High-accuracy high-stability method and apparatus for measuring

Details High-accuracy high-stability method and apparatus for measuring High-accuracy high-stability method and apparatus for measuring

1999-01-08

2000-09-26

Pham, Hoa Q.

Optics: measuring and testing

By polarized light examination

With light attenuation

25655931, 25655938, G01B 1100

Patent

active

061249343

ABSTRACT:
A system for measuring the distance of an examined surface from a reference plane includes two detectors and a radiation source for directing a beam along a path which includes a first focussing lens for focussing the beam as a spot on the surface and reflecting it. A collecting lens converts the reflected radiation to a reflected beam. A splitter directs part of the reflected beam through a second path which includes a second focussing lens for focussing part of the reflected beam onto a surface of the first detector. Its position on the first detector corresponds to the distance of the examined surface under the spot from the reference plane, according to by a first equation with two terms: a first drawback error and a first surface displacement. The other part of the reflected beam propagates through a splitter and along a third path which includes a third focussing lens for focussing the other part of the reflected beam onto a second spot on a surface of the second detector. Its position on the second detector corresponds to the distance of the examined surface from the reference plane according to a second equation with two terms: a second drawback error and a second surface displacement. The second and third focussing lenses cause the first and second equations to be independent. A processing unit utilizes the outputs of the detectors to measure the distance of the examined surface from the reference plane.

REFERENCES:
patent: Re35350 (1996-10-01), Shahar et al.
patent: 5298976 (1994-03-01), Shahar et al.
patent: 5311288 (1994-05-01), Shahar

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