Optics: measuring and testing – By particle light scattering – With photocell detection
Patent
1991-02-08
1992-07-07
Turner, Samuel A.
Optics: measuring and testing
By particle light scattering
With photocell detection
356359, 372 32, 372 29, G01B 902
Patent
active
051277310
ABSTRACT:
The phase ambiguity of conventional interferometers may be removed by using two laser diodes of different optical frequency to generate a synthetic wavelength. However, the stability requirements for a two-color interferometric laser gauge that must provide unambiguous determination of the optical fringe order over a large distance can be severe. The invention determines upper limits on the optical wavelength uncertainity and expresses same as a function of optical path difference between object and reference beams, phase measurement errors and the synthetic wavelength. A wavelength stabilization arrangement involves simultaneous servo control of two laser diodes (10, 12) with a single Fabry-Perot etalon (36). An embodiment of the invention demonstrates its effectiveness for long-term stabilized two-color interferometry over a distance of 250 mm, with a 15 .mu.m synthetic wavelength and a repeatability of 40 nm. For periods of less than 1000 seconds, the repeatability is eight nm.
REFERENCES:
patent: 4821273 (1989-02-01), Hori
patent: 4832489 (1989-05-01), Wyant et al.
patent: 4930133 (1990-05-01), Babbitt et al.
"Two-Wavelength Scanning Spot interferometer Using Single-Frequency Diode Lasers" by A. J. den Boef Applied Optics, vol. 27, No. 2, 15 Jan. 1988.
"Absolute Optical Ranging With 200-nm Resolution" by C. Williams et al. 1989 Optics Letters vol. 14, No. 11 Jun. 1989.
"Contouring Aspheric Surfaces Using Two-Wavelength Phase-Shifting Interferometry" by K. Creath et al. Optical Acta, 1985, vol. 32, No. 12, 1455-1464.
"Two-Wavelength Speckle Interferometry on Rough Surfaces Using a Mode Hopping Diode Laser" by A. Fercher, Optics and Lasers in Engineering II (1989) 271-279.
Denson-Low W. K.
Hays R. A.
Hughes Aircraft Company
Kurtz, II Richard E.
Streeter W. J.
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