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An analytical, two-dimensional, stationary model of heat distribution in a broad-area laser is discussed. In the model the laser is treated as a stack of layers of different thicknesses and thermal conductivities. We show how to adjust the geometry of such a stack to take into account a non-ideal heat sink (made of material of finite thermal conductivity) and thus obtain reliable values of the device temperature. The calculated and measured thermal resistances of an exemplary laser series are compared. Our experiment is based on the analysis of a spectral shift of the laser radiation, which provides information about the mean temperature of the active region. A discussion of different types of bonding imperfections and their influence on the obtained results is provided.

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Multispectral infrared (IR) imaging is used for reliability screening of diode lasers. The signal detected by the camera in the near IR region is found to be mainly affected by midgap deep level luminescence, whereas the thermal radiation is the main signal contribution in the mid IR. The information from both spectral channels is used for preselection of potentially long-lived devices. The devices with enhanced luminescence from deep levels and elevated temperature of the active region are the candidates for faster degradation. Defects such as hot spots can be discarded extremely quickly by using thermographic inspection. The thermographic results are complemented with spectral Fourier transform photocurrent measurements and low-current I-V characterization. The results of aging experiments of diode lasers are presented. A correlation between measurements of unaged devices and lifetest results is found and discussed in detail. The proposed preselection methodology is an alternative to conventional burn-in tests for high-power diode lasers.