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

Ultrashort electron bunches are useful for applications like ultrafast imaging, coherent radiation production, and compact sources of accelerated electrons. Currently, however, the shortest achievable bunches, at attosecond time scales, have only been realized in the single or very few electron regime, limited by Coulomb repulsion and electron energy spread. We will present ab initio simulation results and theoretical analysis which show that highly-charged bunches are achievable by subjecting moderately-relativistic (few MeV-scale) electrons to a superposition of terahertz and optical pulses. Using realistic electron bunches and laser pulse parameters which are within the reach of current compact setups, we provide two detailed examples: one with final bunches of ~1 fC contained within sub-400 as durations and 8 micron radii, and one with bunches of > 25 electrons contained within 20 as durations and 15 micron radii. Our results reveal a route to achieve such extreme combinations of high charge and attosecond pulse durations with existing technology.