Optics: measuring and testing – By particle light scattering – With photocell detection
Patent
1992-05-06
1994-12-06
Warden, Robert J.
Optics: measuring and testing
By particle light scattering
With photocell detection
356357, 356358, G01B 902, G01B 1102
Patent
active
053715870
ABSTRACT:
An interferometer with a dual laser source having a tunable frequency separation between the laser emissions is used to measure absolute distance to weakly-reflecting targets. A dual-laser source is commonly characterized by a synthetic wavelength, which is equal to the speed of light divided by the frequency separation with time over a total frequency range that is small compared to the average frequency separation. Simultaneously, a high-speed phase modulator generates a signal whose amplitude is proportional to the interferometric fringe visibility, and data acquisition means are used to record the fringe visibility as a function of time during the synthetic wavelength chirp. Signal processing means are then used to extract the frequency and phase of the resultant quasi-periodic fringe-visibility curve. The optical path is then determined to high accuracy without the phase ambiguity problems of prior-art synthetic-wavelength techniques. An optical fiber implementation of a preferred embodiment of the invention operates over a 0.1 to 10 inch range, using a 0.01-inch diameter 100 .mu.W laser beam, with an absolute error of less than 0.001 inch (25 .mu.m). The invention can be used for dimensional gauging, surface profiling and position measurement, and will improve productivity and quality control in manufacturing.
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de Groot Peter J.
McGarvey John A.
Carpenter Robert
The Boeing Company
Warden Robert J.
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