Thin film metallic glass broad-spectrum mirror coatings for space telescope applications

Abstract

The use of metallic glasses as coatings on silicon carbide substrates for applications as optical mirrors was investigated. Various alloy compositions were chosen, limited by the available method of synthesis by electric arc melting, using the rule of mixtures to predict their reflectance. After a preliminary experimental study on bulk specimens, two alloys were selected for production as thin film metallic glasses by physical vapour deposition on silicon carbide substrates. The alloy Zr44Cu40Al8Ag8 (at.%) was sputtered from a single target. In a separate co-sputtering experiment, two targets, one of Al90Ni5Y5 (at.%), the other of pure Zr, were deposited. The structure, roughness, and reflectance of the films were investigated. The measured reflection was compared with the predicted values for wavelengths between 250 nm and 2000 nm. The reflectance of the Al-based mirrors was uniform around 70% across the UV/Vis/near-IR spectrum range significantly improving that of the polished silicon carbide substrate.

Keywords

• Optical mirrors
• Metallic glass
• Sputtering
• UV/Vis/near-IR
• PVD
• Reflectance