Progress of Probing Strong-Field Laser Electron Interaction at FACET-II*

The 1990’s SLAC Experiment-144  measured the onset of  QED nonlinearities in laser-electron interactions, including multi-photon Compton scattering and electron-positron pair production [1, 2]. E-144 has since stimulated a worldwide endeavor to access the transition from the perturbative multiphoton to the non-perturbative tunneling regime of QED, which is still unexplored experimentally [3]. Recent advances in laser technology combined with the Lorentz boost of multi-GeV electron beams enables us to experimentally explore this strong-field QED (SFQED) regime, where the laser intensity reaches or even exceeds the QED critical (Schwinger) scale in the center-of-momentum frame.

Here, we report recent progress of the SLAC Experiment 320 that investigates the SFQED regime at the FACET-II facility [4]. Our scheme is based on the collision of ~10 TW laser pulses with the FACET-II 10 GeV e-beam at a ~150^o crossing angle.  We describe our experimental approaches, specifically the technique of fine tuning of the spatial-temporal overlap. We also present recent  experimental results from the latest FACET-II run that successfully demonstrate higher order nonlinear Compton scattering signals from the laser-e-beam collision, as well as future plans and experimental development.

[1]     C. Bula et al., “Observation of nonlinear effects in Compton scattering,” Phys. Rev. Lett. 76, 3116-3119 (1996).

[2]     D. Burke et al., “Positron production in multi-photon light by light scattering,” Phys. Rev. Lett. 79, 1626-1629 (1997).

[3]     S. Meuren et al., “Semiclassical picture for electron-positron photoproduction in strong laser fields,” Phys. Rev. D 93, 085028 (2016).

[4]     V. Yakimenko, et al., “FACET-II facility for advanced accelerator experimental tests,” Phys. Rev. Accel. Beams 22, 101301 (2019).