The limits to the continuous-wave (CW) output power of the GaAs-based high-power diode lasers with an asymmetric photon density along the resonator are experimentally investigated. Spontaneous emission measurement in CW mode and electro-optical characterization both in CW and short pulse mode have been performed to clarify the impact of temperature, bias, and photon density profile on CW output power. Diode lasers with a 90 µm stripe and 6 mm resonator have been fabricated with a backside metallization window along the resonator to measure spontaneous emission intensity (and hence relative carrier density) profile and wavelength to infer temperature. Also, the longitudinal photon density profile has been varied using 98% rear facet reflectivity and 0.8% and 20% front facet reflectivities. Spontaneous emission data demonstrates that asymmetric photon density leads to non-uniform carrier density with higher carrier density at the back facet and increasing temperature at the front compared to the back facet, due to the longitudinal spatial hole burning (LSHB) effect, which becomes more severe with bias. Spontaneous emission data also shows that carriers accumulate at the front facet stripe edges, which can be attributed to the higher temperature at the front facet and lateral spatial hole burning. Further, light-current characteristics in pulse mode show that non-uniform carrier density triggers losses at high temperatures, increasing threshold and reducing internal efficiency. The reduction in internal efficiency becomes much larger in CW operation, due to the large lateral and longitudinal local temperature variations, which lead to strong carrier accumulation at the front stripe edges.
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