Simulation of external stray light in airborne off-axis four mirrors telescope system

Abstract

The off-axis four mirrors telescope has the advantages of high image quality, high resolution and high integration, which makes it a core opti-mechanical component to adapt to the future development of multiband co-aperture airborne observation and aiming systems. The simulation and suppression of external stray light in the telescope is imperative for the airborne application since this type of systems is easily affected by strong light outside the field of view. For the asymmetry of the telescope, point source transmittance (PST) as a two-dimensional function varying with the horizontal and vertical angle of stray light was set up to evaluate the influence of external stray light. Besides, the conversion relationship between the horizontal and vertical angle and the process quantity of rotations about local coordinate axis required for opto-mechanical modeling was established. Based on that, stray light simulation model of an off-axis four mirrors telescope was constructed, then PST distribution of stray lights with different spatial angles in the whole incident hemisphere space was calculated. Furthermore, the imaging effect of long-distance scene under the influence of several stray lights with large PST peak was simulated, showing that the stray lights had great interference to airborne observation. According to the found transmission paths, the internal baffles were designed to significantly reduce the peak value of PST to reach the application indices. From the re-simulation results of the imaging effect of scene, the interference of residual stray lights was finally not obvious, which could meet the use requirements of airborne photoelectric observation and aiming system.