Thermal optics property study and athermal design on optical window of IR aiming device reliability testing system

Optical window is used as optical interface connecting the reliability texting system for infrared aiming device with external infinite infrared simulation target which runs in acute axial temperature field, excellent thermal optics performance of optical window is the fundamental guarantee for testing system being in normal operation. In order to decrease the deformation of mirror surface caused by thermal stress, an athermal design decreasing thermal stress of optical window is put forward, a mathematical model of the deformation of optical window under axial temperature load is established and rigid body displacement after thermal deformation is analyzed by means of finite element method, the mirror surface is fitted by Zernike polynomial and introduced into optical analysis software to provide the analysis result of image quality and luminance uniformity of optical system. The rigid body displacement of optical window after athermal design decreases 0.164 mm, MTF keeps invariant basically at 20 lp/mm special frequency, the PV value and RMS value of IR optical window is just 0.342λ and 0.043λ, and uniformity of exit beam is raised up more significantly than without athermal design. The ZYGO interferometer is adopted as testing equipment detecting surface shape error (PV/RMS) of optical parallel of IR optical window. The experimental results show that the simulation results are in good agreement with the experimental results.