摘要
为了降低金属高反射薄膜表面微粒污染物的光学散射,分析了金属铝膜表面不同厚度的SiO_(2)保护层薄膜上半径为100 nm的球状微粒污染物球心处的电场强度,取电场强度极小值点对应的SiO_(2)薄膜的物理厚度125 nm作为SiO_(2)薄膜的优化厚度,理论计算了当波长为632.8 nm的光束正入射时,镀有优化SiO_(2)保护层的铝膜表面的双向反射分布函数(BRDF)。研究结果显示,在-90°~90°散射角内,与不镀保护层相比,优化后膜层表面污染物的散射得到了显著降低,在反射光传输方向上,镀制保护层前后B_(R)×cosθ_(s)(B_(R)为双向反射分布函数,θ_(s)为散射角)分别为0.00855和0.00048。计算了原始膜系与优化膜系表面污染物的总散射损耗,分别为0.018609和6.09264×10^(-4),优化膜系使得表面微粒的总散射降低了96.73%。最后实验镀制了四种薄膜设计,测量了相同污染条件下四种膜系表面的污染物散射情况,证实了优化SiO_(2)薄膜保护层可降低微粒污染物散射。
Objective For high-precision optical thin film devices,the scattering of optical surfaces has attracted widespread attention.When the beam enters the optical surface,the particles on the optical surface scatter the incident light and the scattered light deviates from the specular reflection direction,resulting in the loss of the effective optical signal of the system.Furthermore,when the scattered light reaches the detector surface through the optical system,it increases the stray light of the optical system,so that the influence of noise on the signal cannot be ignored and reduces the detection sensitivity of the optical system.In a high-energy laser system,even very weak light scattering influences the thermal absorption level and laser damage threshold of the film.In the reflective astronomical telescope system,the pollutants on the surface of optical elements reduce the optical performance of the devices and make the optical devices completely unusable.Presently,commonly used methods for reducing the scattering of particulate pollutants on the surface of optical elements mainly require keeping the optical surface clean and reducing pollutants on the optical surface.However,improper cleaning may fail to remove pollutants from the optical surface,damage the optical surface and increase additional light scattering.Furthermore,the material cost of pollution control for the environment where the optical elements are located is also huge.In the optical thin film evaporation process,the film particles are evaporated to the substrate surface together with the film molecules,and dot protrusions are formed on the substrate surface.This results in increasing scattering on the surface of the optical element.Here,the scattering of surface particles cannot be eliminated by cleaning and environmental maintenance.From the thin film vector scattering theory,this paper reduces the scattering amount of particulate pollutants on the optical surface by optimizing the film design,which does not require keeping the optical surface clean and can effectively reduce the frequency of optical surface cleaning to maintain the optical performance of the optical surface.Methods This study is based on the vector scattering theory.First,we theoretically calculate the electric field intensity at the center of the spherical particle on the surface of SiO_(2) film with different thicknesses on Al film surface.Second,we obtain the SiO_(2) film thickness corresponding to the minimum value of electric field intensity at the spherical particle center and set it as the optimized thickness of the SiO_(2) film protective layer.Then,the bidirectional reflection distribution function and total scattering loss of spherical particulate pollutants on the Al film surface without a protective layer and with an optimized SiO_(2) film protective layer are analyzed.Next,we compare the scattering amount of spherical particle pollutants on the surface of aluminum film without a designed protective layer and with an optimized SiO_(2) protective layer.Finally,we conduct experiments to verify the effectiveness of this method.Results and Discussions To reduce the optical scattering of particulate pollutants on the surface of metal with highly reflective films,first,we analyze the electric field intensity at the center of spherical particulate pollutants on the surface of SiO_(2) protective film with different thicknesses on the surface of the metal aluminum film(Fig.3).Next,we take the physical thickness(125 nm)of the SiO_(2) film corresponding to the minimum value of electric field intensity as the optimized thickness of SiO_(2) film.Then,we theoretically calculate the bidirectional reflection distribution function(B_(R))of the aluminum film coated with the optimized SiO_(2) protective film when the beam is normally incident(Fig.4).The results show that in the scattering angle of-90°-90°,the pollutant scattering on the surface of the optimized coating is effectively reduced,and B_(R)×cosθ_(s) in the reflected light direction without and with the optimized coating is 0.00855 and 0.00048,respectively,whereθ_(s) is the scattering angle.Furthermore,the total scattering losses of pollutants on the surfaces of the original and optimized membrane systems are calculated as 0.018609 and 6.09264×10^(-4)(Fig.5),respectively,and the total scattering of particles on the surface of the optimized membrane system is reduced by 96.73%.Finally,four coatings are prepared experimentally,and the scatterings of pollutants on the surfaces of the four coatings are measured under the same pollution conditions.The results also confirm the effectiveness of the optimized SiO_(2) film protection layer in reducing the scattering of particulate pollutants(Fig.7).Conclusions The conclusions drawn from this paper are as follows.1)The electric field intensity of particulate pollutants can be changed by changing the thickness of the SiO_(2) film protective layer on the surface of the metal Al film.Compared with that without coating on the Al film surface,the square of the normalized electric field intensity at the center of the particle is effectively reduced using the optimized thickness of the SiO_(2) film protective layer.2)Taking the square of the normalized electric field intensity at the center of the spheroidal particle pollutant as the evaluation index and the physical thickness of SiO_(2) film corresponding to the minimum value of this index as the optimized thickness of SiO_(2) film,the light scattering of the pollutant with radius of 100 nm can be reduced significantly.3)When plating a metal Al high reflector,the thickness of the SiO_(2) protective film is a physical quantity that cannot be ignored and is related to the scattering amount of the metal reflector surface.The appropriate thickness of the SiO_(2) protective film is greatly significant to reduce the surface scattering of metal mirrors,whereas improper thickness increases the surface scattering of metal mirrors.
作者
杨伟荣
潘永强
刘欢
郑志奇
李栋
周泽林
Yang Weirong;Pan Yongqiang;Liu Huan;Zheng Zhiqi;Li Dong;Zhou Zelin(School of Opto-Elect romie Engineering,Xi'an Technological Uniersity,Xi'an 710021,Shaanxi,China)
出处
《中国激光》
EI
CAS
CSCD
北大核心
2022年第18期41-46,共6页
Chinese Journal of Lasers
基金
陕西省教育厅重点实验室科研计划项目(18JS054)
陕西省自然科学基础研究计划项目(2018JM6031)。
关键词
薄膜
光学薄膜
光散射
薄膜散射
双向反射分布函数
thin films
optical films
light scattering
thin film scattering
bidirectional reflection distribution function
