A narrow bandwidth extreme ultra-violet light source for time- and angle-resolved photoemission spectroscopy

Here we present a high repetition rate, narrow band-width, extreme ultraviolet (XUV) photon source for time- and angle-resolved photoemission spectroscopy (tr-ARPES). The narrow band width pulses $\Delta E=9, 14, 18$ meV for photon energies $h<br>u=10.8, 18.1, 25.3$ eV are generated through High Harmonic Generation (HHG) using ultra-violet (UV) drive pulses with relatively long pulse lengths (461 fs). The HHG setup employs an annuluar drive beam in a tight focusing geometry at a repetition rate of 250 kHz. Photon energy selection is provided by a series of selectable multilayer bandpass mirrors and thin film filters, thus avoiding any time broadening introduced by single grating monochromators. A two stage optical-parametric amplifier provides $< 100$ fs tunable pump pulses from 0.65 $\mu$m to 9 $\mu$m. The narrow bandwidth performance of the light source is demonstrated through ARPES measurements on a series of quantum materials including the high-temperature superconductor Bi-2212, WSe$_2$ and graphene.