Catastrophic optical damage
Catastrophic optical damage (COD), or catastrophic optical mirror damage (COMD), is a failure mode of high-power semiconductor lasers. It occurs when the semiconductor junction is overloaded by exceeding its power density and absorbs too much of the produced light energy, leading to melting and recrystallization of the semiconductor material at the facets of the laser. This is often colloquially referred to as "blowing the diode." The affected area contains a large number of lattice defects, negatively affecting its performance. If the affected area is sufficiently large, it can be observable under optical microscope as darkening of the laser facet, and/or as presence of cracks and grooves. The damage can occur within a single laser pulse, in less than a millisecond. The time to COD is inversely proportional to the power density. Catastrophic optical damage is one of the limiting factors in increasing performance of semiconductor lasers. It is the primary failure mode for AlGaInP/AlGaAs red lasers. Short-wavelength lasers are more susceptible to COD than long-wavelength ones. The typical values for COD in industrial products range between 12 and 20 MW/cm2. Causes and mechanisms At the edge of a diode laser, where light is emitted, a mirror is traditionally formed by