Thermal robustness of ion beam sputtered TiO2/SiO2, TiO2/Al2O3 and Al2O3/SiO2 IR anti-reflective coatings on YAG and sapphire substrates

As optical coatings are deployed in more extreme environments and applications, mechanical and environmental robustness must be taken into account when designing the film(s). Even minor degradation of the film structure from these outside factors can affect final fluence handling capabilities in operation, and limit the life of the coating. We present the results of a study of maximum thermal handling capabilities of Broad-Band IR Anti-Reflective coatings in the mid-IR (3 to 5 micron) regime. We prepared a family of coated optics utilizing different coating material sets on different substrate materials, and exposed them to a range of increasing temperatures. We examined the damage morphologies under dark field, bright field, and Nomarski microscopy.