The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Sep. 20, 1994
Filed:
Aug. 07, 1992
Peter DeGroot, Bellevue, WA (US);
Hughes Aircraft Company, Los Angeles, CA (US);
Abstract
Metrology method and apparatus (10) for determining a characteristic of an object's surface. The apparatus includes a multiple wavelength source (12) having an optical output. The source is comprised of a multimode laser diode (18) for simultaneously providing a plurality of wavelengths from which a synthetic wavelength is derived for metrology purposes. The apparatus further includes a beamsplitter (30), preferably a polarizing beam splitter, coupled to the optical output for providing a reference beam (32) and a measurement beam (34), the measurement beam impinging on the surface and the reference beam being phase modulated. The apparatus also includes optical elements and devices for detecting a phase difference between the reference beam and a reflected measurement beam for determining the characteristic of the surface. A diffraction grating (60) is blazed for a nominal characteristic output of the laser diode, such as 785 nanometers, and spatially resolves the various wavelengths of the returned laser light. The resolved wavelengths are provided as two beams by a lens system (62) and are detected by a pair of photodetectors (64, 66). A data processor ( 68) coupled to an output of the photodetectors determines an interferometric phase at the two wavelengths and the surface characteristic.