Generation of period-tunable MeV few-attosecond electron pulse trains via counter-propagating lasers

Abstract

Attosecond electron pulses permit real-time probing of ultrafast material dynamics. However, generating few-attosecond electron pulses with MeV energies and low energy spread remains an enduring challenge for conventional beam-modulation techniques. Here we propose a compact dual-laser scheme to modulate readily accessible electron beams into few-attosecond pulse trains, leveraging a stable parametric-resonance regime coupled with direct laser acceleration. An accompanying theoretical framework is developed, yielding closed-form expressions for the tunable pulse period, duration, energy modulation and formation time, enabling flexible customization of the produced attosecond pulse trains. Consistent with these theoretical predictions, simulations verify the generation of ~ 1 as pulses with a Lorentz factor up to 15 and a relative energy spread below 0.02%. This work offers an experimentally feasible pathway toward high-quality, tunable MeV few-attosecond electron pulses.