Terahertz-optical intensity grating for creating high-charge, attosecond electron bunches

Jeremy Lim,Yidong Chong,Liang Jie Wong

doi:10.1088/1367-2630/ab0aa7

Abstract

Ultrashort electron bunches are useful for applications like ultrafast imaging, coherent radiation production, and the design of compact electron accelerators. Currently, however, the shortest achievable bunches, at attosecond time scales, have only been realized in the single- or very few-electron regimes, limited by Coulomb repulsion and electron energy spread. Using ab initio simulations and complementary theoretical analysis, we show that highly-charged bunches are achievable by subjecting relativistic (few MeV-scale) electrons to a superposition of terahertz and optical pulses. We provide two detailed examples that use realistic electron bunches and laser pulse parameters which are within the reach of current compact set-ups: one with bunches of >240 electrons contained within 20 as durations and 15 μm radii, and one with final electron bunches of 1 fC contained within sub-400 as durations and 8 μm radii. Our results reveal a route to achieve such extreme combinations of high charge and attosecond pulse durations with existing technology.

Highlights

Electron bunches of femtosecond-to-attosecond-scale duration are useful tools for studying ultrafast atomicscale processes, including structural phase transitions in condensed matter [1,2,3,4,5,6], sub-cycle changes in oscillating electromagnetic waveforms [7], and the dynamics of biological structures [8, 9]
We presented a scheme in which counter-propagating terahertz and optical pulses are used to compress relativistic electrons into a train of attosecond-duration bunches
Our ab initio simulations take nearand far-field space charge effects into account, and use exact, non-paraxial pulse profiles to model single-cycle, tightly-focused terahertz pulses; this is a significant advance over previous numerical studies of similar intensity grating compression schemes, which assumed non-interacting electrons and planar or paraxial electromagnetic waves

Summary

Introduction

Electron bunches of femtosecond-to-attosecond-scale duration are useful tools for studying ultrafast atomicscale processes, including structural phase transitions in condensed matter [1,2,3,4,5,6], sub-cycle changes in oscillating electromagnetic waveforms [7], and the dynamics of biological structures [8, 9]. Existing schemes for electron bunch compression include the use of electrostatic elements [17], time-varying fields within radio-frequency (RF) cavities [18,19,20,21,22], electromagnetic transients [23,24,25,26,27,28,29,30], and a combination of optical laser pulses and dielectric membranes [10] In all of these schemes, space charge effects and velocity spread enforce a tradeoff between electron bunch charge and pulse duration. The shortest electron bunches produced to date lie in the single-electron regime, with durations of 655 as [26] and 820 as [10], and indirect measurements indicating durations as short as 260 as [28]

Results

Discussion

Conclusion