Root cause investigation of back-irradiance-induced failure of high power diode lasers

Back-irradiance testing of high power diode lasers with absorbing substrates reveals catastrophic failure occurs when the return spot is shifted slightly with respect to the quantum well (into the substrate). Thermoreflectance temperature mapping shows this position to be the point of maximum facet temperature rise at the active region. Finite element thermal modelling, which is in close agreement with thermoreflectance results, indicates a root cause of thermal cross-heating between the absorbed back-irradiance light in the substrate and heating in the active region.