Pulsewidth-dependence of nonlinear energy deposition and redistribution in Si, GaAs and Ge during 1 μm picosecond irradiation

Abstract

We have used 1 μm pulses ranging in duration from 4–260 ps to measure the pulsewidth dependence of the nonlinear absorption, melting threshold, and resolidification morphologies of Si, GaAs, and Ge. With these materials, we have been able to quantify a variety of nonlinear absorption processes with a single excitation wavelength. We find that the fluence required to melt Si and GaAs is roughly proportional to the square root of the pulsewidth while that required for Ge is nearly pulsewidth independent. A crystalline-to-amorphous transition is observed in Si for pulses less than 10 ps and in GaAs for all pulsewidths, but no such transition is observed in Ge. These observations are shown to be consistent with the various energy deposition and redistribution mechanisms present in each material. Finally, we have used the active nonlinearities in Si and GaAs to construct optical limiters designed to protect sensitive optical components from intense 1 μm radiation.