A frequency-scanning interferometer is modified to include a diffuse reference surface. An illuminating system produces an expanding measuring beam, portions of which reflect from a test object surface and the diffuse reference surface on converging paths to an imaging system. Interference patterns between...http://www.google.de/patents/US7057742?utm_source=gb-gplus-sharePatent US7057742 - Frequency-scanning interferometer with non-specular reference surface
