Investigation of thermal processes in high power laser bars by thermoreflectance spectroscopy

In this paper we present results of the analysis of the thermoreflectance (TR) measurements performed on the high power laser diodes and laser bar emitting at 808 nm. Thermoreflectance is a modulation technique relying on periodic facet temperature modulation induced by pulsed current supply of the laser. The periodic temperature change of the laser induces variation of the refractive index and consequently modulates probe beam reflectivity. Spatially resolved thermoreflectance spectroscopy is applied to measure line-scans and maps of temperature distribution at the laser mirrors and emitter facets in laser bar. However, to get the absolute values of temperatures, thermoreflectance needs calibration. Different calibration methods, such us: mu-Raman spectroscopy and in situ determination of thermoreflectance coefficient (CTR) will be discussed. The knowledge of temperature distribution at laser facets gives insight into thermal processes occurring at devices' facets and consequently leads to the increased reliability and substantially longer lifetimes of such structures.