Interferometric methods and apparatus for measuring distance to

Details Interferometric methods and apparatus for measuring distance to Interferometric methods and apparatus for measuring distance to

1975-03-14

1977-02-01

Hubler, Malcolm F.

Optics: measuring and testing

Range or remote distance finding

With photodetection

356106R, G01C 308

Patent

active

040059367

ABSTRACT:
For measuring surface motion or profile, laser beams of two different frequencies .omega..sub.1 and .omega..sub.2 (from one laser or two) are each split into two parts. Frequency shifts of .delta..omega..sub.1 and .delta..omega..sub.2 are introduced into one part of the respective beams. One part of each beam (preferably the parts which are not frequency-shifted) are directed on to, and reflected from, the surface of interest. These reflected parts of the beams, together with the non-reflected parts, are received at either a single or two separate photosensitive detectors so that the parts of similar frequency interfere coherently with one another. From the detector(s) is derived a difference frequency (.delta..omega..sub.1 -.delta..omega..sub.2) whose phase is a measure of the distance to the surface. The effect is equivalent to allowing the phase-change to be measured at a wavelength which is comparable with the relevant changes in the distance, instead of at a very much smaller wavelength, thereby inter alia reducing ambiguities.

REFERENCES:
patent: 3360987 (1968-01-01), Flower et al.
patent: 3409369 (1968-11-01), Bickel
patent: 3463924 (1969-08-01), Culshaw et al.
patent: 3503682 (1970-03-01), Botcherby
patent: 3522992 (1970-08-01), Jaffe
Kroeger et al., AF Technical Documentary Report No. AL TDR 64-233, Clearinghouse AD 606643, Mar. 1965, 356-365.

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