Electron transport in a nanowire irradiated by an intense laser pulse

Electron transport in a nanowire exhibits a distinct behavior following the irradiation of intense laser pulse. Using particle-in-cell simulation, we observe a large-amplitude particle-driven wakefield excitation followed by electron acceleration in the solid density. Besides, we observed the quiver of the electrons across the nanowire under the action of the surrounding laser electric field facilitating deeper wakefield propagation in the nanowire with $2.5\times$ energy gain over a flat target. These results open insights into the laser-energy coupling with nanostructure targets and radiation sources, and motivate the wakefield acceleration in solid density plasma.

Figure 1

(a) Snapshot of the current density $J_x$ at $t=13\mathrm{fs}$. The laser pulse travels from left to right. Electrons are stripped off from the surface of the nanowire and moved to the right, indicated by the forward current (blue). The return current (red) is created at the surface of the nanowire. A plasma wave is excited inside the nanowire as indicated by the sinusoidal current density. (b) The longitudinal density perturbation $\delta n_e/n_0$ (solid line) and wakefield $E_x$ (dashed line in normalized unit) at $y=0$. Here, $n_0=60n_{\mathrm{cr}}$ is the average electron density created by the field ionization along the nanowire. (c) The frequency spectrum associated with the current density shown in (a). The dashed line indicates the plasma frequency of ${\omega }_{\mathrm{pe}}=7.75{\omega }_{\mathrm{L}}$.

Figure 2

Longitudinal electron phase space at $t=13\mathrm{fs}$, demonstrating the presence of $2{\omega }_{\mathrm{L}}$ electron bunches inside the nanowire. The phase space is restricted at $-0.1\mu \mathrm{m}\le y\le 0.1\mu \mathrm{m}$ to exclude electrons in the skin layer and outside the nanowire. The inset shows the enlarged phase space for $2\mu \mathrm{m}\le x\le 3\mu \mathrm{m}$ with the plasma wavelength ${\lambda }_{\mathrm{p}}\approx 100\mathrm{nm}$.

Figure 3

(a) Snapshot of electron macroparticles with $\gamma \ge 2$ at $t=13\mathrm{fs}$. Electrons outside the nanowire move in the $+y$ direction when $E_y<0$ and in the $-y$ direction when $E_y>0$, respectively. The $2{\omega }_{\mathrm{L}}$ electron bunches inside the nanowire propagates in the forward direction. The solid, dashed, and dash-dotted lines indicate three trajectories of three sample electrons until $t=20\mathrm{fs}$. (b),(c) The $\gamma$ of the corresponding electrons in (a). The arrows in (a) indicate the electrons entering the nanowire boundary and their corresponding $\gamma$ in (b). The dashed white line indicates the boundary of the nanowire of diameter $d$.

Figure 4

Electron energy spectra at $t=20\mathrm{fs}$ for nanowire (solid line) and flat target (dashed line) within the region $-0.1\mu \mathrm{m}\le y\le 0.1\mu \mathrm{m}$.

Figure 5

The current density at $t=20\mathrm{fs}$ for (a) nanowire, and (b) flat target. Both targets have the same length. The energy spectra are calculated for the region between the green lines. The arrows indicate the physical processes with the terms used in the text.

Figure 6

3D simulation results with picongpu code for linearly polarized laser field at $t=13\mathrm{fs}$. (a) The isosurface of electron density at $n_e=4n_{\mathrm{cr}}$. (b) The frequency spectrum associated with the longitudinal current density $J_y$. (c) The longitudinal electron phase space inside the nanowire. (d) The current density components, $J_y$ taken at $z=1\mu \mathrm{m}$. (e) The longitudinal density perturbation (solid line) and wakefield (dashed line) along the nanowire center. (f) The total electron energy spectra at $t=20\mathrm{fs}$ with the one inside the nanowire. (g) The transverse current components. (h) The transverse current density $J_x$ where the dashed boxes indicate the returning electron that will cross the nanowire with the corresponding transverse momentum, $p_x/\left(mc\right)$ in (i). (j) The transverse momentum component $p_z/\left(mc\right)$.