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This Small Business Innovation Research (SBIR) Phase II project is aimed at achieving the first ever 350W (cw) output power in a high brightness and diffraction-limited laser beam from a multicore phase-locked fiber laser array. Under Phase I, the feasibility of the unique power combining concept has been demonstrated by phase-locking a group of 7 Yb-doped single mode fiber lasers, embedded in a common cladding. In addition, a theoretical model has been developed, providing a deeper understanding of physical mechanisms responsible for phase-locking of a multicore fiber laser array. These results clearly indicate that this extremely challenging goal for Phase II can be accomplished. Nevertheless, there remain several obstacles that need to be removed before embarking on commercialization. First, a significant improvement of the laser performance must be made. This can be accomplished by exploring various parameters, which include fiber length, cavity finesse, gain saturation, temperature and stress distributions, as well as fiber structural parameters, such as core separation and the V-value. In addition, an order of magnitude improvement for efficient coupling of pump power into the clad must be made. To advance this technology, various pumping techniques will be explored, in particular the side-pumping of the fiber laser from the cladding walls, instead of the fiber end facets. If successfully developed, this could be the most viable way to obtain the maximum output power without causing catastrophic damage. Finally, the reliability of the device when operating at very high power level must be established by raising the power damaging threshold. High power diode-pumped multicore fiber lasers can be very competitive in the market place as compared to high power diode-pumped solid-state lasers and C02 lasers presently employed by automotive, aerospace and ship-building industries for precision drilling, high-speed cutting and welding of metals and composition materials.