The optical survey instrument which is based on the spatial filtering which uses the refractive index diffraction grating

摘要

An optical inspection system ( 10 ) for comparing surface structures of test and reference objects comprises a laser ( 12 ), a photorefractive crystal ( 24 ) and a detector ( 30 ). A refractive index grating corresponding to a diffraction pattern of a surface structure of the reference object is present within the photorefractive crystal ( 24 ) and acts as a spatial filter for light diffracted by surface structures of the test objects. If a surface structure of a test object matches that of the reference object, little or no light reaches the detector ( 30 ). If the surface structure of a text object differs from that of the reference object, light of greater power reaches the detector ( 30 ). The system ( 10 ) provides a simple pass/fail comparison test and light incident on the detector ( 30 ) requires no interpretation or other processing. The system ( 10 ) may be adapted to allow simple imaging of an edge of an object.