Novel Interferometer

摘要

Thin, visibly opaque components for use in infrared transmission present a challenge in tolerancing and manufacture: Most optical shops do not have access to infrared interferometry and so must evaluate the opposing surfaces in visible light. The inevitable bending of thin parts creates surface deformations that are individually far in excess of allowable limits. However, if the opposing surface deformations track each other, the part may be perfectly functional. The dilemma lies between over-specification of the surfaces and consequent multiplication in costs and schedule vs. verification in the infrared, thus eliminating most perfectly competent vendors. Herein, I present a novel interferometric cavity setup using a standard, commercial interferometer, in which the test beam reflects twice from each side, in point-by-point registration across the aperture. I also present fringe-scaling factors based on angle of incidence and index of refraction. The cavity error can be conveniently subtracted. Small wedge can be measured or eliminated, or if desired, large wedge can be eliminated. The components can, thus, be specified and verified functionally with significant reduction in difficulty. NOTE―this work was presented at SPIE in 1991, v 1527 p 188. The audience that day was very small. I think the technique remains valuable and virtually unknown.