Multilayer antireflection optical coatings based on Nb, Si and Al oxides for nonlinear ZnGeP2 crystals

The effect of the designed antireflection coatings based on Nb₂O₅/Al₂O₃ and Nb₂O₅/SiO₂ pairs of materials on the laserinduced damage threshold (LIDT) of ZnGeP₂ crystals at a wavelength of 2097 nm is shown. The coating was applied using the ion-beam sputtering (IBS) method. The LIDT of the sample coated with Nb₂O₅/SiO₂ was W_0d = 1.8 J/cm². The LIDT of a sample coated with Nb₂O₅/Al₂O₃ is W_0d = 2.35 J/cm². The presence of silicon conglomerates in the antireflection coating leads to a decrease the LIDT of a nonlinear crystal due to local thermomechanical stresses and scattering of the incident laser radiation.