Femtosecond Probing of Plasma Wakefields and Observation of the Plasma Wake Reversal Using a Relativistic Electron Bunch

Abstract

Relativistic wakes produced by intense laser or particle beams propagating through plasmas are being considered as accelerators 1, 2 for next generation of colliders and coherent light sources 3 . Such wakes have been shown to accelerate electrons and positrons to several gigaelectronvolts (GeV) 4-10 , with a few percent energy spread 8-10 and a high wake-to-beam energy transfer efficiency 7 . However, complete mapping of electric field structure of the wakes has proven elusive. Here we show that a high-energy electron bunch can be used to probe the fields of such light-speed wakes with femtosecond resolution. The highly transient, microscopic wakefield is reconstructed from the density modulated ultra-short probe bunch

Probing ultrafast magnetic-field generation by current filamentation instability in femtosecond relativistic laser-matter interactions

“…In situ measurements of the magnetic-field fluctuations at the irradiated target surface have been performed using optical polarimetry [39,40], yet this technique cannot access the volumetric distribution of the fields, and the data obtained so far could not capture their femtosecond timescale dynamics. Probing plasma electromagnetic fields by an ultrashort electron beam was previously exploited to image plasma wakefields in a laser wakefield accelerator (LWFA) [41] or large-scale inductively generated magnetic fields in target normal sheath acceleration [42].…”

High-resolution sampling of beam-driven plasma wakefields

“…However, a direct measurement of the electric fields requires the use of charged particles. This can be done by traversing the wake perpendicular to its direction of motion with a short probe electron bunch, such that the transversely-integrated wakefield is imprinted on the transverse profile of the probe 18 . Alternatively, in a beam-driven plasma accelerator the beam itself can be used to measure the longitudinal wakefield, by comparing the longitudinal phase space (i.e., a time-resolved energy spectrum) of bunches with and without plasma interaction.…”

Faraday rotation study of plasma bubbles in GeV wakefield accelerators

“…One can recover optical contrast by using mid-IR probe pulses that maintain equivalent n e /n (pr) cr , but the advantage of higher feature resolution is then lost. 10 Alternatively, Zhang et al 20 used fs e-bunches from a separate "diagnostic" LPA to probe internal structure of laser-induced wakes in plasma of n e as low as 3 × 10 17 cm −3 . However, the detected plasma wave was in the linear, rather than bubble, regime.…”