High power broad-area diode lasers are the most efficient source of optical energy, but cannot directly address many applications due to their high lateral beam parameter product BPP = 0.25 × Θ_L ^95%× W_95% (Θ_L^95% and W_95% are emission angle and aperture at 95% power content), with BPP > 3 mm×mrad for W_95%~90μm. We review here progress within the BRIDLE project, that is developing diode lasers with BPP < 2 mm×mrad for use in direct metal cutting systems, where the highest efficiencies and powers are required. Two device concepts are compared: narrow-stripe broad-area (NBA) and tapered lasers (TPL), both with monolithically integrated gratings. NBAs use W_95% ~ 30 μm to cut-off higher order lateral modes and reduce BPP. TPLs monolithically combine a single mode region at the rear facet with a tapered amplifier, restricting the device to one lateral mode for lowest BPP. TPLs fabricated using ELoD (Extremely Low Divergence) epitaxial designs are shown to operate with BPP below 2mm×mrad, but at cost of low efficiency (<35%, due to high threshold current). In contrast, NBAs operate with BPP < 2 mm×mrad, but maintain efficiency >50% to output of > 7 W, so are currently the preferred design. In studies to further reduce BPP, lateral resonant anti-guiding structures have also been assessed. Optimized anti-guiding designs are shown to reduce BPP by 1 mm×mrad in conventional 90 μm stripe BA-lasers, without power penalty. In contrast, no BPP improvement is observed in NBA lasers, even though their spectrum indicates they are restricted to single mode operation. Mode filtering alone is therefore not sufficient, and further measures will be needed for reduced BPP.

Date Published: 13 March 2015
PDF: 11 pages
Proc. SPIE 9348, High-Power Diode Laser Technology and Applications XIII, 93480D (13 March 2015); doi: 10.1117/12.2077617

Published in SPIE Proceedings Vol. 9348:
High-Power Diode Laser Technology and Applications XIII
Mark S. Zediker, Editor(s)