A computer modelling approach to decrease stray light in low light non imaging optical designs

Selcuk Seyhun; Huseyin Sari

doi:10.1117/12.2014364

Abstract

Opto-mechanical structures (objectives) are employed to transfer photons which are collected from their field of view (FOV) to the detector plane. The sensors used in such systems have high gain which causes them to detect stray light originated from the mechanical body of the objective. This type of stray light is a major problem in low light nonimaging optical systems used in laser seekers which employ four quadrant position sensors to determine laser illumination reflected from a target surface positioned kilometers away. This work, mainly concentrates on reducing unwanted stray light caused by inner mechanical structure of large FOV objectives with the use of software tools. Stray light in an optical system can not be totally eliminated. However, it can often be reduced to a level at which it is tolerable. This works focuses on reducing unwanted stray light originating from mechanical structure of the objective in a cost efficient way. In order to prevent this unwanted stray light a sample laser seeker objective is designed in ZEMAX software environment together with its mechanical mount. Black delrin is used as the objective material. Its specular and diffused reflective properties are measured with spectrophotometer and defined in the software environment. Ten objectives with different baffle height/pitch ratio (h/p) are designed and used in the same optic design. In order to show that a software model can be used to find the optimum h/p ratio for eliminating stray light, prototype objectives are manufactured and tested with readout electronics. After making measurements with different angles on incidence values best applicable objective with a certain baffle h/p ratio is found. It is verified that the h/p ratio found in software model is in very good agreement with the measurement results. This helps us not use more baffles than necessary since increasing baffle h/p astronomically increases production and workmanship costs. This study shows that, instead of manufacturing expensive prototypes computer simulation can be used to identify and also take necessary precautions to prevent or decrease stray light before production. This prevents loss of significant amount of time, work, and cost.

Citation Download Citation

Selcuk Seyhun, Selcuk Seyhun, Huseyin Sari, Huseyin Sari, "A computer modelling approach to decrease stray light in low light non imaging optical designs", Proc. SPIE 8550, Optical Systems Design 2012, 85500C (18 December 2012); doi: 10.1117/12.2014364; https://doi.org/10.1117/12.2014364

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