Optical thin films with high reflectance, low thickness and low stress for the spectral range from vacuum UV to near IR

Abstract

This paper presents approaches to achieve high reflective metal mirrors from 1064 nm—the near infrared (NIR)—down to 150 nm—the vacuum ultraviolet (VUV) spectral region. Metal (aluminium or silver) sublayers with dielectric (oxide and fluoride) protected and enhanced optical coatings are sought as solutions for high reflectance with low thickness and stress. Aluminium and silver with oxide enhanced optical coatings can provide reflectance above 99% for wavelengths at 248, 308, 633 and 1064 nm, with total thickness varying from 400 to 950 nm. As for the VUV spectral region, high reflectance around 90% has been realized based on an aluminium layer with fluoride capping layers. Single fluoride and oxide materials have achieved reflectance above 90% at 193 nm. Due to the short total thickness and specially optimized deposition process, these highly reflecting coatings possess stresses lower than ± 60 MPa, which is very promising for stress-sensitive substrates, such as micro-structured mirrors.