Distance measurement by laser light

Details Distance measurement by laser light Distance measurement by laser light

1985-04-10

1988-05-17

Paschall, M. H.

Optics: measuring and testing

Range or remote distance finding

With photodetection

356448, 356 45, G01C 308

Patent

active

047446536

ABSTRACT:
Method and apparatus for measuring a distance to an object includes directing first and second laser beams having frequencies .omega..sub.11 and .omega..sub.12 toward the object. A first reference signal is derived having a beat frequency .omega..sub.1 =.omega..sub.11 -.omega..sub.12. A first reflected light beam reflected from the object is detected and has the beat frequency .omega..sub.1 and a first phase difference with respect to the first reference signal. The first phase difference is then extracted from the first reference signal and the first reflected light beam and a first plurality of distance nodes is calculated from the first phase difference. Then, the frequency of the second laser beam is changed to .omega..sub.13. A second reference signal having a beat frequency of .omega..sub.2 =.omega..sub.11 -.omega..sub.13 is then derived. A second reflected light beam reflected from the target is detected and has the beat frequency of .omega..sub.2 and a second phase different with respect to the second reference signal. The second phase difference is then extracted from the second reference signal and the second reflected light beam and a second plurality of distance nodes is then calculated from the second phase difference. Finally, the minimum distance node coincident between the first and second pluralities of nodes is selected as the distance to the object.

REFERENCES:
patent: 3970389 (1976-07-01), Mendrin et al.
patent: 4037933 (1977-07-01), Yano et al.
patent: 4600299 (1980-07-01), Abshire
Optical Engineering Journal of the Society of Photo-Optical Instrumentation Engineers, H. J. Caulfield/Editor, Elaine C. Cherry/Managing Editor, Jan./Feb. 1981, vol. 20, No. 1, ISSN 0036-1860, pp. 126-134.
Mode Competition in Lasers with Homogeneous Line Broadening, W. J. Witteman, IEEE Journal of Quantum Electronics, vol. QE-5, No. 2, Feb. 1969, pp. 92-97.

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