Formation of laser-induced periodic surface structures on an As$_{50}$Se$_{50}$ film under femtosecond laser irradiation with wavelengths of 400–800 nm
Abstract:
Laser-induced periodic surface structures (LIPSS) on chalcogenide glassy semiconductors are of great interest in relation with creating polarization-sensitive optical elements. This study investigates the formation of LIPSS on the surface of As$_{50}$Se$_{50}$ amorphous film, fabricated by thermal vacuum deposition, under femtosecond laser irradiation in the wavelength range from 400 to 800 nm. The periods of various LIPSS types depend linearly on the laser wavelength. The measured birefringence of so-called low spatial frequency LIPSS, formed by different irradiation wavelengths, are in the 10–85 nm range. The maximum birefringence of 85 nm was obtained for structures irradiated at a 480 nm wavelength. A significant decrease in birefringence was observed at a wavelength of 800 nm, which may be due to the formation of a less pronounced and more disordered surface relief caused by less effective absorption of modifying laser radiation with photon energy lower than optical band gap of As$_{50}$Se$_{50}$. Decreased optical absorption observed in As$_{50}$Se$_{50}$ films with LIPSS is caused by increased light scattering on the surface relief.
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