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13 February 2008 Emitter resolved analysis of packaged laser bars
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Thermo-mechanical stress occurring during the packaging process and during operation limits the reliability of high-power diode laser bars. The stress is caused by the mismatch of the thermal expansion coefficients between the heat sink and laser bar material. A soft solder layer can partially reduce the stress by relaxation. A convenient approach for reducing the stress is the matching of the thermal expansion of the heat sink to the laser bar material. The disadvantage of most expansion-matched heat sinks is a higher thermal resistance so that the device temperature increases and the lifetime decreases. For the development of thermal and strain optimized diode laser packages an analysis of both the thermal and strain distribution is reasonable. In this work the strain is analyzed by electroluminescence using the correlation between stress and the polarization properties of the laser bar radiation. This method allows a qualitative emitter resolved strain mapping along the slow-axis. Because of the correlation between temperature and wavelength a thermal analysis of mounted laser bars can be done by an emitter resolved spectral mapping. Irregularities in the thermal contact between laser bar and heat sink such as defects in the solder layer become visible by irregular emitter spectra. The work shows examples for the optimization of the package. The analysis of the thermal and strain distribution shows the advantages and disadvantages of the particular approaches, like variations of solder thickness or expansion matched packages.
© (2008) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Thomas Westphalen, Michael Leers, Christian Scholz, and Konstantin Boucke "Emitter resolved analysis of packaged laser bars", Proc. SPIE 6876, High-Power Diode Laser Technology and Applications VI, 68760O (13 February 2008);

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