ИСТИНА

Experimentally observed femtosecond laser-induced periodic surface structures (LIPSS) on amorphous hydrogenated silicon films (a-Si:H) were theoretically described using the Sipe model. The LIPSS with period of 1.20 ± 0.02 μm observed in the experiment change their ridges direction relative to laser radiation polarization from perpendicular to parallel with increasing number of pulses from 50 to 1000 due to variation of the dielectric constant real part of the photoexcited a-Si:H thin film from negative to positive. Such behavior of this constant is caused by concentration change for the nonequilibrium electrons excited by different number of high-power femtosecond laser pulses. According to the theoretical modelling, the excited nonequilibrium electron concentration required for turning the LIPSS direction is equal to 8.2•1021 cm–3.