Thermal and mechanical issues of high-power laser diode degradation
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Research Letter
Thermal and mechanical issues of high-power laser diode degradation Jorge Souto, José Luis Pura, and Juan Jiménez, GdS Optronlab, Ed.LUCIA, Paseo de Belén 19, Universidad de Valladolid, 47011 Valladolid, Spain Address all correspondence to Jorge Souto at [email protected] (Received 1 June 2018; accepted 26 June 2018)
Abstract A computational model for the evaluation of the thermomechanical effects that give rise to the catastrophic optical damage of laser diodes has been devised. The model traces the progressive deterioration of the device running in continuous wave conditions. The local heating of the active layer locally leads to the onset of the plastic regime. As a result, dislocations and threads of dislocations grow across the active layers and lead to rapidly growing temperatures in the quantum well. The poor power dissipation under these conditions has been identified as the key factor driving the final degradation of the laser.
Introduction High-power laser diodes under continuous wave (cw) operation are devices with extremely elevated internal power densities within their active regions. A very high percentage of that power is effectively converted into light, but over 25% is transformed into heat. Therefore, heat dissipation is a crucial point in the fabrication of reliable semiconductor lasers. Three main degradation processes have been identified for laser diodes: rapid, gradual, and catastrophic failure modes.[1] Rapid degradation is characterized by a sharp drop of the optical power output in a time scale of hours, during the initial operation of the device. This malfunction can be easily screened by burn-in tests. Gradual degradation is a slow process that involves an ongoing decrease of the laser output power when used in cw, and which eventually determines the lifetime of a device with normal operation life. Catastrophic failure, the mode on which we will focus in this work, is a sudden and almost instantaneous degradation of the device that can occur after a certain period of normal operation of the device. This failure mode is usually known as catastrophic optical damage (COD); it can take place either at the facet mirror or at interior zones of the laser cavity, and is associated with the generation of dense accumulation of defects. The onset of COD has been experimentally connected to critical temperatures in the range 120–200°C, which must be reached so that the thermal runaway takes place.[2–4] The values of these experimental temperatures should be handled with care, as the size of the experimental probes with which these temperatures are measured is orders of magnitude larger than the active layers of the lasers, where the hot regions are locally generated.[5] Over the years, various physico-mathematical models have been proposed to explain the root causes of COD.[6–9] Our approach basically differs from those previous models on the
relevant role that the mechanical degradation of the device plays for the onset of COD. The catastrophic degradation is described in terms of re
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