1 December 1997 Improved collimation testing technique using a digital moire method
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Optical Engineering, 36(12), (1997). doi:10.1117/1.601562
An optical arrangement using a wedge-plate shearing interferometer and a digital image processing system are devised for laser beam collimation. A modification of Xu and Rosenbruch’s method is presented that involves the rotation of a large-angle wedge plate by 180 deg and taking the absolute value of the result of the digital subtraction between the two shearing interferometric fringe patterns. The use of digital moire´ fringes for collimation testing is analyzed and the principle is verified experimentally. The defocusing errors in obtaining the perfect collimation by this method are calculated. It is found that the rotating wedgeplate method for obtaining digital moire´ fringes in collimation testing is twice as sensitive as the plane-parallel-plate method and also this method is a self-referencing collimation testing method, i.e., it does not require a horizontal reference mark and calibration of the position of the wedge direction. The laser beam divergence can be calculated directly by measuring the digital moire´ fringe spacing in this optodigital arrangement.
Hong Zhang, Michael J. Lalor, David R. Burton, "Improved collimation testing technique using a digital moire method," Optical Engineering 36(12), (1 December 1997). http://dx.doi.org/10.1117/1.601562


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