1982-06-29
1984-06-26
Punter, William H.
350407, G02F 101
Patent
active
044563396
ABSTRACT:
Method and apparatus for testing the deviation of the face of an object from a flat smooth surface using a laser beam having two plane-polarized components, one of a frequency greater than the other to produce a difference frequency with a phase to be used as a reference. The beam also is split into its two components which are directed onto spaced apart points on the face of the object. The object is rotated on an axis coincident with one component as a reference. The other component follows a circular track on the face of the object as the object is rotated. The two components are recombined after reflection to produce a difference frequency having a phase that is shifted in an amount that is proportional to the difference in path length as compared to the reference phase to produce an electrical output signal proportional to the deviation of the height of the surface along the circular track. The output signal is generated by means of a phase detector that includes a first photodetector in the path of the recombined components and a second photodetector in the path of the reference phase. The output signal is dependent on the phase difference of the two photodetector signals. A polarizer, a quarter-wave plate and a half-wave plate are in series in the path of the reference phase. Rotation of the half-wave plate can be used for phase adjustment over a full 360.degree. range for initial calibration of the apparatus.
REFERENCES:
patent: 3620593 (1971-11-01), Tackaberry
patent: 3796495 (1974-03-01), Laub
patent: 4105338 (1978-08-01), Kuroha
Delfino, G., "Two-Beam Method for Measurements of the Kerr Constant with Fixed Polarizers," Optics Comm. 9-1971, pp. 60-62.
Redner, S., "New Automatic Polariscope System," Exp. Mech. (U.S.A.), 12-1974, pp. 486-491.
Paillette, M., "Kerr Effect: Application to Phase & Electric Field Induced Absorption Measurements in Glasses", Optics Comm. 3-1982, pp. 140-144.
Matsuura et al., "Measurement of Optical Phase Difference Using a Polarization Technique", Optics & Laser Tech., 12-1977, pp. 285-289.
Fuernges, D., "Optical Dual-Beam Measurements of Small Phase Swings of Modulated Light Waves", Nachrich Tentechnische Zeitschrift NTZ, 7-1976, pp. 544-546.
Clouse, Jr. Clifton E.
Esposito Michael F.
Gaither Roger S.
Punter William H.
The United States of America as represented by the United States
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