高空高速航空相机光学窗口的热光学分析

Thermal-Optical Analysis for Optical Window of High-Altitude and High-Speed Aerial Camera

分析航空相机光学窗口的热光学特性,选定熔石英作为窗口玻璃的材料,将热流密度加权分配到窗口外表面各个区域,并考虑整个窗口玻璃的辐射来计算其在一个工作循环内的温度分布。高空高速飞行时,气动热使窗口外表面的温度急剧上升,由于熔石英的导热率很小,窗口产生很大的轴向温差,分别取轴向温差55℃,70℃和90℃时的工况计算窗口热变形;光学窗口内、外表面的变形规律为近似球面,计算了其近似曲率半径,计算由面形变化和折射率变化引起的光程差并转化为Zernike多项式;将Zernike多项式系数带入Code V中考核窗口玻璃的光学性能,得到波像差变化量,其像面离焦量为-0.114mm,调制传递函数的下降最大值小于0.01。结果表明,光学窗口满足光学性能的要求。

Thermal-optical properties of optical window in complex environment are analyzed.From the perspective of considering thermal deformation of optical window,fused silica is selected for material of the window.In order to calculate temperature distribution of optical window within a work cycle,heat flux is assigned on a scale of weight to outer surface of the window and radiation of the window is taken into account.Carrier of the window is an unmanned aerial vehicle with high-altitude and high-speed.Temperature of the window′s external surface increases sharply due to the aerodynamic heating that generated during the high-speed flight.Since thermal conductivity of fused silica is very small,a great axial temperature difference produces at the window.Heat deformation of the optical window is calculated when axial temperature difference is 55 ℃,70 ℃ and 90 ℃,respectively.Radiuses of curvature of internal and external surface of optical window are obtained approximately by rules of its deformation.Optical path difference caused by the deformation of the surface shape and refractive index changes is analyzed.Zernike polynomial coefficients are fitted.Finally,the Zernike polynomials are put into the Code V to assess the optical properties of window glass.With the introduction of wave-front aberration,change of defocus is-0.114 mm and maximum decline value of modulation transfer function（MTF） is less than 0.01.The results show that the optical window meets optical performance requirements.