Optics: measuring and testing – By polarized light examination – With light attenuation
Patent
1992-02-12
1993-08-24
Rosenberger, Richard A.
Optics: measuring and testing
By polarized light examination
With light attenuation
356371, 250561, 385 78, G01B 1124, G01N 2186
Patent
active
052393666
ABSTRACT:
Optical metrology apparatus, specifically a laser probe (1), includes a frame (10) comprised of a material selected to have a predetermined coefficient of thermal expansion. A beamsplitter (36) is coupled to the frame for generating a sample beam optical path (D) and a reference beam optical path (C). The beamsplitter is optically coupled to an optical fiber (12) that delivers radiation to and conveys radiation from the frame. A piezoelectric stack (48) has an excitation signal coupled thereto and includes a mirror (26) for phase modulating the reference beam optical path length in response to the excitation signal. The laser probe includes a first strain gauge (58) that is coupled to the piezoelectric stack and a second strain gauge (60) that is coupled to the frame. A closed loop control system (A1, A2, A3, A4, VR) varies the excitation signal in accordance with the detected strains so as to maintain the reference beam optical path length in a predetermined relationship to a path length of the sample beam optical path. This athermalizes the probe, in that any expansion or contraction of the frame is matched by the piezoelectric stack, yielding a net zero change in the non-common beam path lengths. The apparatus includes an optical fiber support (14) that is rotatably coupled to the frame for positioning the optical fiber at a desired angular position.
REFERENCES:
patent: 4758065 (1988-07-01), Dorman et al.
patent: 4796994 (1989-01-01), Bager
patent: 5042949 (1991-08-01), Greenberg et al.
patent: 5153669 (1992-10-01), DeGroot
DeGroot Peter J.
Hayes Guy H.
Kittell David H.
Denson-Low Wanda K.
Huges Aircraft Company
Pham Hoa Q.
Rosenberger Richard A.
Sales Michael W.
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