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Homogeneous intensity within the Rayleigh length and enhanced depth of focus for Gaussian beams

: Bischoff, Christian; Jäger, Erwin; Umhofer, Udo; Lasagni, Andrés-Fabián; Völklein, Friedemann

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Journal of Laser Micro/Nanoengineering. Online journal 15 (2020), No.3, pp.178-185
ISSN: 1880-0688
Bundesministerium für Bildung und Forschung BMBF (Deutschland)
Eurostars; 01QE1852A
OpEn Laser Lathe
Journal Article, Electronic Publication
Fraunhofer IWS ()
beam shaping; optical simulation; diffractive optic; phase shifting element; laser processing

The smallest width of a Gaussian beam at the focal plane is called waist and is only limited by the diffraction limit of the light. The waist determines the Rayleigh length which is the distance from the waist at which the width of the Gaussian beam increases by a factor of 21/2 or the intensity decreases by a factor of 2. With regard to laser material processing, these changes in spot size and intensity are typically undesirable. For example, variations in surface profiles or thickness of the processed material could require adjustment of focus. In this simulation study, we present a beam shaping method based on a development of the Fundamental Beam Mode Shaper (FBS) concept for enhanced depth of focus. Using this concept, an enhancement of Rayleigh length of 20% and a more homogeneous peak intensity around the focal plane is achieved.