Method of alignment with the use of diffraction gratings and an apparatus therefor
US5000573A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Mar 12, 1990 |
| Grant date | Mar 19, 1991 |
| Priority date | — |
| Expiry date | Mar 12, 2010 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG03F9/7049
- WIPO fieldOptics
- WIPO sectorInstruments
Abstract
In a method of measuring/adjusting a relative displacement of objects using diffraction gratings, two monochromatic beams each having slightly different frequencies are synthesized to cause optical heterodyne interference so as to generate two beat signals. One of the beat signals is used as a reference signal. The other is used as a first interference beat signal generated by emitting the two monochromatic beams on a first diffraction grating arranged on a first object and by synthesizing two diffracted beams generated from the first diffraction grating by the above emission to cause optical heterodyne interference. A phase difference between the reference beat signal and the interference beat signal is then detected. Finally, the relative displacement is measured/adjusted in accordance with the phase difference.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.