Interferometric probe for distance measurement utilizing a diffraction reflecting element as a reference surface

Abstract

An interferometric probe for measuring the distance to the surface of an object has a light source, for example, a super-luminescent diode, that produces a coherent light beam preferably such as to produce a speckle pattern in light reflected from the object. An interferometer includes a beam splitter that produces a reference beam directed towards a reference diffracting reflector and a measuring beam directed towards the surface of the object to be measured. The diffracting reflector produces a plurality of diffraction orders each of which are combined with portions of the light reflected from the surface to produce interference, which is detected by a detector system having a number of individual detectors equal to the number of diffracted orders of the reference beam that are used. Use of the diffracting reflector enables more of the light reflected from the object to be used in the detector and improves signal-to-noise ratio. A further enhancement of signal-to-noise ratio can be produced by the addition of a second detector system that uses the reflected part of the combined beam from the beam splitter and is used differentially to improve the signal-to-noise ratio.

Dependencies are inferred from the claim text.