Longitudinal spatial inhomogeneities in high-power semiconductor lasers

We study the spatial distribution of the temperature, gain, and carrier density along the longitudinal direction of a semiconductor laser cavity. In high-power laser diodes, the use of asymmetrical facet reflectivities creates a spatially nonuniform photon intensity profile and results in inhomogeneous temperature and carrier distributions along the active stripe. These profiles are determined from direct measurements of blackbody radiation and the spontaneous emission from the laser cavity. The temperature of the active stripe is observed to be significantly higher than that of the heat sink during lasing, and the effect of temperature on the modal gain spectrum is analyzed. We demonstrate that the local carrier density and optical gain within a laser are not pinned beyond threshold. A spatially inhomogeneous gain profile is possible in laser cavities as long as the threshold condition that the averaged round-trip gain equals the total losses is maintained. A theoretical model is presented which explains the observed experimental data.>