Injection and Acceleration of Electrons by Radially Polarized Laser Pulses in a Plasma Channel

Abstract

We consider injection and subsequent acceleration of electrons in narrow plasma channels irradiated by linearly and radially polarized ultraintense laser pulses. Using three-dimensional particle-in-cell simulations, we show that radially polarized beams significantly promote electron release from the channel walls and lead to enhanced injection. We compare an f/10 linearly polarized laser beam with two radially polarized cases: one focused more tightly (f/5) to match peak intensity, and one at equal f/10 to capture polarization effects. The radially polarized f/10 case injects approximately one-third more charge than the linearly polarized case, while the f/5 radially polarized case outperforms the linearly polarized one by about a factor of two in terms of maximum electron energy. These results highlight polarization and focusing geometry as key parameters for optimizing laser-driven electron acceleration setups.

Figures (4)

• Figure 1: Setup of the PIC simulation for the RP $\mathrm{f}/5$ configuration. The laser pulse (orange) propagates inside a preformed narrow plasma channel (gray). The radial electron density of the channel is shown in the figure by $n_{e}(r)$. An aspect ratio of $1\!:\!4 \; (\text{x-axis} : \text{r-axis})$ is applied in the figure.
• Figure 2: Left: Angular and energy spectral distribution of electrons at the end of the simulation, for the three laser configurations: (a) LP $\mathrm{f}/10$, (b) RP $\mathrm{f}/10$, and (c) RP $\mathrm{f}/5$. High-energy electrons exhibit narrower divergence, where for the RP $\mathrm{f}/5$ case a distinct narrow electron population of energy $\gtrapprox 1 \, \mathrm{GeV}$ overlaps to the broader distribution of the moderate-to-low energy electrons. Right: Angular electron energy flux for (a) LP $\mathrm{f}/10$, (b) RP $\mathrm{f}/10$, and (c) RP $\mathrm{f}/5$ (black line). Red, green and blue curves represent energy ranges $\mathcal{E} > 1 \, \mathrm{GeV}$, $0.1 < \mathcal{E}< 1 \, \mathrm{GeV}$, and $\mathcal{E} < 0.1 \, \mathrm{GeV}$, respectively. The $\mathrm{f}/5$ RP case is the only one that forms a peak for electron energies $> 1 \, \mathrm{GeV}$ and a charge threshold $> 0.1 \, \mathrm{nC}$.
• Figure 3: Temporal evolution of maximum electron energy for the three laser configurations. RP $\mathrm{f}/5$ continues accelerating electrons up to $600 \, \mathrm{fs}$, reaching nearly $2 \, \mathrm{GeV}$, while both the LP $\mathrm{f}/10$ and RP $\mathrm{f}/10$ saturate near $1.2 \, \mathrm{GeV}$.
• Figure 4: Longitudinal profile of current for core electrons ($r < 9 \,\mathrm{\upmu m}$, cyan) and sheath electrons ($r > 9 \,\mathrm{\upmu m}$, mustard) for the (a) LP $\mathrm{f}/10$, (b) RP $\mathrm{f}/10$, and (c) RP $\mathrm{f}/5$ case. RP $\mathrm{f}/10$ carries the largest total charge in both the core and sheath regions, and spreads across an extended tail. Integrated charges for each region are indicated in the legend. (d) Radial profile of the current density for the RP $\mathrm{f}/5$ case, for electrons with $250 \, \mathrm{\upmu m} < x < 260 \, \mathrm{\upmu m}$ (peak current).