Simulation and evaluation of stray radiation from optical window effects on infrared detection system

Stray radiation analysis is a special radiation transport problem characterizing the directional propagation and small probability simulation. The computational cost increases significantly when lens or optical windows exist in the optical system, due to the simulation requirement for ray transmission in the semi-transparent medium. For the high-temperature optical window outside of the hypersonic vehicle etc., the infrared radiation from window becomes the main stray radiation and reduces the detection or image quality adversely. To fulfil the infrared stray radiation analysis for such optical system and improve the efficiency, an equivalent model of infrared emission for the optical window is presented. According to the simulation of ray generation and propagation in the optical window, the equivalent model is built combining the distributions of launch point and direction for the infrared stray radiation. Then, a simplified infrared optical detection system is taken to verify the presented equivalent model. The infrared stray radiation flux and direction distribution are recorded on the entrance pupil plane of the optical system using Monte Carlo method. The results show that the infrared stray radiation analysis method, employing the equivalent model of infrared emission, is reliable and more effective.