The two-dimensional (2D) temperature profile of a high-power junction-down broad-area diode laser facet subject to back-irradiance (BI) is studied via CCD-based thermoreflectance (TR) imaging and finite element modeling. The temperature rise in the active region (ΔΤAR) is determined at different diode laser optical powers, back-irradiance reflectance levels, and back-irradiance spot locations. Interestingly, our study shows that ΔΤAR rises sharpest not when the back-irradiance is boresight-aligned with the active region but rather when it is centered in the absorbing substrate approximately 5 μm away from the active region, a distance roughly equal to half of the back-irradiance spot FWHM (9 μm). At this critical location, ΔΤAR is found to increase by nearly a factor of three compared to its increase without back-irradiance. This provides insight on an important location for back-irradiance that may be correlated with catastrophic optical damage (COD) for diode lasers fabricated on absorbing substrates, and also suggests a thermal basis for truncated lifetime and deegraded performance for diode lasers experiencing backirradiance.
Chen Li, Kevin P. Pipe, Chuanshun Cao, Prabhu Thiagarajan, Robert J. Deri, and Paul O. Leisher, "CCD-based thermoreflectance imaging of high-power diode lasers with back-irradiance," Proc. SPIE 10637, Laser Technology for Defense and Security XIV, 106370C (Presented at SPIE Defense + Security: April 17, 2018; Published: 4 May 2018); https://doi.org/10.1117/12.2302434.
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