Abstract
A frontier challenge in implementing femtosecond electron microscopy is to gain precise optical control of intense beams to mitigate collective space charge effects for significantly improving the throughput. Here, we explore the flexible uses of an RF cavity as a longitudinal lens in a high-intensity beam column for condensing the electron beams both temporally and spectrally, relevant to the design of ultrafast electron microscopy. Through the introduction of a novel atomic grating approach for characterization of electron bunch phase space and control optics, we elucidate the principles for predicting and controlling the phase space dynamics to reach optimal compressions at various electron densities and generating conditions. We provide strategies to identify high-brightness modes, achieving ∼100 fs and ∼1 eV resolutions with 106 electrons per bunch, and establish the scaling of performance for different bunch charges. These results benchmark the sensitivity and resolution from the fundamental beam brightness perspective and also validate the adaptive optics concept to enable delicate control of the density-dependent phase space structures to optimize the performance, including delivering ultrashort, monochromatic, high-dose, or coherent electron bunches.
Highlights
INTRODUCTIONRadio-frequency (RF) cavities, for electron bunch compression
Electrons possess the highest scattering cross-section1 that could enable the development of high-performance beamlines,2 including the delivery of ultrashort electron bunches for broad ranges of ultrafast science investigation at a very high throughput
We explore the flexible uses of an RF cavity as a longitudinal lens in a high-intensity beam column for condensing the electron beams both temporally and spectrally, relevant to the design of ultrafast electron microscopy
Summary
Radio-frequency (RF) cavities, for electron bunch compression This latest development is especially attractive for the future UEM design where the high-intensity implementation with longitudinal optics would be crucial to enable research on the irreversible processes, longlived metastable phases, and for elucidating the transient bonding through ultrafast core-level spectroscopy.. An impediment that has prevented rapid advances in designing high-intensity UEM systems is the paucity of experimental data available on efficiently handling the spacecharge-dominated beams This is despite the recent success in implementing time-compression UED systems, where the main focus is to accomplish velocity bunching through an RF cavity. The advances discussed here include: the deployment of the atomic grating approach and theoretical models for characterizing phase space structures of the electron bunches; an understanding of the density-dependent bunch phase space structure evolution; control of bunch phase space through the RF cavity as a longitudinal lens; identification of high-brightness modes; and elucidation of the nonlinear effects induced at beam crossovers.
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