Catastrophic optical damage (COD) of high power laser diodes is a crucial factor limiting
ultra high power lasers. The understanding of the COD process is essential to improve the
endurance of the high power laser diodes. COD is observed as a process in which the active
part of the laser diode is destroyed, forming characteristic defects, the so called dark line
defects (DLDs). The DLDs are formed by arrays of dislocations generated during the laser
operation. Local heating associated with non-radiative recombination is assumed to be at the
origin of the COD process. A summary of the methods used to assess the COD, both in real
time and post-mortem is presented. The main approaches developed in recent years to model
the heat transport in the laser structures under non homogeneous temperature distribution are
overviewed. Special emphasis is paid to the impact of the low dimensionality of QWs in two
physical properties playing a major role in the COD process, namely, thermal conductivity
and mechanical strength. A discussion about the impact of the nanoscale in both physical
properties is presented. Finally, we summarize the main issues of the thermomechanical
modelling of COD. Within this model the COD is launched when the local thermal stresses
generated around the heat source overcome the yield stress of the active zone of the laser. The
thermal runaway is related to the sharp decrease of the thermal conductivity once the onset of
plasticity has been reached in the active zone of the laser.
