|
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.
|
