Time-of-Flight Photoelectron Momentum Microscopy at 100-500 MHz Synchrotron Sources: Electron-Optical Chopping or Bandwidth Pre-Selection

G. Schoenhense; K. Medjanik; O. Fedchenko; A. Zymakova; S. Chernov; D. Vasilyev; S. Babenkov; H. J. Elmers; P. Baumgärtel; P. Goslawski; G. Oehrwall; M. Ellguth; A. Oelsner

arXiv · 2105.00317

Time-of-Flight Photoelectron Momentum Microscopy at 100-500 MHz Synchrotron Sources: Electron-Optical Chopping or Bandwidth Pre-Selection

G. Schoenhense·K. Medjanik·O. Fedchenko·A. Zymakova·S. Chernov·D. Vasilyev·S. Babenkov·H. J. Elmers·P. Baumgärtel·P. Goslawski·G. Oehrwall·M. Ellguth·A. Oelsner

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Abstract

The small time gap of synchrotron radiation in conventional multi-bunch mode (100-500MHz) is prohibitive for time-of-flight (ToF) based electron spectroscopy. Even the new generation of delay-line detectors with improved time resolution (<100ps) yields only 20-100 resolved time slices within a 2-10ns gap. Here we present two techniques of implementing efficient ToF recording at sources with high repetition rate. A fast electron-optical beam blanking unit with GHz bandwidth, integrated in a photoelectron momentum microscope, allows chopping the photon-pulse train to any desired repetition period. Aberration-free momentum distributions have been recorded at chopped pulse periods of 5MHz (at MAX II) and 1.25MHz (at BESSY II). The approach is benchmarked against the alternative way of implementing a dispersive element, e.g. a hemispherical analyzer, in the electron optics. Both approaches, chopping in the time domain as well as bandpass pre-selection in the energy domain, can enable efficient ToF spectroscopy, spectroscopic real-space imaging and momentum microscopy with few-meV resolution using 100-500MHz Synchrotron radiation, highly-repetitive lasers or cavity-enhanced high-harmonic sources. For comparison, we show results recorded at BESSY II with a parasitic 4-bunch island-orbit pulse train, coexisting with the 500MHz filling pattern on the main orbit.

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G. Schoenhense, K. Medjanik, O. Fedchenko, A. Zymakova, S. Chernov, D. Vasilyev, S. Babenkov, H. J. Elmers, P. Baumgärtel, P. Goslawski, G. Oehrwall, M. Ellguth, A. Oelsner. 2021-05-01. Time-of-Flight Photoelectron Momentum Microscopy at 100-500 MHz Synchrotron Sources: Electron-Optical Chopping or Bandwidth Pre-Selection. https://arxiv.org/abs/2105.00317

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