High-Repetition-Rate Extreme Ultraviolet Beamlines at the Artemis Facility

Artemis is a mid-scale extreme ultraviolet (XUV) laser science laboratory at the UK’s Central Laser Facility (CLF), which provides users access to cutting-edge femtosecond dynamics in gas-phase and solid-state systems via photoemission spectroscopy. We have recently commissioned a 100-kHz 200-W high-repetition-rate Yb-based laser system based on optical parametric chirped-pulse amplification (OPCPA). Whilst providing adequate peak power to trigger high-harmonic generation (HHG) in an argon gas jet, our new Yb-based laser source permits enhanced signal-to-noise ratio, finer energy resolution, and shorter data acquisition times in pump-probe photoemission studies of solid samples [1].<br/>Time- and angle-resolved photoemission spectroscopy (TR-ARPES) has brought new insights into challenging aspects of surface science [2]. Advancements in light sources have improved pulse compression to gain higher time resolution, better spatial resolution, and enhanced signal-to-noise ratio. These improvements, however, lead to vacuum space-charge effects, which compromise energy and momentum resolution and generate peak shifts [3]. To minimize these issues and improve the data collection rate during pump-probe experiments, it is necessary to increase the laser repetition rate.<br/>Our TR-ARPES beamline consists of a Fastlite OPCPA, pumped by a 220-W regenerative amplifier. Post-compression, the OPCPA delivers 50 – 100 fs pulses in the ranges of 1450 – 1850 nm (signal) and 2350 – 3680 nm (idler), with up to 200 µJ of energy per pulse at 100-kHz repetition rate.<br/>HHG is achieved by focusing the signal beam into an argon cell, either directly or following SHG. When driven by the second harmonic of the signal, the HHG output spans energies from 20 to 45 eV, with a maximum flux of ~1010 photons/second at the sample.<br/>The XUV beamline includes a monochromator select probe photon energies. A demagnification unit focusses the XUV spot to 20 µm at the sample, facilitating measurements on small samples and on individual structural domains within inhomogeneous samples. The experimental endstation is equipped with a hemispherical analyzer, and a newly commissioned “Fermi Surface Mapper” analyzer [4], which permits photoelectron momentum mapping sliced in the energy axis [5].<br/>To expand the horizon of experiments, we have recently secured funding for a £17M major upgrade [6] of all the CLF’s ultrafast facilities. Our main goal at Artemis is to increase the repetition rate available for atomic molecular, and optical (AMO) science—which, at present, is still running on our older 1-kHz titanium sapphire laser system—and to take advantage of improved data collection rates, by upgrading the endstations on both the TR-ARPES and AMO beamlines. The upgrade will include the following:<br/>1) TR-ARPES endstation incorporating both a momentum microscope and a hemispherical analyzer.<br/>2) 100-kHz Yb-based laser system, with 1.5-mJ, &lt;50-fs pulses at 1 μm for HHG, and tunable &lt;50-fs pulses from 235 nm to 10 µm.<br/>3) AMO endstation offering a dual-coincidence electron-ion spectrometer, laser-desorption, and supersonic gas-jet sources.<br/><br/><u>References</u><br/>1) N Thiré, et al., Sci. Rep. 13, 18874 (2023).<br/>2) C. J. Sayers, et al., Phys. Rev. Lett. 130, 156401 (2023).<br/>3) G. Schönhense, et al., Rev. Sci. Instrum. 92, 053703 (2021).<br/>https://fermiologics.com/products/fesuma/<br/>4) P. Majchrzak, et al., arXiv:2309.11535v1 [cond-mat. mtrl-sci]<br/>https://www.clf.stfc.ac.uk/Pages/HiLUX.aspx