Scanning interferometric methods and apparatus for measuring aspheric surfaces and wavefronts

US7612893B2 · kind B2 · utility

Assignee

• Zygo Corporation · US

Inventor

• Michael Kuchel · Oberkochen, DE

Key dates

• Filing date: Sep 14, 2007
• Grant date: Nov 3, 2009
• Expiry date: Apr 25, 2028

Classification

• Technology area (CPC G): Physics
• CPC primary: G01M11/0271
• WIPO field: Measurement
• WIPO sector: Instruments

Abstract

Interferometric scanning method(s) and apparatus for measuring test optics having aspherical surfaces including those with large departures from spherical. A reference wavefront is generated from a known origin along a scanning axis. A test optic is aligned on the scanning axis and selectively moved along it relative to the known origin so that the reference wavefront intersects the test optic at the apex of the aspherical surface and at one or more radial positions where the reference wavefront and the aspheric surface intersect at points of common tangency (“zones”) to generate interferograms containing phase information about the differences in optical path length between the center of the test optic and the one or more radial positions. The interferograms are imaged onto a detector to provide an electronic signal carrying the phase information. The axial distance, ν, by which the test optic is moved with respect to the origin is interferometrically measured, and the detector pixel height corresponding to where the reference wavefront and test surface slopes match for each scan position is determined. The angles, α, of the actual normal to the surface of points Q at each “zone” …