The versatility and usefulness of the newly developed reflectance modulation technique for laser mirror characterization will be demonstrated by means of typical examples of application on (110) facets of 10-mu-m wide ridge waveguide AlGaAs/GaAs quantum well lasers: (1) Typical, maximum temperature increases DELTA-T derived from the reflectance changes DELTA-R/R are congruent-to 1 K per 1 mW optical diode power for uncoated mirrors and are congruent-to 10x lower for lambda/2-Al2O3 coated ones. DELTA-T is sensitive to the facet surface treatment prior to coating. (2) Temperature maps show a very localized hot spot within the near-field region and are in accordance with our two-dimensional heat flow calculations. (3) Degradation processes have been monitored in real time. Thus, we determined a critical temperature increase DELTA-T congruent-to 120 K for the occurrence of catastrophic optical mirror damage in the AlGaAs system.