Impact of longitudinal refractive index change on the near-field width of high-power broad-area diode lasers

S. Rauch1, H. Wenzel2, M. Radziunas3, M. Haas1, G. Tränkle2 and H. Zimer4

Published in:

Appl. Phys. Lett., vol. 110, no. 26, pp. 263504 (2017).

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Typical for broad-area laser (BAL) diodes operating in a continuous-wave mode is a narrowing of the near-field (NF) width at the output facet for high injection currents (output powers). This phenomenon increases the facet load of BALs, resulting in a reduction in the level of catastrophic optical mirror damage. In this letter, we demonstrate theoretically that thermally induced changes in the refractive index in both lateral and longitudinal directions not only cause the NF narrowing at the front facet but also a broadening of the NF at the back facet. In contrast, a sole lateral self-heating induced variation in the refractive index (commonly referred to as thermal lensing) does not result in a NF narrowing. Our theoretical findings are confirmed by measurements of the current-dependent profiles of the NF at the back and front facets of a BAL with a stripe width of 120 µm emitting at 960 nm. Furthermore, our quasi three-dimensional thermo-electro-optic simulations indicate that a longitudinally homogeneous device temperature can reduce the front-facet load while keeping the beam quality unchanged compared with the experimental results.

1 TRUMPF Laser GmbH, Aichhalder Straße 39, 78713 Schramberg, Germany
2 Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik, Gustav-Kirchhoff-Str. 4, 12489 Berlin, Germany
3 Weierstrass Institute for Applied Analysis and Stochastics, Mohrenstrasse 39, 10117 Berlin, Germany
4 TRUMPF Photonics, 2601 US Route 130 S, Cranbury, New Jersey 08512, USA