Bruce C May

US Patent:

53232291, Jun 21, 1994

Filed:

Aug 31, 1992

Appl. No.:

7/938281

Inventors:

Bruce A. May - Poway CA
Thomas A. Lasko - Coronado CA
Dwight H. Everett - Encinitas CA

Assignee:

Science Applications International Corporation - San Diego CA

International Classification:

G01B 902

US Classification:

356357

Abstract:

A coherence shifting interferometry system determines the thickness or refractive index of an optically transmissive medium. The system utilizes an optical energy source for generating a source beam. The source beam is divided into two beams by reflecting one portion of the beam off of a reflective surface, e. g. , a front surface, of an optically transmissive test sample having the unknown thickness or refractive index. A second portion of the beam is transmitted through the sample and reflected off a refractive interface in the sample, e. g. , a back surface. The two reflected beams are combined into a composite beam. The composite beam is then directed to a Mach-Zehnder type interferometer, where a portion of the combined beam traverses a fixed optical path length, and another portion traverses a variable optical path length. The variable optical path length is adjusted to realign portions of the two beams and cause interference, and the amount of adjustment provides a measure of the unknown thickness or refractive index.