Schönhense G, Medjanik K, Fedchenko O, Zymaková A, Chernov S, Kutnyakhov D, Vasilyev D, Babenkov S, Elmers H J, Baumgärtel P, Goslawski P, Öhrwall G, Grunske T, Kauerhof T, von Volkmann K, Kallmayer M, Ellguth M, Oelsner A
Institut für Physik, Johannes Gutenberg Universität, 55128 Mainz, Germany.
BESSY II, Helmholtz-Zentrum, 12489 Berlin, Germany.
J Synchrotron Radiat. 2021 Nov 1;28(Pt 6):1891-1908. doi: 10.1107/S1600577521010511. Epub 2021 Nov 3.
The small time gaps of synchrotron radiation in conventional multi-bunch mode (100-500 MHz) or laser-based sources with high pulse rate (∼80 MHz) are prohibitive for time-of-flight (ToF) based photoelectron spectroscopy. Detectors with time resolution in the 100 ps 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 5 MHz (at MAX II) and 1.25 MHz (at BESSY II). 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 100-500 MHz synchrotrons, highly repetitive lasers or cavity-enhanced high-harmonic sources. The high photon flux of a UV-laser (80 MHz, <1 meV bandwidth) facilitates momentum microscopy with an energy resolution of 4.2 meV and an analyzed region-of-interest (ROI) down to <800 nm. In this novel approach to sub-µm-ARPES' the ROI is defined by a small field aperture in an intermediate Gaussian image, regardless of the size of the photon spot.
在传统的多束团模式（100 - 500 MHz）下，同步辐射的小时间间隔，或者具有高脉冲频率（约80 MHz）的基于激光的光源的小时间间隔，对于基于飞行时间（ToF）的光电子能谱来说是不利的。具有100 ps范围时间分辨率的探测器在小时间间隔内只能产生20 - 100个分辨的时间切片。在这里，我们展示了两种在高重复率光源下实现高效ToF记录的技术。集成在光电子动量显微镜中的具有GHz带宽的快速电子光学束消隐单元，允许以任何所需的重复周期进行电子光学“脉冲选择”。在5 MHz（在MAX II）和1.25 MHz（在BESSY II）的降低脉冲周期下记录了无像差的动量分布。该方法与两种替代解决方案进行了比较：带通预滤波器（这里是半球形分析仪）或与主轨道上的多束团模式共存的寄生四束团岛轨道脉冲序列。在时域中的斩波或在能量域中的带通预选择都可以在100 - 500 MHz同步加速器、高重复率激光器或腔增强高谐波源上实现高效的ToF光谱学和光电子动量显微镜。紫外激光（80 MHz，<1 meV带宽）的高光子通量有助于实现能量分辨率为4.2 meV且分析感兴趣区域（ROI）低至<800 nm的动量显微镜。在这种“亚微米角分辨光电子能谱”的新方法中，ROI由中间高斯图像中的小场孔径定义，而与光子光斑的大小无关。
