  Ultrafast laser systems operating with high-average power in the wavelength
range from 1.9 um to 3 um are of interest for a wide range of applications for
example in spectroscopy, material processing and as drivers for secondary
sources in the XUV spectral region. In this area, laser systems based on
holmium-doped gain materials directly emitting at 2.1 um have made significant
progress over the past years, however so far only very few results were
demonstrated in power-scalable high-power laser geometries. In particular, the
thin-disk geometry is promising for directly modelocked oscillators with high
average power levels that are comparable to amplifier systems at MHz repetition
rate. In this paper, we demonstrate Semiconductor Saturable Absorber Mirror
(SESAM) modelocked Ho:YAG thin-disk lasers (TDLs) emitting at 2.1 um wavelength
with record-holding performance levels. In our highest average power
configuration, we reach 50 W of average power, with 1.13 ps pulses, 2.11 uJ of
pulse energy and ~1.9 MW of peak power. To the best of our knowledge, this
represents the highest average power, as well as the highest output pulse
energy so far demonstrated from a modelocked laser in the 2 um wavelength
region. This record performance level was enabled by the recent development of
high-power GaSb-based SESAMs with low loss, adapted for high intracavity power
and pulse energy. We also explore the limitations in terms of reaching shorter
pulse durations at high power with this gain material in the disk geometry and
using SESAM modelocking, and present first steps in this direction, with the
demonstration of 30 W of output power, with 692 fs pulses in another laser
configuration.
