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14 October 2004 Image grid errors due to the application of a local heat source on the TIR surface of a prism
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Abstract
The sensitivity of an image position grid to local heat applied to the TIR surface of a prism in a Wynne Dyson design was examined. The mechanisms resulting in the shape and magnitude of the shape change are explored qualitatively and with FEA analysis. The FEA package was used to generate temperature and deformation results, which were then ported to a ray trace program and the impact on the image grid was determined. A device was made to check the validity of the models. The heat load was applied by inserting thermocouple instrumented Watlow cartridge heaters in an aluminum block, placing the aluminum block 127 microns from the TIR surface, and heating an 8mm square surface area of the block to 1.3C, 2.5C and 5.0C. These heat loads resulted in peak image errors of 68nm/C with vector error maps in an annular pattern roughly centered on the geometrical center of the heat load. The models developed were useful for qualitative predictions of the performance, but need tuning to increase the accuracy. Although linear superposition cannot be used to calculate the effect of combined local heat sources, due to the non-linear behavior of the thermal effects, the results can be used to estimate the maximum stray local heat that can be tolerated on this optical surface.
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Roger C. Sumner and Shiyu Zhang "Image grid errors due to the application of a local heat source on the TIR surface of a prism", Proc. SPIE 5523, Current Developments in Lens Design and Optical Engineering V, (14 October 2004); https://doi.org/10.1117/12.560206
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