Experimental Studies into the Beam Parameter Product of GaAs High-Power Diode Lasers

P. Crump1, M. Elattar1, Md.J. Miah1, M. Ekterai1, M.M. Karow1, D. Martin1, A. Maaßdorf1, S. McDougall2, C. Holly2, S. Rauch2, S. Gruetzner2, S. Strohmaier2, and G. Tränkle1

Published in:

IEEE J. Sel. Top. Quantum Electron., vol. 28, no.1, pp. 1501111 (2022).

Copyright © 2021 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See https://www.ieee.org/publications/rights/index.html for more information.

Abstract:

Experimental studies into the beam parameter product (BPP) of 940–980 nm GaAs-based high-power diode lasers are presented. Such lasers exhibit broadening far field and narrowing near field with increasing bias, with BPP increasing tenfold over the diffraction limit. First, spectrally-resolved beam profile measurements of lasers with monolithically-integrated gratings are presented, showing that a reproducible series of spatially-extended optical modes makes up the optical field. Then, changes to the device construction are presented, enabling effects limiting BPP to be inferred and addressed. Process- and package-induced effects can be minimized by design, while the effects of carrier, gain and temperature profiles dominate. Self-heating within the laser stripe raises the refractive index, forming a thermal lens, and the variation in curvature of this lens with bias and device construction directly affects BPP. Temperature non-uniformity along the resonator is also shown to strongly degrade BPP. Moreover, current spreading and the resulting lateral carrier accumulation (LCA) amplify high-order, high-BPP modes, thus degrading BPP for any given thermal lens. This LCA-induced degradation is shown to be suppressed by regrown lateral current-blocking structures. Finally, a flatter thermal lens and lower BPP can be achieved using thermal engineering, via changes to the epitaxial design or device layout.

1 Ferdinand-Braun-Institut gGmbH, Leibniz Institut für Höchstfrequenztechnik (FBH), 12489 Berlin, Germany
2 TRUMPF Laser GmbH

Index Terms:

Distributed feedback devices, Quantum well lasers, Far field, Near field, Semiconductor device thermal factors, High-power lasers, Energy conversion, Multimode waveguides.