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.
