Performance of a zoom homogenizer for reshaping coherent laser beams

We have reshaped the TEM00 beam emitted by a diode-pumped Nd-Yag laser by means of an optical homogenizer with zoom. The laser beam, first enlarged up to a size of (100 x 37.5) mm(2), is homogenized and resized to a final dimension continuously adjustable from (130 x 4.5) mm(2) Up to (130 x 52) mm(2). We measured the plateau uniformity, the root mean square fluctuation and the edge steepness of the beam according to the ISO standard definitions, showing a poor reliability of the above parameter values due to the definitions themselves, and propose an amendment to overcome this problem. We obtained a very sharp edge steepness, but the spatial coherence of the laser beam put a lower limit to the high-frequency intensity fluctuations on the plateau region of the homogenized beam. Finally, we discuss the optimum homogenizer design for spatially coherent laser beams, including the depth of focus issue. (c) 2006 Elsevier B.V. All rights reserved.