Patent ID: 6064482
Filing Date: 2000-05-16
Classification: G01B

Abstract:
An interferometric measuring device for measuring a rough surface profile on a test object, comprising:a radiation-generating unit providing an input radiation which is coherent over a short distance;a parallel-shifting arrangement including a reflecting element which has a retro grating, the parallel-shifting arrangement periodically changing a path of a light;an evaluation device;a beam-splitter device producing a reference beam and a measuring beam, the reference beam being directed at the parallel-shifting arrangement, the measuring beam being directed at the test object, the beam-splitter device including a beam splitter element, a heterodyne element and a photodetector,wherein the beam-splitter device provides an interference between the reference beam from the test object and the reference beam from the parallel-shifting arrangement, the parallel-shifting arrangement being situated at least in a path of first rays of the reference beam, andwherein the reference beam is diffracted before passing through the parallel-shifting arrangement and after passing through the parallel-shifting arrangement, the photodetector detecting a radiation of the interference and transmitting the radiation to the evaluation device;a modulation-interferometer arrangement generating the reference beam and a further beam component using the beam-splitter device;a first compensation grating situated in the path of the first rays upstream from the parallel-shifting arrangement;a second compensation grating situated in a path of second rays of the further beam component;a further retro grating situated in the path of the second rays downstream from the second compensation grating, the second compensation grating and the further retro grating being identical to the first compensation grating and the retro grating, respectively, wherein a first path difference between a first path optical path length of the reference beam and a second path optical path length of the further beam component is greater than a predetermined coherence length, wherein the first compensation grating feeds back the reference beam, and the second compensation grating feeds back the further beam component, and wherein the reference beam and the further beam component are joined to form an intermediate beam; anda demodulation-interferometer arrangement splitting the intermediate beam into a first arm and a second arm using the heterodyne element, the first arm terminating in a reflector, the second arm terminating in a surface of the test object, wherein the first path difference is equal to a second path difference between a path of the first arm and a path of the second arm, and wherein the reflector and the surface of the test object redirect beams to interfere at the heterodyne element.