Performance and stability evaluation of LaF ₃ thin-film waveplates for high-power 266 nm laser applications

Glancing angle deposition (GLAD) enables the fabrication of thin film waveplates suitable for compact ultraviolet (UV) laser systems. The SiO₂ material is commonly employed due to its high laser resistance. However, all-silica waveplates exhibit instability under varying humidity because of water adsorption in the porous structure. Here, we demonstrate anisotropic LaF₃ coatings deposited using both electron beam and thermal evaporation technologies. LaF₃-based waveplates were fabricated and characterized under changing humidity conditions. LaF₃ waveplates exhibited markedly improved environmental stability, with retardance decreasing only by 0.8% in a dry environment, compared with a 5% decrease for SiO₂ waveplates. These findings position the LaF₃ material as a strong candidate for environmentally stable, low-loss UV polarizing optical coatings, particularly for components operating at 266 nm.