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Stochastic tandem microlens arrays for beam homogenization

: Wippermann, F.C.; Radtke, D.; Dannberg, P.; Zeitner, U.D.; Bräuer, A.


Forbes, A. ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
Laser Beam Shaping IX : 11.8.2008, San Diego, California, USA
Bellingham, WA: SPIE, 2008 (SPIE Proceedings Series 7062)
ISBN: 978-0-8194-7282-3
ISSN: 0277-786X
Paper 70620Q
Conference "Laser Beam Shaping" <9, 2008, San Diego/Calif.>
Fraunhofer IOF ()
laser beam shaping; optical system design; coherent optical effect; fourier optic; microlens array

Fly's eye condensers are commonly used for the beam shaping of an arbitrary input intensity distribution into a top hat. The setup usually consists of a Fourier lens and two identical regular microlens arrays - often referred to as tandem lens array - where the second one is placed in the focal plane of the first microlenses. As a consequence of the periodic structure of the regular arrays, the output intensity distribution is modulated by equidistantly located sharp intensity peaks. We propose a new concept for fly's eye condensers incorporating a stochastic tandem microlens array for the generation of an intensity far field distribution with improved homogenization under coherent illumination with the envelope of a top hat. The influences of the variance of the lens parameters and the number of illuminated lenses on the homogenization results are discussed. Measurements obtained at first prototypes fabricated by laser lithography and a subsequent UV-replication are presented.