DIFFRACTIVE ELEMENT IN OPTICAL INSPECTION OF PAPER

A computer-generated diffractive optical element to produce 4 x 4 spot matrix images was fabricated by electron-beam lithography. The elemen t was applied to the inspection of paper sheets. Images of spot matric es were analyzed, and agreement between the reflectance measured by th e present sensor and a spectrophotometer was observed. The sensor imag e was able to yield information about local curvature as well as defec ts. Moreover, sensor images from surfaces of different paper samples r evealed material surface anisotropy in the cross-correlation analysis of image data. (C) 1998 Society of Photo-Optical Instrumentation Engin eers. [S0091-3286(98)03805-7].