The Influence Of Temperature On The Stress And Optical Properties Of Near Infrared Optical Thin Films

With the development of thin film technology,the application of optical thin films is more and more extensive.Optical thin films are applied to many aspects,such as daily life,precision instruments and aerospace equipments.The application of infrared optical thin films is facing complex environmental changes,and the performance change is obviously influenced by temperature.The changes in the mechanical and optical properties of the optical thin film will cause the change of the properties of the film.Therefore,this paper mainly studies the effect of temperature on the stress and optical properties of the optical thin film.The optical thin films are mainly obtained by the physical vapor deposition method under the condition of high temperature and non-equilibrium in vacuum,so the performance of thin films is affected by stress.This paper first introduces the basic classification of stress,and focuses on the thermal stress caused by thermal mismatch between film and substrate.The horizontal strain and the bending strain formula of thermal strain are obtained,and the thermal stress calculation formulas are derived by the traditional bridge bending theory and the displacement coordination condition.The thermal stress distribution can be calculated more quickly and effectively by the approximate solution,when the thickness of the film is much smaller than the substrate.It is found that thermal stress has nothing with the other films by the approximate solution.In practical applications,the thermal stress distribution of infrared narrow band-pass filters is calculated.The common infrared films of SiO2 and Si were deposited by electron beam evaporation.The effects of temperature variation on the stress and optical properties of the films were studied.It is found that the stress values of SiO2 and Si increase with the increase of thickness from 0.5?m to 2?m.At the same time,as the temperature increases and the temperature is less than or equal to the deposition temperature,the stress of the film decreases continuously.The results are compared with the calculated values of the thermal stress,and the stress in the temperature range is dominated by the thermal stress.In addition the influence of temperature on the optical properties of SiO2 and Si films is analysed,which has little effect on the spectral properties.The transmittance of SiO2 film shows long wavelength shift with the increase of temperature,and the Si film moves towards short wavelength.At the same time,the refractive index of the film is changed with the temperature variation.The influence of temperature change on the optical properties of metal film is studied,and the Ag film of wide spectral reflector in space remote sensing is discussed the influence of temperature change on its polarization characteristics.A silver thin film mirror was been designed and fabricated.The polarization change of the mirror was been measured and discussed when temperature changes from 25? to 150? at 45°and 60°incidence angles.When the temperature was increased,the phase difference ? between reflected s and p polarized light decreased in the range of 350~600nm wavelength,keep stable in 600~650nm wavelength,and increased in 650~1200nm wavelength.The surface scattering and absorption of Ag thin film appeared when temperature reaches 125?.In the end,references is given for the practical application of Ag mirror.