Stray Radiation Analysis And Infrared Detection System Technology Research

In order to improve the detecting ability of dark and small target byinfrared detecting system, the stray radiation arrived at detector shouldbe decreased, and then the signal-to-noise ratio can be increased. Strayradiation is the radiant power from other sources except target. It candecrease the contrast of image and increase the noise, and sometimes thesignal may be inundated by the noise of stray radiation. Stray radiationaffects directly the detection distance and resolving power of theinfrared detecting system. In the infrared detecting system, strayradiation from thermal emission of a room-temperature instrument may beseveral orders of magnitude larger than the irradiance of target to beobserved. When stray radiation suppression structures are designed tosuppress the stray radiation coming from sources outside of the infrareddetecting system, their self thermal stray radiation should be discussedtogether. In this dissertation, the stray radiation characteristics ofinfrared detecting system are analyzed, the control methods of strayradiation are studied on the basis of the design of optical system, andhow the stray radiation suppression measures affect the detecting abilityof the system is studied.The main achievements and innovations are as follows:1, On the basis of analysis of origins of stray radiation, mathematicalmodels of stray radiation transmission in infrared detecting system areestablished according to power transmission equation between two surfaces.The key to calculate the stray radiation is defining the factor of anglesbetween surfaces.2, Stray radiations of both space-based and ground-based infrareddetecting system are analyzed. A new way to calculate stray radiation from earth and atmosphere is given by establishing a model and simulating withthe Monte-Carlo method of ray-tracing in TracePro. Stray radiations aredetailedly calculated from earth and atmosphere, sun, background and lensthermal emission. Atmospheric transmission and atmospheric radiation arealso studied.3, Infrared detecting system which type is R-C is designed. Strayradiation suppression methods are brought forward including optimizedsuppression structures and choice of surface coating. Simulations aredone to study the infrared detecting system. Point Source Transmittanceof the system and the relation between thermal radiation photon numbersand temperature are given.The validity of suppression methods is proved.4, The noise composition of the detecting system is analyzed. Theformula of signal-to-noise ratio which includes the factor of strayradiation is put forward. Several kinds of important noises arecomparatively calculated by use of equivalent photoelectron numbers. Thenoise limit of the infrared detecting system is analyzed. Thesignal-to-noise is calculated and how the thermal stray radiation affectsdetection ability is studied.