Probing Strong-Field QED with Doppler-Boosted Petawatt-Class Lasers

We propose a scheme to explore regimes of strong-field quantum electrodynamics (SF QED) otherwise unattainable with the currently available laser technology. The scheme relies on relativistic plasma mirrors curved by radiation pressure to boost the intensity of petawatt-class laser pulses by Doppler effect and focus them to extreme field intensities. We show that very clear SF QED signatures could be observed by placing a secondary target where the boosted beam is focused.

Figure 1

Sketch of the scheme proposed in this Letter. (a) A plasma mirror shaped by radiation pressure converts an intense laser pulse into Doppler-boosted harmonics and focuses them on a secondary target, reaching extreme intensities. (b),(c) Electric field of a 10-PW infrared laser beam ($2\mu \mathrm{m}$ waist) and of the generated Doppler-boosted beam at focus (both normalized to the critical field $E_S$). Note the strong change in field amplitude ($\sim \times 33$ enhancement).

Figure 2

Simulation results for a 10-PW standard laser (top panels) and a Doppler-boosted beam obtained with a 10-PW laser (bottom panels), shown $\sim 10\mathrm{fs}$ after the peak of the pulse has reached the target. (a),(d) Magnetic field. (b),(e) High-energy ($E>2m_e{c}^2$) photon density. (c),(f) Generated positron macroparticles. The black line marks the isodensity curve $n_e=100n_c$.

Figure 3

Interaction of a 10-PW Doppler-boosted beam with the secondary target. (a),(b) Simulation snapshots showing, respectively, the emission of a high-energy photon from a target electron and the decay of this photon into a pair. Electron density is shown in gray scale, while the transverse component of the magnetic field is shown in blue-red color scale. (c) Transverse component of the magnetic field. (d),(e) Respectively, electron and photon phase-space projection on the $(x,\chi )$ plane. (f),(g) Scatter plot, respectively, of electrons and photons in the $(p_x,p_z)$ plane, with $\chi$ value encoded in color. Plots in (c)–(g) concern particles located in the interaction region, in a $4\mu \mathrm{m}\times 2\mu \mathrm{m}$ box, $\sim 2.5\mathrm{fs}$ after the peak of the pulse has reached the target.

Figure 4

Respectively, (a) maximum ${\chi }_e$ and (b) number of generated positrons per laser shot as a function of laser power. For the standard laser we did not observe pair generation events below 6.5 PW.

Figure 5

Overview of the maximum $\chi$ parameter attainable with different schemes: ultrarelativistic electrons propagating in crystalline fields [13, 14], the E-144 experiment performed at SLAC [37], the wakefield-based experiment performed at Rutherford Appleton Laboratory (RAL) [39], the E-340 experiment proposed at SLAC [40, 41], the three phases of the LUXE [41, 42] experiment proposed at DESY, and finally the schemes based on Doppler-boosted beams presented in this Letter.