Study On The Influence Of Deposition Angle On The Performance Of Optical Coatings

With the continuous maturity of precision optical system preparation technology,the technical requirements for the design,manufacture and integration of optical systems have increased dramatically.As an important part of optical film technology,high-performance optical films must be prepared to meet the ultra-high demands of precision optical systems.However,the deposition angle of the film at different locations in the vacuum coating of concave or convex optical elements in optical systems varies,resulting in changes in the optical properties and microstructure of the optical films on them,which hinders the realization of high performance optical films on the surfaces of concave or convex optical elements.In this paper,we designed a fixture for simultaneous preparation of tilt angles of0°,10°,20°,30°,40°,50°,and 60°to exclude other interference factors other than the film deposition angle in the film preparation process.The single layer hafnium oxide（Hf O₂）and silicon oxide（Si O₂）thin films under different deposition angles were prepared by electron beam evaporation equipment.The optical properties such as refractive index,scattering and absorption loss were examined in detail.It was found that the influence of deposition angle on the properties of Hf O₂ and Si O₂ thin film was mainly reflected in cross-sectional structure,film thickness,spectral properties,refractive index and scattering.The above single layer film data is brought into the design of multilayer high reflection film and antireflection film with a central wavelength of 365 nm under ideal conditions,and the influence of deposition angle on the spectral performance of the multilayer antireflection film and high reflection film is simulated and analyzed.Thermal annealing,as a common post-processing method for thin films,can effectively change the microstructure and optical properties of optical thin films.High temperature tube furnace annealing was used to anneal Hf O₂ and Si O₂ films at different deposition angles at 200～400℃.The effects of annealing on the microstructure and optical properties of Hf O₂ and Si O₂ films at different deposition angles were systematically studied.Experiments show that thermal annealing can reduce the optical loss of Hf O₂ film due to the increase of deposition angle and the dispersion of Si O₂ film under different deposition angles without increasing the surface roughness of the film.The surface roughness of magnesium fluoride（Mg F₂）and lanthanum fluoride（La F₃）thin films prepared by electron beam evaporation increases with the increase of deposition angle.In view of the change of interface roughness caused by deposition angle,antireflection coating with a narrow range of angle of incidence,antireflection coating with a wide range of angle of incidence,and multilayer high reflection coating at 193 nm are designed respectively in this paper.The maximum deviations of the s and p polarized light transmittances of the antireflection coating are 0.17%and 0.44%,respectively.Combining the scalar scattering theory and the theory of effective absorption layer,the rough interface between the multilayer film is equivalent to a thin absorption layer.It is shown that the spectral performance of the thin film degrades sharply with the increase of the root mean square roughness of the interface,and the reflection bandwidth of the high reflection film also decreases.The existence of interface roughness is an important factor affecting the preparation of vacuum ultraviolet optical thin films with hyperspectral properties.