Research On The Thermal Deformation Mechanism Of Optical Components In A Vacuum And Low Temperature Environment

With the rapid development of the aerospace industry,various types of space optical loads and the corresponding test equipments are developed.Since space optical instruments work in a low temperature and vacuum environment,the same environmental conditions are required when testing and calibrating the space loads on the ground.Environment changes from normal temperature and pressure to low temperature and vacuum can cause thermal deformation,which affects the performance of the optical system.Therefore,opto-mechanical thermal analysis of space load and corresponding testing equipments is of great importance when design and manufacture the space optical instruments.The reflective low-temperature and vaccum collimator system with 1m aperture is selected as the typical research and analysis object.Firstly,in order to reduce the influences of gravity on the off-axis parabolic mirror and the plane mirror,we optimized the support structure and the support method with the least influences of gravity is preferred.Next,the thermal deformation of the reflective optical elements was analyzed.The Zernike polynomials are used to characterize the deformation and the influences of mirrors'thermal deformation on the system's wave aberration are analyzed.The optical transmission window is a channel connecting the external light source and the internal reflection elements in the low-temperature and vaccum collimator.The working environment of window is one side normal temperature and normal pressure,and the other side is low temperature and vacuum,so its thermo-optical characteristics are complicated.Write a user defined surface(UDS)in optical design software to characterize the thermal-induced deformation and the thermal-induced index irregularrilities simultaneously.Combining the even aspherical surface and the gradient refractive index surface in the user defined surface(UDS)to solve the problem that the complex surface shape and the complex refractive index cannot be simultaneously characterized.Then,the changing coefficients were transferred into the optical design software through the interface program to analyze the influences of window's thermal effects on the system's wave aberration.According to the relationships between the changes of system's wave aberrations and the temperature,an external zoom compensation lens group is proposed as a thermal compensation device for the collimator.The off-axis wave aberrations of the collimator system is corrected by lens tilt and decenter,and the thermal effects of the optical window is compensated by the zoom method.Through design and optimization,when the collimator system in the environment where internal vacuum 10~-33 Pa and temperature-173°C,the wave aberrations are below the diffraction limit of±40mm object field of view,and the system meets the using requirements.