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The quest for mapping the femtosecond dynamics of the electronic bandstructure of complex materials via Time- and Angle-Resolved PhotoelectronSpectroscopy (TR-ARPES) over their full First Brillouin Zone is pushing thedevelopment of schemes to efficiently generate ultrashort photon pulses in theVUV-range of photon energies. At present, the critical aspect is to combine ahigh photon energy with high photoemission count rates and a smallpulse-bandwidth, necessary to achieve high energy resolution in ARPES, whilepreserving a good time resolution and mitigating space-charge effects. Here wedescribe a novel approach to produce light pulses at 10.8 eV, combining highrepetition rate operation (1-4 MHz), high energy resolution ($\sim26$ meV) andspace-charge free operation, with a time-resolution of $\sim$700 fs. Theseresults have been achieved by generating the 9th harmonic of a Yb fiber laser,through a phase-matched process of third harmonic generation in Xenon of thelaser third harmonic. The full up-conversion process is driven by a seed pulseenergy as low as 10 $\mu$J, hence is easily scalable to multi-MHz operation.This source opens the way to TR-ARPES experiments for the investigation of theelectron dynamics over the full first Brillouin zone of most complex materials,with unprecedented energy and momentum resolutions and high count rates. Theperformances of our setup are tested in a number of experiments on WTe$_2$ andBi$_2$Se$_3$, of which we measure the electronic band structure in energy,two-dimensional momentum and time.

High repetition rate Time-Resolved VUV ARPES at 10.8 eV photon energy