Dense Electron-Positron Plasmas and Ultraintense $\gamma$ rays from Laser-Irradiated Solids

In simulations of a 10 PW laser striking a solid, we demonstrate the possibility of producing a pure electron-positron plasma by the same processes as those thought to operate in high-energy astrophysical environments. A maximum positron density of ${10}^{26}{\mathrm{m}}^{-3}$ can be achieved, 7 orders of magnitude greater than achieved in previous experiments. Additionally, $35\%$ of the laser energy is converted to a burst of $\gamma$ rays of intensity ${10}^{22}\mathrm{W}{\mathrm{cm}}^{-2}$, potentially the most intense $\gamma$-ray source available in the laboratory. This absorption results in a strong feedback between both pair and $\gamma$-ray production and classical plasma physics in the new “QED-plasma” regime.

Figure 1

Pair production by a laser of intensity $4\times {10}^{23}\mathrm{W}{\mathrm{cm}}^{-2}$ striking an aluminum target (snapshots at the end of the 30 fs laser pulse). The laser (red contours) bores a hole into the solid target (blue density map). $\gamma$ rays (blue density map) and positrons (red dots) are generated in this interaction (inset—on the same scale).

Figure 2

Electron and positron energy spectra in the interaction of a laser of intensity $4\times {10}^{23}\mathrm{W}{\mathrm{cm}}^{-2}$ with solid aluminum (spatially and temporally integrated). As usual, the electron spectrum has a pronounced tail of “fast electrons.” The corresponding $\gamma$-ray spectrum is represented in the inset.

Figure 3

$\gamma$-ray intensity averaged over one laser period for a laser intensity of $8\times {10}^{23}\mathrm{W}{\mathrm{cm}}^{-2}$ 25 fs after the end of the incident laser pulse (when all the photons leave the target).