Second harmonic generation in reflection from crystalline GaAs under intense picosecond laser irradiation

Abstract
The emission of second harmonic radiation in reflection from crystalline GaAs irradiated with 20-ps, 530-nm laser pulses has been measured for incident laser fluences far exceeding the threshold fluence Fth for permanent reflectivity changes. The results are consistent with the occurrence of surface melting during the laser pulse. Detailed analysis of the second harmonic signals reveals an upper limit of 2 ps for the structural transition associated with the melting of the surface.