Contents I. Introduction
The brightness of a semiconductor laser array is an important parameter for many applications, including pumping fiber lasers, target illumination, and materials processing. In the case of fiber pumping, the output power of kilowatt-class ytterbium-doped silica fiber lasers is commonly limited by the available pump brightness [1]. This property is especially of importance for all-glass double-clad fiber lasers, with relatively low numerical apertures. Nearly diffraction-limited high-power output from diode laser arrays would be an enabling capability for many potential direct-diode applications, including target illumination and materials processing. In these applications, the availability of low divergence beams directly from diode arrays would allow for high efficiency diode lasers to be used directly, without the need for a solid state or fiber laser stage. Additionally, the high degree of collimation would maximize the power on the far-field target, or equivalently, power in the bucket. We have been developing two key technologies for achieving high-brightness, direct-diode laser arrays. These technologies are high-brightness slab-coupled optical waveguide laser (SCOWL) arrays [2], [3] and wavelength beam combining (WBC) [4]. SCOWL devices are nearly ideal sources for beam combination using WBC. In contrast to conventional ridge waveguide lasers, SCOWL devices feature large ( and larger) nearly circular fundamental modes. The large optical mode is enabled by mode filtering of higher order modes in the large waveguide via slab coupling. Greater than 1-W continuous-wave (CW) output power has been obtained with beam quality parameters for both 915- and 975-nm SCOWL devices [5], [6]. In addition, SCOWL devices are suitable for high-power linear arrays [3].
