Method for testing an optical window with a small wedge angle

Details Method for testing an optical window with a small wedge angle Method for testing an optical window with a small wedge angle

1993-10-04

1995-03-14

Turner, Samuel A.

Optics: measuring and testing

By dispersed light spectroscopy

Utilizing a spectrometer

356345, 356353, G01B 902

Patent

active

053981120

ABSTRACT:
The invention provides a technique for eliminating "ripple" or ghost fringes from a wavefront transmitted by an optical window with a very small wedge angle, distortions in the wavefront being measured by an interferometer. A collimated beam produced by the interferometer is transmitted through the optical window, which is tilted so as to prevent direct reflections from entering a detector of the interferometer. The beam transmitted through the window is reflected by a return flat back through the window and transmitted to the detector. The return flat is tilted slightly in the direction of or opposite to the direction of tilt of the window, causing the re-incident angle of the returned ray to be different from the original incident angle of the collimated beam. This causes the multiple reflections within the window to be different and to be out of phase. The ghost fringes are cancelled by appropriately tilting the return flat.

REFERENCES:
patent: 4818108 (1989-04-01), Eppinger
patent: 5335059 (1994-08-01), Maruyana et al.
"Digital wave front measuring interferometer for testing optical surfaces and lenses" by J. H. Bruning, D. E. Gallagher, D. P. Rosenfeld, A. D. White, D. J. Brangaccio, and D. R. Herriott, Appl. Opt. 13, pp. 2693-2703 (1974).
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"Evaluation of Fizeau interferences by phase-shifting interferometry" by R. A. Nicolaus, Optik 87, pp. 23-26 (1991).
"Effect of retroreflection of a Fizeau Phase-shifting interferometer" by C. Ai and J. C. Wyant, Appl. Opt., in press.

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