  Extreme ultraviolet (XUV) lasers are essential for the investigation of
fundamental physics. Especially high repetition rate, high photon flux sources
are of major interest for reducing acquisition times and improving signal to
noise ratios in a plethora of applications. Here, an XUV source based on
cascaded frequency conversion is presented, which delivers due to the drastic
better single atom response for short wavelength drivers, an average output
power of (832 +- 204) {\mu}W at 21.7 eV. This is the highest average power
produced by any HHG source in this spectral range surpassing precious
demonstrations by more than a factor of four. Furthermore, a narrow-band
harmonic at 26.6 eV with a relative energy bandwidth of only {\Delta}E/E= 1.8 x
10E-3 has been generated, which is of high interest for high precision
spectroscopy experiments.
