Mapping of local temperatures on mirrors of GaAs/AlGaAs laser diodes

Abstract

Spatially resolved Raman scattering measurements (<1 μm) have been performed to determine the surface temperature distribution on coated and uncoated facets of ridge-waveguided GaAs/AlGaAs single quantum well graded-index separate-confinement heterostructure lasers. A strong nonlinear temperature versus output-power dependence is observed for cleaved, uncoated mirrors (ΔT>100 K for P>1 MW/cm2). Raman line scans show hot spot regions at the facets. Degradation strength correlates with facet heating. Disorder-activated Raman phonon modes indicate strong crystal damage. Laser mirrors with λ/2-Al2O3 coatings withstand up to 4-5 times the power density without significant heating and degradation. Local electroluminescence measurements along the cavity confirm increasing temperatures when approaching the facets and show that the resonator bulk material remains cold (ΔT<5 K).