Moriová Kamila, Koutenský Petr, Chirita-Mihaila Marius-Constantin, Kozák Martin
Department of Chemical Physics and Optics, Faculty of Mathematics and Physics, Charles University, Ke Karlovu 3, 12116 Prague 2, Czech Republic.
Rev Sci Instrum. 2025 Jun 1;96(6). doi: 10.1063/5.0258415.
In this work, we present the implementation of an all-optical method for directly measuring electron pulse duration in an ultrafast scanning electron microscope. Our approach is based on the interaction of electrons with the ponderomotive potential of an optical standing wave and provides a precise in situ technique to characterize femtosecond electron pulses at the interaction region across a wide range of electron energies (1-30 keV). By using single-photon photoemission of electrons by ultraviolet femtosecond laser pulses from a Schottky emitter, we achieve electron pulse durations ranging from 0.5 ps at 30 keV to 2.7 ps at 5.5 keV under optimal conditions where Coulomb interactions are negligible. In addition, we demonstrate that reducing the photon energy of the femtosecond pulses used for photoemission from 4.8 eV (257.5 nm) to 2.4 eV (515 nm) decreases the initial energy spread of emitted electrons, leading to significantly shorter pulse durations, particularly at lower electron energies.
在这项工作中，我们展示了一种全光学方法的实现，用于在超快扫描电子显微镜中直接测量电子脉冲持续时间。我们的方法基于电子与光学驻波的有质动力势的相互作用，并提供了一种精确的原位技术，以在很宽的电子能量范围（1 - 30 keV）内表征相互作用区域的飞秒电子脉冲。通过使用来自肖特基发射极的紫外飞秒激光脉冲对电子进行单光子光发射，在库仑相互作用可忽略不计的最佳条件下，我们实现了电子脉冲持续时间从30 keV时的0.5 ps到5.5 keV时的2.7 ps。此外，我们证明将用于光发射的飞秒脉冲的光子能量从4.8 eV（257.5 nm）降低到2.4 eV（515 nm）会降低发射电子的初始能量展宽，从而导致脉冲持续时间显著缩短，特别是在较低电子能量时。
