Journal
JOURNAL OF SYNCHROTRON RADIATION
Volume 28, Issue -, Pages 1891-1908Publisher
INT UNION CRYSTALLOGRAPHY
DOI: 10.1107/S1600577521010511
Keywords
time-of-flight spectroscopy; momentum microscopy; ARPES; photoelectron diffraction; pulse picking
Categories
Funding
- BMBF [05K16UMB, 05K19UM1]
- Deutsche Forschungsgemeinschaft DFG (German Research Foundation) [TRR 173-268565370, TRR 288-422213477]
- Projekt DEAL
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This article presents two techniques for efficient time-of-flight recording at sources with high repetition rates, including a fast electron-optical beam blanking unit and a bandpass pre-filter, enabling efficient photoelectron spectroscopy and momentum microscopy at synchrotron sources, lasers, and cavity-enhanced high-harmonic sources operating at 100-500MHz.
The small time gaps of synchrotron radiation in conventional multi-bunch mode (100-500MHz) or laser-based sources with high pulse rate (similar to 80MHz) are prohibitive for time-of-flight (ToF) based photoelectron spectroscopy. Detectors with time resolution in the 100ps range yield only 20-100 resolved time slices within the small time 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 electron-optical 'pulse-picking' with any desired repetition period. Aberration-free momentum distributions have been recorded at reduced pulse periods of 5MHz (at MAXII) and 1.25MHz (at BESSYII). The approach is compared with two alternative solutions: a bandpass pre-filter (here a hemispherical analyzer) or a parasitic four-bunch island-orbit pulse train, coexisting with the multi-bunch pattern on the main orbit. Chopping in the time domain or bandpass pre-selection in the energy domain can both enable efficient ToF spectroscopy and photoelectron momentum microscopy at 100-500MHz synchrotrons, highly repetitive lasers or cavity-enhanced high-harmonic sources. The high photon flux of a UV-laser (80MHz, <1meV bandwidth) facilitates momentum microscopy with an energy resolution of 4.2meV and an analyzed region-of-interest (ROI) down to <800nm. In this novel approach to `sub-mu m-ARPES' the ROI is defined by a small field aperture in an intermediate Gaussian image, regardless of the size of the photon spot.
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