Tailored in-plane thermal profiles for narrower lateral far-field in kilowatt-class 9xx nm diode laser bars

Miah, Md. Jarez; Karow, Matthias M.; Elattar, Mohamed; Martin, Dominik; Della Casa, Pietro; Grützner, Stefan; Strohmaier, Stephan; Knigge, Andrea; Crump, Paul A.; Tränkle, Günther

doi:10.1117/12.2648355

Cited by 3 publications

References 15 publications

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Experimental and theoretical studies into longitudinal spatial hole burning as a power limit in high-power diode lasers at 975 nm

Arslan

Wenzel

Fricke

et al. 2023

Applied Physics Letters

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Spatial-hole-burning as a limit to the continuous-wave (CW) output power of GaAs-based diode lasers is experimentally studied. For 90 μm stripe lasers with 6 mm resonator length and 0.8% front facet reflectivity, spontaneous emission (SE) intensity data show that the carrier density in the device center rises rapidly at the rear facet with bias and falls at the front, consistent with simulation. At the front, the carrier density at the edge of the laser stripe also rises rapidly with bias (lateral carrier accumulation, LCA), consistent with previous observations of increased local current flow. Devices with 20% front facet reflectivity for a flat longitudinal optical field profile show smaller variation in the local carrier density. Weak variation is seen in the carrier density outside the stripe; hence, current spreading is not a power limit. SE wavelength data show higher temperatures at the front with a twofold higher increase in temperature for 0.8% than for 20% front facet. The increased front temperature likely triggers lateral spatial-hole-burning and LCA in this region, limiting power. Finally, pulsed threshold current is more strongly temperature dependent for devices with 0.8% than 20% front facets, attributed to the higher rear facet carrier density. The temperature dependence of slope in pulsed is comparable for both devices at low bias but is more rapid for 0.8% at 20 A, likely due to non-clamping at the back. The temperature dependence of slope for CW is strong with 0.8% facets, likely due to the high temperature and LCA at the front but reduced for 20% facets.

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Experimental and theoretical studies into longitudinal spatial hole burning as a power limit in high-power diode lasers at 975 nm

Arslan

Wenzel

Fricke

et al. 2023

Applied Physics Letters

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Micro-structured lateral thermal lens for increased output power and narrowed beam divergence in kilowatt-class 9xx nm diode laser bars

Miah,

Martin,

Ginolas

et al. 2024

Applied Physics Letters

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Local temperature non-uniformity is a critical limit to power in large-area semiconductor lasers, playing a larger role than the conversion efficiency and temperature sensitivity in the most efficient modern devices. For the specific case of kilowatt-level edge-emitting diode laser bars, we demonstrate that laterally re-distributing current locally within each emitter using a customized micro-structuring of the electrical contact can flatten the thermal profile, based on the thermal design using COMSOL. The concept is demonstrated experimentally in adapted bars that contain eight broad-area emitters, each having wide (∼1100 μm) stripes and a 4 mm long resonator. Each emitter in the laser bar has an electrical contact layer that is electrically structured into parallel sub-contacts using implantation, essential to prevent lateral lasing, implemented here with a period of 29 μm. The width of the individual sub-contacts is narrowed in the device center and then monotonically increased toward the emitter edges to collect a higher proportion of heat at the edges, for a fivefold reduction in the thermal lens, despite a significant (20%) overall increase in electrical and thermal resistance. Two performance benefits are observed. First, the slope varies more slowly with average temperature, recovering (here) around half of the efficiency penalty from in-stripe temperature non-uniformity, and hence increasing the power conversion efficiency at 800 W optical output power by around 5%. Second, the lateral far field (95% power content) is narrowed by around 2° at 800 W optical output power, corresponding to a reduction of around half of the thermal contribution.

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Improved efficiency and beam divergence in kW-class diode laser bars with edge-heaters

Miah,

Boni,

Martin

et al. 2024

2024 IEEE Photonics Conference (IPC)

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Tailored in-plane thermal profiles for narrower lateral far-field in kilowatt-class 9xx nm diode laser bars

Cited by 3 publications

References 15 publications

Experimental and theoretical studies into longitudinal spatial hole burning as a power limit in high-power diode lasers at 975 nm

Experimental and theoretical studies into longitudinal spatial hole burning as a power limit in high-power diode lasers at 975 nm

Micro-structured lateral thermal lens for increased output power and narrowed beam divergence in kilowatt-class 9xx nm diode laser bars

Improved efficiency and beam divergence in kW-class diode laser bars with edge-heaters

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