  We report on a monolithic thulium fiber laser with 567 W output power at 1970
nm, which is the highest power reported so far directly from a thulium
oscillator. This is achieved by optimization of the splice parameters for the
active fiber (minimizing signal light in the fiber cladding) and direct water
cooling. Dual transverse mode operation is visible from the optical spectrum
and can also be deduced from the measured beam quality of M^2 = 2.6.
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