High-power red-emitting lasers with high reliability are strongly desired by applications like photodynamic therapy. Semiconductor lasers based on AlGaInP have emerged as the best candidates in this spectral range. However, compared to infrared emitters, high-power performance is still limited by major degradation effects, especially by catastrophic optical damage (COD). An innovative combination of concepts, namely microphotoluminescence (µPL) mapping, focused ion beam (FIB) microscopy, micro-Raman spectroscopy, and high-speed thermal imaging has been employed to reveal the physics behind COD, its related temperature dynamics, as well as associated defect and near-field patterns. µPL showed that COD-related defects are composed of highly nonradiative complex dislocations, which start from the output facet and propagate deep inside the cavity. Moreover, FIB analysis confirmed that those dark line defects are confined to the active region, including the quantum wells and partially the waveguide. In addition, the COD dependence on temperature and power was analyzed in detail by micro-Raman spectroscopy and thermal imaging. For AlGaInP lasers in the whole spectral range of 635 to 650 nm, it was revealed that absorption of stimulated photons at the laser output facet is the major source of facet heating, and that a critical facet temperature must be reached in order for COD to occur. A linear relationship between facet temperature and near-field intensity has also been established. This understanding of the semiconductor physics behind COD is a key element for further improvement in output power of AlGaInP diode lasers.