Highly polarized energetic electrons via intense laser-irradiated tailored targets

A method for the generation of ultrarelativistic electron beams with high spin polarization is put forward, where a tightly focused linearly polarized ultraintense laser pulse interacts with a nonprepolarized transverse-size-tailored solid target. The radiative spin polarization and angular separation is facilitated by the standing wave formed via the incident and reflected laser pulses at the overdense plasma surface. Strong electron heating caused by transverse instability enhances photon emission in the density spikes injected into the standing wave near the surface. Two groups of electrons with opposite transverse polarization emerge, antialigned to the magnetic field, which are angularly separated in the standing wave due to the phase-matched oscillation of the magnetic field and the vector potential. The polarized electrons propelled into the plasma slab are focused at the exit by the self-generated quasistatic fields. Our particle-in-cell simulations demonstrate the feasibility of highly polarized electrons with a single 10 PW laser beam, e.g., with polarization of 60% and charge of 8 pC selected at energy of 200 MeV within 15 mrad angle and 10% energy spread.