these changes are governed by electronic excitation effects . Subsequent studies of the InSb sample surface morphology and of the reflectivity imply the formation of an amorphous layer on the surface following laser-induced melting. It is argued that a metastable metall ic phase does not appear on the surface of InSb under femtosecond lase r excitation at room temperature.