Development of High Power Diode Laser Systems

Development of High Power Diode Laser Systems

Development of High Power Diode Laser Systems
Von der Fakultät für Maschinenwesen der Rheinisch-Westfälischen
Technischen Hochschule Aachen zur Erlangung des akademischen Grades
eines Doktors der Ingenieurwissenschaften genehmigte Dissertation
vorgelegt von
Diplom-Physiker
Bodo Ehlers
aus Ratzeburg
Berichter:
Universitätsprofessor Dr. rer. nat. R. Poprawe M.A.
Professor Dr. rer. nat. L.H.J.F. Beckmann
Tag der mündlichen Prüfung: 20 Juni 2005
Berichte aus der Lasertechnik
Bodo Ehlers
Development of High Power Diode Laser Systems
D 82 (Diss. RWTH Aachen)
Shaker Verlag
Aachen 2005
Bibliographic information published by Die Deutsche Bibliothek
Die Deutsche Bibliothek lists this publication in the Deutsche
Nationalbibliografie; detailed bibliographic data is available in
the internet at http://dnb.ddb.de.
Zugl.: Aachen, Techn. Hochsch., Diss., 2005
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ISBN 3-8322-4572-3
ISSN 0945-084X
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Table of Contents
1 Introduction and Objective ............................................................................................ 1
2 Spatial Diode Laser Beam Transformation .................................................................... 6
2.1 Propagation of Electromagnetic Waves ................................................................... 6
2.1.1 Physical Optics................................................................................................. 6
2.1.2 The Gaussian Beam.......................................................................................... 7
2.1.3 Geometrical Optics ........................................................................................... 8
2.2 Analytical Methods for Optical Systems ................................................................. 9
2.2.1 Image Aberrations ............................................................................................ 9
2.2.2 Numerical Simulation Tools ........................................................................... 10
2.2.3 Analytical Diagnostics Tools .......................................................................... 12
2.3 Laser Light Source Models for Diode Laser Systems Modeling............................. 14
2.3.1 Diode Laser Radiation.................................................................................... 14
2.3.2 Geometrical Point Source ............................................................................... 15
2.3.3 Geometrical Extended Source......................................................................... 17
3 Rearranging of the Beams from a Diode Laser Stack................................................... 20
3.1 Basics of Beam-Parameter Rearrangement............................................................ 20
3.2 Beam Shaper Consisting of Comb Mirrors............................................................ 24
4 Spectral Diode Laser Beam Superposition ................................................................... 37
4.1 Small Footprint Design for Wavelength Multiplexing............................................ 38
4.2 Modular Design for Wavelength Multiplexing ...................................................... 48
5 Fiber Coupling of High Power Diode Laser Beams ..................................................... 55
5.1 Introduction .......................................................................................................... 55
5.2 Fiber Coupling of the 15-Bar Stack....................................................................... 57
5.2.1 Matching of the Diode Laser Beam to the Optical Fiber ................................. 57
5.2.1.1 Power and Radiance Balance ................................................................... 61
5.2.1.2 Ray Tracing Results Based on Extended Source Model............................ 64
5.2.1.3 Experimental Results ............................................................................... 65
5.2.2 Clipping of the Laser Flux Distribution .......................................................... 67
5.2.2.1 Apertures Optimization Based on Calculated and Measured Flux
Distribution.......................................................................................................... 68
6 Diode Laser Optics Creating a Variable Line-Focus .................................................... 76
6.1 Design of an Optic Producing a Two-Times Variable Line Width......................... 76
6.1.1 Design of a Gap-Bridging Beam Re-director .................................................. 78
6.1.2 Investigation of the Cylindrical Vari-Focal Lens............................................. 80
6.1.3 Performance of the Two-Times Line Width Variation Optic in Hardening
Application.............................................................................................................. 87
6.1.4 Performance Summary of the Two-Times Variable Line Width Optics........... 89
6.2 Design of a Five-Times Cylindrical Zoom............................................................. 90
7 Summary..................................................................................................................... 99
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Table of Contents
8 Symbols..................................................................................................................... 102
9 References................................................................................................................. 104
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