Nondestructive, in situ infrared imaging of line defect growth in high-power diode laser cavities

Using a high sensitivity infrared camera, we image the optical cavity of an operating high-power diode laser through a window etched in the substrate and observe weak IR emission from the waveguide core region. The IR intensity maps show dark spots in the cavity that subsequently grow into line defects (all oriented in the same direction) as the laser ages. This technique holds promise as a nondestructive, in situ approach to study the formation and evolution of defects in an operating device. We also use CCD-based thermoreflectance to generate high-resolution facet temperature profiles of the same lasers during aging, with the results suggesting that the slow degradation of optical power that occurs prior to laser failure relates more to cavity defect formation than facet defect (hotspot) formation.