Spectrally stabilized and combined diode lasers

Dense wavelength beam combining (DWBC) of hundreds to thousands of few-power broad-area laser diode (BAL) emitters into a single high-power laser beam is a promising approach to establish direct diode lasers in classical multi-kW high-brightness laser applications, such as e.g. 2D-flatsheet metal cutting or remote laser welding. Compared to dissipative optically pumped solid-state lasers, direct diode lasers potentially exhibit enhanced electrical-to-optical (eo) conversion efficiencies of up to 45% or higher allowing customers to lower their costs of ownership. Aside from economic aspects, such beam sources are thought being ultra-compact. However, competitive costs and equivalent reliability with respect to well established solid-state lasers will be the ultimate prerequisites for a successful market penetration. During the past decade many research and development activities in this field have been undertaken to build industrial high-brightness direct diode lasers [1-3], but it has only been quite recently that the DWBC technology appears to come of age. In this paper, we introduce our approach to DWBC which relies on an open-loop design, implying a decoupling of the wavelength-stabilizing multi-laser cavity and the beam combining diffraction grating. We will describe the underlying principle and show high power results at the 500 W output power level. We will further highlight technological obstacles seen throughout the research and development of our specific approach as well as generic detrimental characteristics of DWBC of BALs which might limit the technology when it comes down to further power and brightness scaling in the future.