Ripples and grain formation in GaAs surfaces exposed to ultrashort laser pulses

The damage morphology of GaAs1 0 0 single crystal following femtosecond laser (wavelength 806 nm, pulse duration 110 fs, prf 10 Hz) excitation was studied as a function of laser fluence and number of pulses. The threshold value for damage to occur in a GaAs surface in the present experiment was 1.3×10¹⁴ W/cm² for a single pulse. The cooling rate for threshold fluence was calculated as 2.22×10¹⁴ °C/s. The damage occurred in the form of surface removal. Ripples and grains were formed in the removed surface. At higher fluences micron depth pits were also formed. The damage morphology was explained with the help of Boson-condensation hypothesis.