Monoenergetic electron bunches generated from thin solid foils irradiated by ultrashort, ultraintense circularly polarized lasers

Future ultrashort ${10}^{22}–{10}^{25}\mathrm{W}{\mathrm{cm}}^{-2}$ laser pulses offer the possibility of producing ultrashort monoenergetic electron beams in the GeV–TeV level by direct laser ponderomotive force acceleration (LPFA) in distances of millimeters to about 1 m. A scheme is proposed that a thin solid foil and a thick solid foil are placed on the laser axis, where the thin foil supplies the electron source for LPFA and the thick foil reflects the laser away, however allows the accelerated electrons to go through. By optimizing the distance between the foils, one can obtain the maximum electron beam energy. This scheme is demonstrated by particle-in-cell simulations.

Figure 1

Schematic plot for laser ponderomotive force acceleration, where a thin solid foil (source foil) provides the electron source for laser acceleration and a thick solid foil (laser-blocking foil) blocks the laser when the electrons reach the maximum energy.

Figure 2

Snapshots of the distributions of the electron number versus electron positions and energy are shown by the red curves. The blue curves in every plot of the left column are $1/1000$ of the laser electric field $E_y$ normalized by $m_{e}c{\omega }_0/e$ to show the position of the electron beam in the acceleration or deceleration phase of the ponderomotive field, where the acceleration phase is within the leading edge of the laser pulse ($2T_0/\mu \mathrm{m}$ long) and the deceleration phase is within the trailing edge of the laser pulse ($2T_0/\mu \mathrm{m}$ long). The four rows are the results at the time of 1, 2.47, 3.15, and 8 ps, respectively.

Figure 3

Distributions of electron energy versus $\xi =t-x$ at different time, where the acceleration phase of the ponderomotive field is within $0<\xi <2$ and the deceleration phase within $2<\xi <4$.

Figure 4

The average energy, energy spread (the calculation method following Refs. 14, 15), and charges of the electron beam as a function of time, where the curves with different colors in every plot denote the source foils with different thickness, the broken line in (a) given by the single electron model, and only the electrons within the laser pulse ($0\le \xi \le 4$) are counted.

Figure 5

Snapshots of the spatial distributions of the laser electric field interacting with source foils of different thickness.

Figure 6

(a) Spatial distributions of the laser electric field $E_y$ and electron density $n_e$, as well as (b) the distributions of the electron number as functions of electron energy and divergence angle at different time, where the laser-blocking foil is located at $x=618.5\mu \mathrm{m}$.

Figure 7

Distributions of the electron number with electron energy and divergence angle at 2.01 ps obtained from two respective simulations. In simulation (a), the source foil with the infinite transverse size is taken. In simulation (b), the source foil with the thickness of $1\mu \mathrm{m}$ and the density of $0.1n_c$ is taken.