Method and apparatus for measuring near-angle scattering of mirror coatings

US8502987B1 · kind B1 · utility

Assignee

• The United States of America as represented by the Administrator of the National Aeronautics and Space Administration · US

Inventors

• Russell A. Chipman · Tucson, US
• Brian J. Daugherty · Ann Arbor, US
• Stephen McClain · Eindhoven, NL
• Steven A. Macenka · Altadena, US

Key dates

• Filing date: Feb 1, 2011
• Grant date: Aug 6, 2013
• Expiry date: Mar 24, 2032

Classification

• Technology area (CPC G): Physics
• CPC primary: G01N2021/4735
• WIPO field: Measurement
• WIPO sector: Instruments

Abstract

Disclosed herein is a method of determining the near angle scattering of a sample reflective surface comprising the steps of: a) splitting a beam of light having a coherence length of greater than or equal to about 2 meters into a sample beam and a reference beam; b) frequency shifting both the sample beam and the reference beam to produce a fixed beat frequency between the sample beam and the reference beam; c) directing the sample beam through a focusing lens and onto the sample reflective surface, d) reflecting the sample beam from the sample reflective surface through a detection restriction disposed on a movable stage; e) recombining the sample beam with the reference beam to form a recombined beam, followed by f) directing the recombined beam to a detector and performing heterodyne analysis on the recombined beam to measure the near-angle scattering of the sample reflective surface, wherein the position of the detection restriction relative to the sample beam is varied to occlude at least a portion of the sample beam to measure the near-angle scattering of the sample reflective surface. An apparatus according to the above method is also disclosed.