Radiant energy – Photocells; circuits and apparatus – Photocell controls its own optical systems
Patent
1996-07-31
1998-09-01
Allen, Stephone B.
Radiant energy
Photocells; circuits and apparatus
Photocell controls its own optical systems
356400, G01N 2186
Patent
active
058013890
ABSTRACT:
In a position detecting apparatus, a light beam from a white light source is guided through a collimator lens etc. to be converted into a parallel beam, and this parallel beam is incident to a first acousto-optic modulator (AOM) and a second acousto-optic modulator positioned with a spacing by which a phase difference between diffracted light is approximately m.sup..pi. (where m is an integer). Traveling waves of slightly different frequencies opposite to each other are supplied in opposite directions to the two acousto-optic modulators, and the position detecting apparatus executes position detection by the heterodyne interference method as guiding a beam comprised of +first-order diffracted light from the acousto-optic modulators and a beam comprised of -first-order diffracted light from the acousto-optic modulators through an objective lens to project them with a predetermined intersecting angle onto a diffraction grating mark.
REFERENCES:
patent: 5070250 (1991-12-01), Komatsu et al.
patent: 5329354 (1994-07-01), Yamamoto et al.
patent: 5347356 (1994-09-01), Ota et al.
patent: 5488230 (1996-01-01), Mizutani et al.
Mizutani Hidoe
Ota Kazuya
Allen Stephone B.
Nikon Corporation
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