COD is an irreversible process is in which the laser facet or the bulk of the semiconductor melts due to a strong absorption of light. This happens due to a high light density, a high density of non-radiative recombination centers or a combination of both. Due to the abovementioned effect of heat on the energy bands, this effect tends to reinvigorate itself quickly creating so much heat in a very small portion of the semiconductor crystal or the facet, that it actually physically melts, locally destroying the laser diode.
To increase the COD power levels on a laser design is challenging and it includes beam expansion to reduce local light intensity. By placing special attention on the epitaxial growth process and the facets, significant improvements can be achieved.