Typical for broad-area laser (BAL) diodes operating in a continuous-wave mode is a narrowing of the near-field (NF) width at the output facet for high injection currents (output powers). This phenomenon increases the facet load of BALs, resulting in a reduction in the level of catastrophic optical mirror damage. In this letter, we demonstrate theoretically that thermally induced changes in the refractive index in both lateral and longitudinal directions not only cause the NF narrowing at the front facet but also a broadening of the NF at the back facet. In contrast, a sole lateral self-heating induced variation in the refractive index (commonly referred to as thermal lensing) does not result in a NF narrowing. Our theoretical findings are confirmed by measurements of the current-dependent profiles of the NF at the back and front facets of a BAL with a stripe width of 120 μm emitting at 960 nm. Furthermore, our quasi three-dimensional thermo-electro-optic simulations indicate that a longitudinally homogeneous device temperature can reduce the front-facet load while keeping the beam quality unchanged compared with the experimental results.

We report on individual wavelength locking of a multiplet of 100-μm broad-area laser diode emitters arranged on a 50% fill-factor bar by means of a single external multi-laser cavity using an ultra-narrowband thin-film filter as a dispersive optical element. The achieved wavelength-locked output power is 216 W, corresponding to an electrical-to-optical conversion efficiency of about 49.7%. The 45 emitters of the laser diode bar are stabilized within a spectral range of about 6.4 nm. Our approach is suited for killowatt-class dense wavelength beam combining of direct diode lasers.

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