The high optical power causes a non-negligible heating of the active parts, quantum well (QW) and surrounding layers, particularly at the facet mirrors, where energy losses take place. The heating induces a degradation of the output power, and is eventually responsible for COD. How temperature control directly influences output stability, aging behaviour, and long term reliability in industrial, scientific and medical laser applications. Laser performance does not degrade randomly. In most systems, temperature is the dominant factor that determines stability, optical. If an excessive current flows in a laser diode, a large optical output is generated occur and the emitting facet may be damaged. This optical damage can happen even with a momentary over-current. A summary of the methods used to assess the COD, both in real time and post-mortem is presented.
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