The Study Of Stray Light Analysis And Suppressing Technology In Large Pupil Mulit-spectal Zoom Optical System

In order to improve the detecting ability of optical detec ting system for longdistance, weak target, the entrance pupil diameter has to be larger and larger. At thesame time, the stray radiation suppression level should be increased, and then thesignal-to-noise ratio could be increased. In order to get the outline and posture of thetarget in complex environment, the multi-spectral optical system should be used, takethe advantage of the different spectral which radiated by the target to realizemulti-spectral measurement, use all of the information to improve the optical detectability, and then the multi-stray light should be suppressed. Stray radiation which isthe radiant power from other sources except target can increase the noise and decreasethe contrast of image, sometimes the signal may be inundated by the noise of strayradiation. Stray radiation affects the effective detection distance and resolving powerof the optical detecting system directly. In the infrared optical detecting system, strayradiation from thermal emission of a special environment instrument may be severalorders of magnitude larger than the irradiance of target to be observed. Therefore,when stray radiation suppression structures are designed to suppress the strayradiation coming from the outside of the infrared detecting system, their thermal strayradiation should be discussed. In this dissertation, the stray light sources andcharacteristics of the optical detecting system are analyzed. Based on the analysis, thenew mathematics model of stray light suppress structure has been built, the newsuppress structure has been put out. Then the relationship between various stray lightand optical detecting ability has been discussed. At last, a large pupil, multi-spectal,zoom optical system has been designed, the stray light suppressing level has beenanalyzed and the suppressing structure has been optimized.The main achievements and innovations are as follows:1, On the basis of classic electromagnetic theory, the scatting model of light from rough surfaces has been deduced from Maxwell equation. Furthermore, themathematics model of optical system for stray light analysis has been built, thedifferent between practical model and Lambert model has been discussed.2, Base on the traditional geometry optical theory and imaging theory, the processof the ghost has been discussed. The fast method of first-order ghost analysis inimaging system has been put forward, and the method has been confirmed by thepractical phenomenon. Then an image processing method to eliminate the ghostimage has been put forward, and it can be confirmed by the experiment.3, By the help of geometry optical theory and thermal radiation theory, the strayradiation process and characteristics of infrared optical system ha ve been analyzed.The reversal stray thermal radiation analysis method has been discussed, theadvantage and disadvantage has been compared between forward method and reversalmethod.4, The relationship between optical detecting ability and stray light suppressinglevel has been discussed. The relationship between the PST, stray light coefficient andthe star magnitude, SNR, MTF of the system has been deduced. Furthermore, therelationship between the image MTF and the PST have been proved by theexperiment.5, The new stray light suppressing structure and the calculation method for theirparameters has been put forward. A large pupil, multi-waves, zoom optical system hasbeen designed. For the design system, the method of suppressing the stray light fromout of the system, the method of decreasing ghost and narcissus and the method ofdecreasing the thermal radiant has been discussed and optimized. At last, all of thethree kinds of stray light have been analyzed, and the result shows that the system canmeet the requirement.