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Proceedings Paper

Low-loss smile-insensitive external frequency-stabilization of high power diode lasers enabled by vertical designs with extremely low divergence angle and high efficiency
Author(s): Paul Crump; Steffen Knigge; Andre Maaßdorf; Frank Bugge; Stefan Hengesbach; Ulrich Witte; Hans-Dieter Hoffmann; Bernd Köhler; Ralf Hubrich; Heiko Kissel; Jens Biesenbach; Götz Erbert; Guenther Traenkle
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Paper Abstract

Broad area lasers with narrow spectra are required for many pumping applications and for wavelength beam combination. Although monolithically stabilized lasers show high performance, some applications can only be addressed with external frequency stabilization, for example when very narrow spectra are required. When conventional diode lasers with vertical far field angle, ΘV 95% ~ 45° (95% power) are stabilized using volume holographic gratings (VHGs), optical losses are introduced, limiting both efficiency and reliable output power, with the presence of any bar smile compounding the challenge. Diode lasers with designs optimized for extremely low vertical divergence (ELOD lasers) directly address these challenges. The vertical far field angle in conventional laser designs is limited by the waveguiding of the active region itself. In ELOD designs, quantum barriers are used that have low refractive index, enabling the influence of the active region to be suppressed, leading to narrow far field operation from thin vertical structures, for minimal electrical resistance and maximum power conversion efficiency. We review the design process, and show that 975 nm diode lasers with 90 μm stripes that use ELOD designs operate with ΘV 95% = 26° and reach 58% power conversion efficiency at a CW output power of 10 W. We demonstrate directly that VHG stabilized ELOD lasers have significantly lower loss and larger operation windows than conventional lasers in the collimated feedback regimes, even in the presence of significant (≥ 1 μm) bar smile. We also discuss the potential influence of ELOD designs on reliable output power and options for further performance improvement.

Paper Details

Date Published: 26 February 2013
PDF: 13 pages
Proc. SPIE 8605, High-Power Diode Laser Technology and Applications XI, 86050T (26 February 2013); doi: 10.1117/12.2000528
Show Author Affiliations
Paul Crump, Ferdinand-Braun-Institut (Germany)
Steffen Knigge, Ferdinand-Braun-Institut (Germany)
Andre Maaßdorf, Ferdinand-Braun-Institut (Germany)
Frank Bugge, Ferdinand-Braun-Institut (Germany)
Stefan Hengesbach, RWTH Aachen Univ. (Germany)
Ulrich Witte, Fraunhofer-Institut für Lasertechnik (Germany)
Hans-Dieter Hoffmann, Fraunhofer-Institut für Lasertechnik (Germany)
Bernd Köhler, DILAS Diodenlaser GmbH (Germany)
Ralf Hubrich, DILAS Diodenlaser GmbH (Germany)
Heiko Kissel, DILAS Diodenlaser GmbH (Germany)
Jens Biesenbach, DILAS Diodenlaser GmbH (Germany)
Götz Erbert, Ferdinand-Braun-Institut (Germany)
Guenther Traenkle, Ferdinand-Braun-Institut (Germany)

Published in SPIE Proceedings Vol. 8605:
High-Power Diode Laser Technology and Applications XI
Mark S. Zediker, Editor(s)

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