Linear and nonlinear optical reflection in pulsed laser melting of a crystal lacking a center of symmetry

A thermal model is used to interpret experiments on probe-radiation reflection and second-harmonic generation SHG in reflection when a short laser pulse acts on GaAs. A formula is derived for SHG in reflection for the case where there is a layer of liquid of thickness d at the surface. Numerical calculations have been performed on the time dependence of d, the linear reflection coefficient, and the SHG for the probe radiation. There is good agreement between theory and experiment which supports the thermal model for laser annealing.