ИСТИНА

Chalcogenide vitreous semiconductors (ChVS) possess high transparency in the near-infrared (IR) range, providing their applicability in infrared photonics. An important feature of these materials is possibility to form optically anisotropic controllable femtosecond laser-induced periodic surface structures (LIPSS) [1] which are of interest for polarization optics and optical data storage with multi-level coding [2, 3]. In our work we produce various LIPSS types on arsenic selenide vitreous films (As2Se3, As50Se50) and analyze their structural and optical properties. To form LIPSS on thin (850 ± 5 nm) ChVS films on chromium or quartz glass substrates, femtosecond laser pulses were used (Satsuma Amplitude Systems, 515 nm, 300 fs), with different fluence E = 34 – 270 mJ/cm2 and the number of applied pulses N = 10 – 1600. Scanning electron microscopy revealed that as a result of irradiation, various types of LIPSS with both subwavelength (~170 nm) and wavelength (~500 nm) periods are formed on the surface of ChVS films. The ridges of the structures are parallel or perpendicular to the laser polarization, respectively, and their height, according to atomic force microscopy measurements, reaches up to 100 nm. As N increases from 50 to 1600 while the value of E is constant (34 mJ/cm2), the subwavelength LIPSS transform into wavelength ones. At intermediate values of N, simultaneous formation of both structure types in the form of a hierarchical surface relief is observed. Optical transmission analysis of the of irradiated ChVS films in polarized light (633 nm) revealed optical retardance of up to 30 nm (Fig. 1), caused by the presence of one-dimensional surface relief. The possibility to control retardance in the irradiated film by varying the number of applied pulses N is shown. The difference in the refractive indices of ordinary and extraordinary waves in the IR range was up to 0.1, determined from the position of interference maxima in the IR spectra. Thus, the possibility of creating an optically anisotropic surface relief on ChVS films using femtosecond laser pulses has been demonstrated, opening perspectives of such structures as the basis for polarization-sensitive IR optics and optical memory devices. The work was supported by the Russian Science Foundation (grant 22-19-00035) https://rscf.ru/project/22-19-00035/ [1] S. Zabotnov, A. Kolchin, D. Shuleiko, et al., Periodic relief fabrication and reversible phase transitions in amorphous Ge2Sb2Te5 thin films upon mul-ti-pulse femtosecond irradiation, Micro, vol. 2, pp. 88–99 (2022) [2] K. Makino, Y. Saito, P. Fons, et al., Anisotropic lattice response induced by a linearly-polarized femtosecond optical pulse excitation in interfacial phase change memory material, Scientific Reports, vol. 6, 19758 (2016) [3] H. Wang, Y. Lei, L. Wang, et al. 100-Layer Error-Free 5D Optical Data Storage by Ultrafast Laser Nanostructuring in Glass, Laser Photonics Rev., vol 16, art. 2100563 (2022)