Spin polarization of electrons by ultraintense lasers

Electrons in plasmas produced by next-generation ultraintense lasers (I>5×10²²0.16em0exW/cm²) can be spin polarized to a high degree (10%--70%) by the laser pulses on a femtosecond time scale. This is due to electrons undergoing spin-flip transitions as they radiate γ-ray photons, preferentially spin polarizing in one direction. Spin polarization can modify the radiation reaction force on the electrons, which differs by up to 30% for opposite spin polarizations. Consequently, the polarization of the radiated γ-ray photons is also modified: the relative power radiated in the σ and π components increases and decreases by up to 30%, respectively, potentially reducing the rate of pair production in the plasma by up to 30%.