  We present the experimental realization of spectrally tunable, ultrashort,
quasi-monochromatic extreme ultraviolet (XUV) pulses generated at 100 kHz
repetition rate in a user-oriented gas high harmonic generation (GHHG) beamline
of the Extreme Light Infrastructure - Attosecond Light Pulse Source (ELI ALPS)
facility. Versatile spectral and temporal shaping of the XUV pulses are
accomplished with a double-grating, time-delay compensated monochromator
accommodating the two composing stages in a novel, asymmetrical geometry. This
configuration supports the achievement of high monochromatic XUV flux
(2.8+/-0.9*1e10 photons/s at 39.7 eV selected with 700 meV FWHM bandwidth)
combined with ultrashort pulse duration (4.0+/-0.2 fs using 12.1+/-0.6 fs
driving pulses) and small spot size (sub-100 um). Focusability, spectral
bandwidth, and overall photon flux of the produced radiation were investigated
covering a wide range of instrumental configurations. Moreover, complete
temporal (intensity and phase) characterization of the few-femtosecond
monochromatic XUV pulses - a goal that is difficult to achieve by conventional
reconstruction techniques - has been realized using ptychographic algorithm on
experimentally recorded XUV-IR pump-probe traces. The presented results
contribute to in-situ, time-resolved experiments accessing direct information
on the electronic structure dynamics of novel target materials.
