The present invention relates to an apparatus and method for measuring physical properties of an object, such as thickness, group index of refraction, and distance to a surface. The apparatus includes a non-coherent light interferometer (53) and a coherent light interferometer (55) in association so...http://www.google.com/patents/US5659392?utm_source=gb-gplus-sharePatent US5659392 - Associated dual interferometric measurement apparatus for determining a physical property of an object
