Thermal processes in high-power laser bars investigated by spatially resolved thermoreflectance

The implementation of the thermoreflectance technique for the analysis of facet heating in commercial high-power laser bars is demonstrated. The technique provides highly spatially resolved information about facet temperature along the active stripes of all the emitters in the bar. The recorded maps reveal multiple hot-spots localized in the active area region of the laser structure. Apart from the thermoreflectance, thermal properties of the laser bar are studied by two complementary thermometric techniques: IR thermography which provides fast information about temperature profiles and hot spot location, and wavelength tuning technique which is used to determine the time-resolved bulk temperature for all emitters in the bar. Analysis of the results obtained by different methods indicates that the observed local overheating is related to defects starting at the laser facet or very close to the facet. The thermal data for non-degraded emitters, on the other hand, shows a moderate facet overheating of 5−12 °C (for the laser bar operating under quasicontinuous-wave conditions).