Optics: measuring and testing – By particle light scattering – With photocell detection
Patent
1986-03-18
1987-12-01
McGraw, Vincent P.
Optics: measuring and testing
By particle light scattering
With photocell detection
356356, 356363, 356400, G01B 902
Patent
active
047100265
ABSTRACT:
An apparatus includes a means for providing a predetermined frequency difference between two light beams and generating an optical beat with respect to interference between first and second diffracted light beams from a diffraction grating formed on a substrate, and a means for detecting a phase difference between the optical beat and a reference signal having a frequency corresponding to the frequency difference between the two light beams, and detects a position of the substrate based upon the phase difference in accordance with an optical heterodyne interference method.
REFERENCES:
patent: 4636077 (1987-01-01), Nomura et al.
Ichihara Yutaka
Magome Nobutaka
McGraw Vincent P.
Nippon Kogaku K. K.
Turner S. A.
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