Comparison of catastrophic optical damage events in GaAs- and GaN-based diode lasers

Damage patterns caused by Catastrophic Optical Damage (COD) are analyzed in GaN-based high-power diode lasers. We find the process to result in material loss including the formation of an empty channel. This is consistent with the observation of ejections of hot material out of the front facet of the device during COD. In the immediate vicinity of the empty channel, the laser structure seems to be absolutely undisturbed. These results are compared with earlier results from comparable experiments obtained with GaAs-based devices. While the COD process in both material systems follows similar scenarios and root causes, the damage pattern differs substantially. The completely empty channel at the position of the optical mode is in striking contrast to the results of earlier studies in GaAs-based devices, degraded under almost identical conditions. There molten, phase segregated, and both recrystallized and amorphous materials with well-pronounced melting fronts are observed. In the GaN-based devices we observe average defect front propagation velocities along the laser axis of 110 m/s. This is faster by a factor of 4-5 than what has been observed in GaAs-based devices under comparable experimental conditions.