Ultrafast polarization-tunable monochromatic extreme ultraviolet source at high-repetition-rate

Abstract

We report on the development of a high-order harmonic generation (HHG)-based ultrafast high-repetition-rate (250~kHz) monochromatic extreme ultraviolet (21.6~eV) source with polarization tunability, specifically designed for multi-modal dichroism in time- and angle-resolved photoemission spectroscopy. Driving HHG using an annular beam allows us to spatially separate the high-power 515~nm driving laser from the XUV beamlet while preserving the linear polarization axis angle tunability. This enables controlling the polarization state of the XUV radiation with a fixed all-reflective phase-shifter. This scheme leads to a source brightness of 5.7$\times$10$^{12}$ photons/s at 21.6~eV (up to 4$\times$10$^{11}$ photons/s on target) with ellipticities as high as 90$\%$.