Experimental Studies into the Beam Parameter Product of GaAs High-Power Diode Lasers
IEEE J. Sel. Top. Quantum Electron., vol. 28, no.1, pp. 1501111 (2022).
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Experimental studies into the beam parameter product (BPP) of 940–980 nm GaAs-based high-power diode lasers are presented. Such lasers exhibit broadening far field and narrowing near field with increasing bias, with BPP increasing tenfold over the diffraction limit. First, spectrally-resolved beam profile measurements of lasers with monolithically-integrated gratings are presented, showing that a reproducible series of spatially-extended optical modes makes up the optical field. Then, changes to the device construction are presented, enabling effects limiting BPP to be inferred and addressed. Process- and package-induced effects can be minimized by design, while the effects of carrier, gain and temperature profiles dominate. Self-heating within the laser stripe raises the refractive index, forming a thermal lens, and the variation in curvature of this lens with bias and device construction directly affects BPP. Temperature non-uniformity along the resonator is also shown to strongly degrade BPP. Moreover, current spreading and the resulting lateral carrier accumulation (LCA) amplify high-order, high-BPP modes, thus degrading BPP for any given thermal lens. This LCA-induced degradation is shown to be suppressed by regrown lateral current-blocking structures. Finally, a flatter thermal lens and lower BPP can be achieved using thermal engineering, via changes to the epitaxial design or device layout.
1 Ferdinand-Braun-Institut gGmbH, Leibniz Institut für Höchstfrequenztechnik (FBH), 12489 Berlin, Germany
2 TRUMPF Laser GmbH
Distributed feedback devices, Quantum well lasers, Far field, Near field, Semiconductor device thermal factors, High-power lasers, Energy conversion, Multimode waveguides.