Interface Roughness Control Of Optical Thin Films And Anti-scattering Properties

Optical scattering loss is one of the main scattering losses of optical thin films.Reducing surface roughness is not a effective way to solve scattering because of its high cost and theory.So,some new method must be developed to reduce it with the development modern optical technology.In this paper,the surface roughness and anti-scattering properties of optical thin films are studied.First,by analyzing BRDF model of single layer optical thin film,requirement of anti-scattering is found.Then,single layer TiO₂ and SiO₂ thin films were deposited by electron beam thermal evaporation and influence of process parameters on the surface roughness of the films was investigated.The last,characteristics of the scattering reduction were verified by comparing the BRDF values before and after the coating.The concrete conclusions are as follows:?1?Based on the scattering model of single surface,the scattering model of single layer optical thin film is derived.According to the simulation of the model,the rule of BRDF on the surface of the thin film is found,and the anti-scattering of the single layer thin film are deduced.The conditions of the anti-scattering of the single film are given,including different refractive index,film thickness,the ratio range of surface roughness of the substrate and surface roughness of the film.?2?When the roughness of the substrate is different,the surface roughness of the TiO₂ film increases with the increase of the roughness of the substrate.With the increase of the deposition rate,the surface roughness of the films decreases and then tends to be gentle;using ion assisted deposition can reduce the surface roughness of the film,but the ion source energy size changes little effect;with the increase of film thickness,surface roughness of the films decreases first and then increases.?3?When the roughness of the substrate is different,the surface roughness of the SiO₂ film increases with the increase of the surface roughness of the substrate.Using ion source assisted deposition will reduce the surface roughness of the film,but the change of the energy of the ion source has little effect.With the increase of the thickness of the film,the surface roughness of the film will continue to increase.?4?Comparing the BRDF of the surface roughness of the substrate and BRDF of the surface roughness caused by different TiO₂ thin films what is found:When the ratio is within a certain range,whether or not greater than or smaller than the ratio of the best scattering reduction,BRDF always decreased.Meanwhile,the closer to the zero scattering value in theory,the smaller the BRDF is.Comparing the BRDF of the surface roughness of the substrate and BRDF of the surface roughness caused by different SiO₂ thin films what is found:When the ratio is within a certain range,BRDF always decreased.Meanwhile,the closer to the zero scattering value in theory,the smaller the BRDF is.