2026
Applied Surface Science, Q1
Article
Nonlinear crystals for optical parametric conversion typically exhibit strong Fresnel reflection from the endfaces mediated by high material refractive index limiting optical coupling efficiency and device performance. Anti-reflective nanostructures engraved on the crystal endfaces offer promising alternative to gradient-index coatings lacking adhesion, thermal and mechanical stability, while enhanced transmittance at short-wave IR (SWIR) wavelengths requires high-resolution nanotexturing techniques. Here, based on the example of promising multi-component BaGa4Se7 crystals exhibiting broad transparency (0.5 – 17 mkm) and high nonlinear coefficient, we demonstrated applicability of direct femtosecond laser nanotexturing via self-organization to create anti-reflective nanostructures. In particular, we utilized visible (515 nm) and UV (257 nm) laser pulses to drive transient interference of incident light with surface and scattered waves imprinting nanogratings with wavelength-dependent morphology and subwavelength periodicity Λ = λ/1.3. Such nanogratings referred to as laser-induced periodic surface structures (LIPSS) produced over both crystal endfaces were found to provide 1.22-fold enhancement of the SWIR transmittance as evidenced from FTIR spectroscopy and power measurements of spectrally tunable laser radiation directly passing the crystal bulk. Our study sheds light on the LIPSS formation over nonlinear crystal surfaces highlighting laser-driven self-organization as a promising high-resolution nanofabrication technique for improving pump efficiency of nonlinear crystals.
https://doi.org/10.1016/j.apsusc.2026.166873