1064 nm激光高反膜残余应力及其形变分析

Residual Stress and Deformation of 1064 nm High Reflection Films for Laser Systems

目的由于光学薄膜自身的残余应力,致使镀膜前后基底面型变化较大。针对这一问题,本文制备单层膜和激光高反膜,明确单层膜应力机制,以此研究不同膜系高反膜的应力情况及其面型变化,通过增加压应力补偿层减小面型变化,为制备微变型激光高反镜提供方法。方法从理论上分析单层膜残余应力机制,采用等效参考温度的方法代替光学薄膜本征应力的效果,通过仿真方法得到薄膜的本征应力。使用有限元分析和试验方法研究激光高反膜的残余应力情况。以单层膜试验为依据,使用等效参考温度、生死单元和载荷步技术,仿真分析多层膜–基系统的残余应力分布及其面型变化。采用电子束热蒸发技术制备不同的高反膜,通过Zygo激光干涉仪测试其镀膜前后的面型,分析基底初始面型、膜料和膜系对高反镜面型的影响。结果仿真发现,多层膜–基系统残余应力呈现层状分布,从基底到膜层由拉应力变为压应力,再由压应力变为拉应力。在残余应力作用下,整个多层膜–基系统呈凹形,位移呈环状分布。对于TiO_(2)/SiO_(2)组合,通过分析对比不同膜系下对应每一层膜层的残余应力及其对整体面型的影响,发现膜系G│(HL)^(10)H2L│A比G│(HL)^(10)H│A面型的变化更小。试验发现,通过增加压应力补偿层使得高反膜的残余应力减小,高反镜(熔石英基底,ϕ30 mm×2 mm)的面型基本没有变化(ΔPV=0.004λ),这与仿真结果一致。结论熔石英基底上TiO_(2)、HfO_(2)、H4和SiO_(2)的本征应力在残余应力中起主导作用,TiO_(2)、HfO_(2)和H4一般表现为拉应力,SiO_(2)表现为压应力。不同膜料组合的高反膜体系均表现为压应力。膜系G│(HL)^(10)H2L│A比G│(HL)^(10)H│A残余应力和面型变化更小,其残余应力为-39.70 MPa,比不加补偿层减小了22.26 MPa,面型基本没有变化。当加2L应力补偿层时,在满足光谱特性的基础上可以平衡多层膜整体残余应力。

The large surface shape change on the substrate after coating is due to the residual stress of the optical films.It presents a challenge for coating optical elements with high precision surface shape.The work aims to study the residual stress mechanism and surface profile shape change of monolayer films and laser high reflection films with different films on substrate.The surface shape change of the substrate is reduced by adding a compressive stress compensation layer on the outermost layer of the multilayer films.It provides a method for preparing micro-deformation laser high reflection mirrors.The residual stress mechanism of monolayer film is analyzed by the theory of thermal stress and residual stress in optical films.The equivalent reference temperature is used to replace the intrinsic stress of optical thin films,and the intrinsic stress of optical thin films is obtained by simulation.The residual stress distribution and surface shape change of laser high reflection films-substrate system is studied by finite element analysis and experiments.Based on the stress of monolayer film,the residual stress distribution and surface profile change of high reflection films-substrate system is simulated and analyzed by equivalent reference temperature,birth and death element and load step technology.Different high reflection films are prepared by thermal evaporation of electron beam.The effects of initial substrate surface profile,films material and films combinations on high reflection films-substrate system are analyzed via testing surface profile changes of it,using Zygo laser interferometer.The simulation results show that the residual stress of high reflection films-substrate system is layered.It changes from tensile stress to compressive stress and then to tensile stress in the direction from the substrate to films.The surface profile of high reflective films-substrate system is concave and the Z-axis displacement is distributed annularly due to residual stress.By analyzing the influence of monolayer film on the substrate surface shape and comparing the residual stress value of each film layer in different high reflective films systems,it is found that the surface profile change of G│(HL)^(10)H2L│A is smaller than G│(HL)^(10)H│A with TiO_(2)/SiO_(2).The surface profile of substrate with high reflective films(fused silica substrate,ϕ30×2 mm)is basically unchanged(ΔPV=0.004λ)because the residual stress of films reduced by adding a compressive stress compensation layer,which is consistent with the simulation results.On the fused silica substrate,the intrinsic stress of TiO_(2),HfO_(2),H4 and SiO_(2)plays a leading role in the residual stress.The residual stress of TiO_(2),HfO_(2),H4 is tensile on the fused silica substrate while the SiO_(2)is compressive.All the high reflection films systems with different material combinations show compressive.For TiO_(2)/SiO_(2),the films-substrate system G│(HL)^(10)H2L│A is smaller than G│(HL)^(10)H│A in residual stress of optical films and the change of surface shape on substrate.Its residual stress value is–39.70 MPa,which is 22.26 MPa less than that without stress compensation layer.Its surface shape has basically not changed.The addition of 2L(stress compensation layer)balances the residual stress of the multilayer films-substrate system without affecting the spectral characteristics.