Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

The longitudinal profile of ultra-short electron bunches from Laser wakefield accelerators (LWFA) intricately depends on the ultrafast injection dynamics and laser-electron beam interaction during acceleration. Detailed knowledge of these electron bunch temporal profile is critical for the design of future table-top x-ray light-sources, as well as for the characterization of ultrashort electron beam probes or THz sources.

We present experimental results based on spectral single-shot measurements of broadband coherent transition radiation (UV to mid-IR, 250nm-11.35μm) from LWFA electron bunches passing through a metal foil. In particular, we examine different LWFA injection mechanisms, such as self-truncated ionization-injection, density-shock-assisted injection and self-injection. By analyzing the transition radiation spectra, we reconstruct electron bunch profiles including sensitivity and uniqueness properties. The electron bunch profiles of the respective injection regimes show a broad range of bunch durations, while individual shots feature complex longitudinal electron pulse profiles that stretch accross several time scales, covering the bunch envelope, its microstructures to below sub-µm, both on top of temporally more extended charge-pedestals and tails. Based on hundreds of LWFA shots, we present systematic statistics and correlations on bunch duration, peak currents with respect to electron injection-method, gas-density, as well as bunch energy, energy spread and charge.