Research On Stray Light Of Optical And Mechanical System Based On BRDF

A good stray light suppression is essential to well behaved optical systems. In the past stray light analysis, as the missing of scatter data, diffuse reflection model or mirror reflection model is used for building the optical-mechanical surface scatter. This is not true under practical application, which leads to an inaccurate result to the stray light analysis, so that the stray light design cannot achieve desired results.In order to increase the accuracy of stray light analysis, bidirectional reflection distribution function (BRDF) of contaminated optical surface is modeled with theoretic method, and the BRDF of mechanical surface is measured and modeled. The result shows that the scatter of alufer surface distributes mainly in10°around the mirror reflection direction. Take R-C optical system for example, optical-mechanical model is built in TracePro software. Then in-field and out-of-field stray light analysis is done, and the result is evaluated by veiling glare index and point source transmittance (PST). In-field stray light analysis is done based on mirror scatter, particulate contamination and mirror diffraction. The result shows that the primary mirror has the highest contribution to diffraction stray light irradiance while the fold mirror has the highest contribution to the scatter stray light. In addition, to get an in-field veiling glare index under1%, the RMS roughness of mirrors should be proposed under5nm, and the cleanness level (CL) should be controlled under500. Out-of-field stray light analysis is done which mainly aims at stray light restrain designs. The result of analysis shows that, there is a rather big difference between the PST obtained based on diffuse reflection model and the measured BRDF model, which indicates that analysis based on the measured BRDF model can get more accurate results. What`s more, baffle vans design based on measured BRDF data get the best stray light suppression result.At last, some stray light restrain treatments are proposed based on the main stray light paths, and stray light analysis is taken on the disposed optical-mechanical system. The analysis shows that, the veiling glare index reduce by1%and the PST is102lower, which proves the efficiency of the treatments.