Efficient electron injection by hybrid parametric instability and forward direct laser acceleration in subcritical plasma

Abstract

The efficient injection of electrons into a propagating relativistic laser pulse with normalized vector potential a 0 ∼ 2 is demonstrated numerically and experimentally in a thin plasma layer with density 0.15–0.3 of the critical value. The injection is due to the wavebreaking of parametric plasma waves. The trapped particles gain multi-MeV (up to 20 MeV) energies by the direct laser acceleration in the plasma channel formed by the laser pulse in the lower density plasma tail. Numerical calculations were supported by experiments with micron-scale films pre-evaporated by an additional nanosecond laser pulse and a TW femtosecond laser facility. The experimentally observed bunch of electrons with energy above 1.6 MeV had a divergence of ∼0.05 rad and charge of ∼50 pC measured with photoneutron Be(g,n) reaction.

Phase space consideration of low energy electron injection for Direct Laser Acceleration

“…6). Let us note, that these electron density values lie between that commonly used in both DLA and LWFA acceleration: tenths of n cr for the DLA [7] and thousandths of n cr for the LWFA. However, the required electron density can be experimentally achieved, for example, using high-density gas jet.…”

“…While the LWFA with 1 PW laser has been shown to produce high-quality quasi-monochromatic electron bunches with energies up to 8 GeV [4], a divergence of 0.2 mrad and charge of several hundred pC, the DLA usually yields the quasiexponential energy spectrum, but much higher charges (up to hundreds of nC [5]). It is also can be implemented on tabletop femtosecond laser systems with 1-10 TW peak power [6,7].…”

Optimized laser-assisted electron injection into a quasi-linear plasma wakefield

“…The laser-plasma interaction in the injection scheme discussed above could be optimized further following the recent experimental findings [18]. This is the subject of on-going work.…”

Transition radiation in the THz range generated in the relativistic laser—tape target interaction

“…For ∆t fs−ns = −2 and −1 ns, which correspond to the electrons' signal maximum, an electron beam with ∼0.05 rad divergence (D) is observed. Its properties were previously discussed in detail in [20,21], here we only note its ∼0.2 rad pointing stability (PS) over 500 consecutive laser shots and temperature T ≈ 2 MeV (parameter of exponential electrons' energy distribution dN/dE ∼ e −E/T , typical for laser-plasma accelerators, where N-electrons' number, E-electrons' energy). For ∆t fs−ns = 0 ns beam divergence increases to D = 0.1-0.2 rad and its pointing stability up to PS ∼ 0.4 rad, while temperature decreases to T ≈ 1.5 MeV.…”

“…In our previous papers, an electrons' acceleration from such a two-pulse scheme had already been experimentally and numerically studied [20,21]. The first results on the generation of THz radiation on our experimental setup were also published in [21], where a strong dependence of the THz radiation energy on the delay between the main pulse and the prepulse (i.e.…”