Relativistic plasma aperture for laser intensity enhancement

A substantial increase in local laser intensity is observed in the near field behind a plasma shutter. This increase is caused by the interference of the diffracted light at the relativistic plasma aperture and it is studied both analytically and using numerical simulations. This effect is only accessible in the regime of relativistically induced transparency and thus it requires a careful choice of laser and target parameters. The theoretical estimates for the maximum field strength and its spatial location as a function of target and laser parameters are provided and compared with simulation results. Our full 3D particle-in-cell simulations indicate that the laser intensity may be increased roughly by an order of magnitude, improving the feasibility of strong field QED research with the present generation of lasers.

Figure 1

Schematic of target geometry during the interaction with (a) $s$-polarized and (b) $p$-polarized laser pulse. (c) Minimal and (d) characteristic aperture radius for penetration of the foil.

Figure 2

The intensity of the $s$-polarized laser pulse and the density of target electrons for $I_0={10}^{22}\mathrm{W}/{\mathrm{cm}}^2$ and $\lambda =805\mathrm{nm}$. Target thickness is 30 nm. Black contours in electron density represent the relativistic critical density $n_{\mathrm{c}\gamma }^{\mathrm{avg}}$.

Figure 3

The intensity of the $p$-polarized laser pulse and the density of target electrons for $I_0={10}^{22}\mathrm{W}/{\mathrm{cm}}^2$ and $\lambda =805\mathrm{nm}$. Target thickness is 30 nm. Black contours in electron density represent the relativistic critical density $n_{\mathrm{c}\gamma }^{\mathrm{avg}}$.

Figure 4

(a) Longitudinal position of the maximum field strength at the rear side of the target given by Eqs. (9) and (12) and obtained from PIC simulation. (b) The ratio of the first ten harmonics of the scattered light to the incident field of strength $E_0$ obtained from PIC simulations and compared to the theory described in Refs. [24, 25] for $p$-polarized laser beam.

Figure 5

The electric field intensity distribution in $k_x-k_y$ phase-space for (a) $s$ and (b) $p$ polarization at the same time step as in Figs. 2 and 3. The laser of intensity $I_0={10}^{22}\mathrm{W}/{\mathrm{cm}}^2$ and wavelength $\lambda =805\mathrm{nm}$ irradiates the 30-nm-thick target.

Figure 6

Maximum intensity $I$ achieved in the interaction of the $s$- and $p$-polarized Gaussian laser beam characterized by $I_0={10}^{22}\mathrm{W}/{\mathrm{cm}}^2$ with the target of different thickness. Lines represent the expected values given by Eqs. (4) and (5), markers show the results obtained from PIC simulations. The relativistically corrected skin depth is $42\mathrm{nm}$.

Figure 7

The distribution of the laser intensity in horizontal and vertical slices of the laser pulse after the interaction with a foil as obtained from 3D simulation.

Figure 8

The distribution of the laser intensity in the horizontal slice of the laser pulse as obtained from 3D simulation at the moment of reaching the maximum value.