Analysis of bulk and facet failures in AlGaAs-based high-power diode lasers Jens W. Tomm* a , Martin Hempel a , Fabio La Mattina b , Frank M. Kießling c , Thomas Elsaesser a a Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie, Max-Born-Str. 2A, 12489 Berlin, Germany; b EMPA, Swiss Federal Laboratories for Materials Science and Technology, Überlandstraße 129, 8600 Dübendorf, Switzerland; c Leibniz-Institut für Kristallzüchtung, Max-Born-Straße 2, 12489 Berlin, Germany ABSTRACT Mechanisms are addressed limiting the reliability high-power diode lasers. An overview is given on the kinetics of the Catastrophic Optical Damage (COD) process, which is related to highest output powers. It involves fast defect growth fed by re-absorption of laser light. Local temperatures reach the order of the melting temperature of the waveguide of the device. The process starts either at a facet or at any weak point, e.g., at extended defects in the interior of the cavity. Keywords: High-power diode lasers, degradation mechanisms, catastrophic optical damage 1. INTRODUCTION High-power diode lasers are the root-source of photonic energy in most laser systems. Conversion efficiencies exceeding seventy percent make them the most efficient man-made device for converting electric into photonic energy. This importance is motivation for research on how to exploit the entire potential of these lasers. There are principal physical limits: This involves basic properties of the semiconductor materials such as the intraband (momentum) relaxation time and band offsets (barrier heights) [1] setting intrinsic limitations. Extrinsic limits are mainly given by thermal effects resulting among others in deterioration of beam properties reducing the brightness of the devices at highest powers. Moreover, irreversible processes such as degradation become relevant and will be addressed in the following. Although the history of diode lasers is obviously a story of success, it was always accompanied by device failures. If one reliability problem has been solved, another part of the diode laser became the bottleneck limiting the overall performance on an improved reliability level. The problem of facet degradation has probably been ‘solved’ several times (and this has been claimed in the literature as well), but the achievement of further increased power levels, again made the facet a problem. The related defect mechanism became called Catastrophic Optical Damage (COD). Meanwhile this effect is not limited to the outcoupling facet, where it has been first discovered in the early days of diode lasers. If the outcoupling facet is well protected, it might appear at rear facets [2, 3] or within the bulk [4-6]. Thus COD is rather a potentially limiting mechanism stringently related to high power levels than being only an indication of ‘facet problems’. COD is a sudden degradation process of edge-emitting diode lasers. In involves fast defect growth at local temperatures on the order of the melting temperature of the waveguide of the device. Such temperatures are achieved by localized re- absorption of laser light. The process starts either at a facet or at a weak point, e.g., at an extended defect in the interior of the cavity. It results in a specific defect pattern within the quantum well (QW) plane. COD is not only producing high temperatures, it is also thermally activated. The thermal activation mechanisms are independent from the time scale considered and hold across 15 orders of magnitude on the time scales from nanoseconds to years [7-9]. As mentioned, COD results in specific defect pattern within the QW plane. The appearance of this pattern is absolutely independent on the starting point of COD, facet or bulk. Therefore we do not distinguish between ‘Catastrophic Optical Mirror Damage’ (COMD) and ‘Catastrophic Optical Bulk Damage’ (COBD) but use here the common denotation COD. The use of another term than COD seems important in those cases, when, e.g., the bulk damage effect is of different microscopic nature (and produces different types of defect pattern); see e.g. [10]. *tomm@mbi-berlin.de; phone +49-(0)30-63921453; fax 1+49-(0)30-63921459; mbi-berlin.de Invited Paper Novel In-Plane Semiconductor Lasers XII, edited by Alexey A. Belyanin, Peter M. Smowton, Proc. of SPIE Vol. 8640, 86401F · © 2013 SPIE · CCC code: 0277-786X/13/$18 · doi: 10.1117/12.2003465 Proc. of SPIE Vol. 8640 86401F-1 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 03/14/2013 Terms of Use: http://spiedl.org/terms EMPA20130484