Electron beam polarization in the bubble regime of the interaction between a high-intensity laser and a longitudinally pre-polarized plasma is investigated by means of the Thomas-Bargmann-Michel-Telegdi equation. Using a test-particle model, the dependence of the accelerated electron polarization on the bubble geometry is analyzed in detail. Tracking the polarization dynamics of individual electrons reveals that although the spin direction changes during both the self-injection process and acceleration phase, the former has the biggest impact. For nearly spherical bubbles, the polarization of electron beam persists after capture and acceleration in the bubble. By contrast, for aspherical bubble shapes, the electron beam becomes rapidly depolarized, and the net polarization direction can even reverse in the case of a oblate spheroidal bubble. These findings are confirmed via particle-in-cell simulations.

In this paper, we studied the characteristics of radiation emitted by electrons accelerated in a laser–plasma interaction by using the Lienard–Wiechert field. In the interaction of a laser pulse with a underdense plasma, electrons are accelerated by two mechanisms: direct laser acceleration (DLA) and laser wakefield acceleration (LWFA). At the beginning of the process, the DLA electrons emit most of the radiation, and the DLA electrons emit a much higher peak photon energy than the LWFA electrons. As the laser–plasma interaction progresses, the LWFA electrons become the major radiation emitter; however, even at this stage, the contribution from DLA electrons is significant, especially to the peak photon energy.

It is known that high quality proton beams can be produced in the radiation pressure acceleration (RPA) by using a circularly polarized ultraintense super-Gaussian laser. However, a transverse mismatching phenomenon between the laser intensity profile and the particle spatial distribution appears in the later stage of RPA, which leads to a decompression of proton beam and broadening of the energy spectrum. To weaken this effect, a new scheme with an additional plasma channel located behind a thin hydrogen foil is proposed. It is found that a good local matching can be maintained when the laser pulse propagates in the channel, which contributes to a stable RPA for a longer time. Two-dimensional particle-in-cell simulations show that the proton beam has a peak energy of 2.0 GeV and energy spread of 13.8% at t ¼ 300 fs. With further acceleration until t ¼ 500 fs, a better quality beam with about 40% increase in peak energy and 26.2% improvement in energy conversion efficiency for high-energy protons (≥1.5 GeV) can be obtained finally. Meanwhile, the energy spread drops from 100% to 28.5%. This work may provide a more promising way to generate the high quality proton beam.