The Research Of Low-loss Absorption In Oxide Optical Coatings

The absorption of optical films seriously affects the beam quality,transmission efficiency,and laser damage threshold of the optical system.At present,optical films made by oxide materials are used in large laser systems to achieve their optical functions.As laser energy continues to increase,lower and lower absorption of the oxide optical film is needed.The absorption of an optical film can be caused by interacting of photons with electrons,excitons,lattice vibrations,impurities,and defects in the film.At present,the preparation of optical films involves an ultra-quenching process from gaseous phase to solid phase.A large amount of impurities and defects are present in the film,and these are sources of absorption in the transparent band of the optical film.In this paper,the main reasons affecting the absorption are discussed by analyzing the optical characteristics of the films prepared by different methods.The mechanism of absorption loss of optical films is studied from the aspects of impurities and defects in films.The main work includes:?1?The absorption from ultraviolet to 1064nm of impurities in quartz glass was investigated,and the linear relationship between the amount of hydroxyl in quartz glass and the extinction coefficient at 1064 nm was calculated.The influences of the atomic arrangement disorder on the ultraviolet absorption were measured in quartz crystal and quartz glass,and the Urbach energy of quartz glass was calculated.The results show that the absorption of 1064 nm of quartz glass is independent of the oxygen vacancy defect and is proportional to the hydroxyl content.?2?The water content,hydroxyl content and short-wave absorption spectra of SiO₂ films prepared by electron beam evaporation,ion assisted and magnetron sputtering were studied.The band gap width,Urbach energy and ODC?I?content of the films were calculated by analyzing the short-wave absorption,thus the micro-defect informations?stoichiometric ratio,atomic arrangement,and point defect?in the films were obtained.The effects of annealing in air on the microscopic defects of SiO₂ films were investigated.The photoluminescence and corresponding defects of three SiO₂ films were measured and analyzed.The effects of Urbach energy,water content and hydroxyl content on 1064 nm absorption of electron beam evaporation SiO₂ film were discussed.It was proved that the oxygen vacancy in the film were not related to 1064 nm absorption.?3?The absorption spectrum of the EBD Ta₂O₅ film showed the absorption was not caused by the Urbach band tail,but related to the color center in the film.When the Ta₂O₅ film prepared by IAD method,the bandgap width was increased and the non-stoichiometric ratio was reduced.The infrared spectrum showed that the Ta=O bond can reduce the short-wave absorption of the film.The photoluminescence spectra of the films were tested,in combination with absorption spectra the microscopic defects and absorption mechanisms of the films were analyzed.The relationship between the energy of assisted ion and optical properties of Ta₂O₅ film was studied.A multi-wavelength high performance filter for high resolution solar tomography was designed and prepared.?4?The HfO₂ films prepared by EBD and IAD methods have low absorption.Short-wave absorption is reduced and the band gap width is increased after annealing in air.After reannealing in argon,the absorption is increased and the band gap width is decreased.The results show that the ultraviolet band absorption of the film is caused by oxygen vacancy defects,and the shorter wavelength has a larger absorption.Corresponding to the photoluminescence,crystal orientation and absorption of HfO₂film,the mechanism of the emission spectrum was analyzed.It is proved that the five luminescence peaks are not related to oxygen vacancy defects,and the absorption mechanism of HfO₂ film is preliminarily explained.The process parameters of HfO₂film such as assisted ion energy and substrate temperature were optimized for low absorption at 1064 nm.