High resolution alignment interferometer

An optical apparatus for detecting very small angular misalignment of a reflective surface with respect to a reference plane, said apparatus comprising a beam splitter-reflector having a light-receiving entrance face, an exit face, from which light is transmitted and a base parallel to said reference plane and spaced in facing relation to the reflective surface, said beam splitter-reflector further having a beam splitting interface, a collimated light source directed to said interface, said beam splitter-reflector having means for producing a zero order interference fringe fixed at an apex of said beam splitter-reflector and lying along a reference line and which rotates about an axis at said apex in response to misalignment of said reflective surface from said reference plane, and means for responding to the position of said zero order fringe whereby misalignment of said reflective surface from said reference plane may be detected.

An interferometer comprising a beam splitter-reflector having first and second planes and a beam-splitting plane disposed intermediate thereto, said first and second planes being arranged to reflect parallel rays in response to a light source aimed at said first plane toward said beam-splitting interface, a reflective surface disposed substantially normal to said beam-splitting interface, one of said planes being rotated about a line extending therethrough and normal to an apex defined by the intersection of said first and second planes, whereby a zero order fringe interference is provided fixed at the apex of said beam splitter-reflector and rotating about an axis at said apex as of function of angular displacement of said reflective surface with respect to the plane normal to said beam-splitting plane, and means for measuring the position of a zero order fringe viewed at said second plane whereby angular misalignment of said reflecting surface with respect to the plane normal to said interface is determined.