Improving electron dephasing of an all-optical multi-GeV laser wakefield accelerator

Laser plasma accelerators can generate acceleration gradients of 10~100 GeV/m and have delivered multi-GeV electron beams. In a recent experiment, we demonstrated electron acceleration up to 5 GeV in a 20-cm plasma waveguide, formed via self-waveguiding pulses in a low density hydrogen gas jet [1,2]. The long optical guiding of multi-100 TW pulses causes complex evolution of the laser driver envelope and spectrum, which entails further study to improve the accelerated electron bunch quality. In this work we investigate both numerically and experimentally the additional dephasing due to pump depletion during laser propagation in a plasma waveguide. We propose and present two potential ways to alleviate this effect by either controlling the laser driver chirp or using shorter wavelength driver, such as its second harmonic. Finally, we present numerical simulations and electron energy spectra validating the proposed methods.

[1] B. Miao et al., Multi-GeV electron bunches from an all-optical laser wakefield accelerator, arXiv:2112.03489 (2021).

[2] L. Feder et al., Self-waveguiding of relativistic laser pulses in neutral gas channels, Phys. Rev. Res. 2, 043173 (2020).