Antireflective coating on TeO2 crystal for the high power acousto-optic modulator

Abstract

The purpose of this research is to develop broadband antireflection (A/R) coating for a high power acousto-optic modulator with the following specifications: the substrate material is TeO2 and the requirement of T (transmittance) for both sides greater than 98% in the spectral region 410–700 nm with laser power damage threshold is greater than 40 W/mm2. The technology of A/R coating is based on the conventional method of nonreactive evaporation from electron beam gun sources oxides of Zr (ZrO2 films as a layer with high refractive index) and Si (SiO2 films as a layer with low refractive index), and YF3 (yttrium fluoride) films on TeO2 crystals substrate with pre-cleaning by using an ion beam gun (Refs. Reference 1 and Reference 5). The refractive indices of the mentioned films are: n(ZrO2)=1.96–1.98, n(SiO2)=1.45–1.46, and n(YF3)=1.48–1.50 (Ref. Reference 2). In all cases properties of A/R coating are strongly dependent on the method of surface cleaning, type of polishing, and even the bulk properties of the substrate.