A quantitative comparison of time-of-flight momentum microscopes and hemispherical analyzers for time- and angle-resolved photoemission spectroscopy experiments

Abstract

Time-of-flight-based momentum microscopy has a growing presence in photoemission studies, as it enables parallel energy- and momentum-resolved acquisition of the full photoelectron distribution. Here, we report table-top extreme ultraviolet time- and angle-resolved photoemission spectroscopy (trARPES) featuring both a hemispherical analyzer and a momentum microscope within the same setup. We present a systematic comparison of the two detection schemes and quantify experimentally relevant parameters, including pump- and probe-induced space-charge effects, detection efficiency, photoelectron count rates, and depth of focus. We highlight the advantages and limitations of both instruments based on exemplary trARPES measurements of bulk WSe2. Our analysis demonstrates the complementary nature of the two spectrometers for time-resolved ARPES experiments. Their combination in a single experimental apparatus allows us to address a broad range of scientific questions with trARPES.

Unveiling the orbital texture of 1T-TiTe2 using intrinsic linear dichroism in multidimensional photoemission spectroscopy

“…One additional route that we envision is the ultrafast timeresolved investigation of dynamical modification of orbital texture upon impulsive photoexcitation of solids. Angle-resolved photoemission spectroscopy in general, and more specifically the experimental setup used in this study, is compatible with timeresolved studies with femtosecond temporal resolution 40,42,60 . Thus, combining this differential observable with pump-probe schemes could allow following in real-time modification of orbital texture during non-equilibrium topological phase transitions 61,62 , photoinduced orbital order 63 and coherent phonon excitation breaking fundamental symmetries of the materials 64 .…”

“…One of the major advantages of this type of detector is the parallel detection of the 3D photoemission intensity I(E, k x , k y ) in a single measurement, without having to rotate the sample in the laboratory frame 41 . More details about the experimental setup can be found elsewhere 40,42 and in the "Methods" section. Giving the energydependence of the inelastic mean free path of the outgoing electrons 43,44 , working in the XUV spectral range ensure that most of the detected electrons are coming from the topmost 1T-TiTe 2 layer (first atomic trilayer) 24 .…”

Ultrafast dynamical Lifshitz transition

“…We call this technique time-resolved multidimensional photoemission spectroscopy since we directly measure 4D photoemission intensity I(E B , k x , k y , Δt), instead of the more standard 3D photoemission intensity I(E B , k ‖ , Δt), when using hemispherical analyzer. More information about the experimental setup can be found in Materials and Methods and in (27).…”

Direct measurement of key exciton properties: Energy, dynamics, and spatial distribution of the wave function

“…Figure 1a depicts the experimental scheme of trARPES employing femtosecond near-infrared pump and extreme ultraviolet (XUV) probe pulses combined with two types of photoelectron analyzers: a hemispherical analyzer (HA) and a time-of-flight momentum microscope (MM). The whole setup allows us to measure the threedimensional (3D) time-dependent electronic structure in a given energy-momentum-plane with high counting statistics using the HA, and alternatively resolve both in-plane momentum directions yielding a four-dimensional (4D) photoemission signal I(E kin , k x , k y , t) of the entire valence band with the MM [21,25]. Figure 1b-d and e-g show snapshots of the 3D and 4D data with 1.55 eV excitation, respectively, at three selected time delays: (i) prior to optical excitation, showing the ground-state band structure of WSe 2 from the Brillouin zone (BZ) center Γ (only shown in the MM data) to the BZ boundary K points (b and e); (ii) upon optical excitation resonant with the A exciton absorption (the first excitonic state), featuring excited-state signal at the K and Σ valleys (c and f); and (iii) at t = 100 fs after optical excitation, with excited-state signal mostly at the Σ valleys (d and g).…”