Extreme ultraviolet time- and angle-resolved photoemission setup with 21.5 meV resolution using high-order harmonic generation from a turn-key Yb:KGW amplifier

Abstract

Characterizing and controlling electronic properties of quantum materials require direct measurements of nonequilibrium electronic band structures over large regions of momentum space. Here, we demonstrate an experimental apparatus for time-and angle-resolved photoemission spectroscopy using high-order harmonic probe pulses generated by a robust, moderately high power (20 W) Yb:KGW amplifier with a tunable repetition rate between 50 and 150 kHz. By driving high-order harmonic generation (HHG) with the second harmonic of the fundamental 1025 nm laser pulses, we show that single-harmonic probe pulses at 21.8 eV photon energy can be effectively isolated without the use of a monochromator. The on-target photon flux can reach 5 × 10 10 photons/s at 50 kHz, and the time resolution is measured to be 320 fs. The relatively long pulse duration of the Yb-driven HHG source allows us to reach an excellent energy resolution of 21.5 meV, which is achieved by suppressing the space-charge broadening using a low photon flux of 1.5 × 10 8 photons/s at a higher repetition rate of 150 kHz. The capabilities of the setup are demonstrated through measurements in the topological semimetal ZrSiS and the topological insulator Sb 2−x GdxTe 3 .

High harmonic generation and application for photoemission spectroscopy in condensed matter

“…Liu et al proposed to take advantage of a long pulse duration and short wavelength laser to generate directly the narrowband individual harmonic, to avoid the use of a monochromator. The increased photon efficiency and tuneable repetition rate of up to 150 kHz enabled an energy resolution of 21.5 meV [90]. Another advantage of the lack of a monochromator is the flexibility to conduct attosecond photoionization time delay measurement in a material similar to that in atoms and molecules.…”

Multispectral time-resolved energy-momentum microscopy using high-harmonic extreme ultraviolet radiation

“…Over the past fifteen years, trARPES has evolved into a powerful ARPES modality providing direct dynamical information on electronic structure at the fundamental time scales of electronic and atomic motion, particularly on photoinduced transient changes of electronic states and their population. [23][24][25][26][27][28][29][30][31][32] trARPES is now routinely performed using table-top laser sources based on fourth and higher harmonic generation (HHG) in solids 33,34 and gases [35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50] , respectively, as well as using free-electron lasers (FELs) based on the self-amplification of spontaneous emission (SASE) of free electrons in undulators. 21 The corresponding probe photon energies in trARPES range from the far UV to soft x-rays where a sweet spot currently is the intermediate extreme ultraviolet (XUV) regime.…”

“…In the XUV, HHG-based trARPES can optionally provide high time, energy, and momentum resolution in conjunction with kHz-to-MHz repetition rates and a sufficiently wide detection window of the surface-parallel momentum (k x , k y ) to fully cover typical Brillouin-zone (BZ) dimensions. [35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50] Moreover, HHG sources combined with monochromators enable multispectral measurements as they can deliver a useable, discretely tunable photon-energy range of ≈8-40 eV. 35,36,40,43,44,46 However, this multispectral capability has so far rarely been exploited in trARPES experiments, and recently several setups for HHG-based trARPES have even been optimized for operation at one specific photon energy only.…”

Ultrafast relaxation of acoustic and optical phonons in a topological nodal-line semimetal ZrSiS

“…A schematic illustration of the geometry of our tr-ARPES experiment is shown in Fig. 1(a) and the details of the experimental setup is given in the reference [46].…”