About the critical temperature for catastrophic optical damage in high power laser diodes

Abstract

Degradation of laser diodes during operation constitutes a serious drawback for both laser manufacturers and end users. The catastrophic optical damage (COD) of laser diodes consists of the sudden drop off of the optical power. COD involves a thermal runaway mechanism in which the active zone of the laser is molten. Degraded devices present dark line defects (DLDs) produced during the laser operation; these DLDs are regions of the active zone of the laser without emission. These dark lines are locally generated, either at the front facet, or inside the cavity, and then propagate along the cavity driven by the optical field. The physical mechanism leading to the formation of such lines and the associated loss of output optical power is described in the literature, but there is not consensus about the origin of the COD. Usually, the COD is described in a sequence of different phases, in the first phase the process is incubated, this phase ends when a critical temperature is reached; then, it is followed by a sharp increase of the optical absorption with the corresponding sharp temperature increase which leads to melting and the failure of the device. Here we will focus on the first phase, we will discuss about the critical temperature, and the physical mechanisms involved in this phase; in particular, we will describe the conditions under which such critical temperature can be reached. For this we will analyze the conditions for reaching the critical temperature and the influence of the laser structure on the laser strength. We compare the critical temperature estimated by our thermomechanical model with the values experimentally reported, which range between 130ºC and 180ºC.