We present highly efficient high power single longitudinal mode waveguide lasers. Single mode operation was achieved by combining a tapered waveguide Bragg grating with a Yb:YAG crystalline waveguide laser in a hybrid approach. Both structures were fabricated by fs-laser writing. We achieved 1.59 W of output power in a single longitudinal mode and 4.71 W of output power with a spectral bandwidth of 38 pm. The slope efficiency was 66% and the laser threshold 92 mW.