  Here, we demonstrate the radiative polarization of high-energy electron beams
in collisions with ultrashort pulsed bi-chromatic laser fields. Employing a
Boltzmann kinetic approach for the electron distribution allows us to simulate
the beam polarization over a wide range of parameters and determine the optimum
conditions for maximum radiative polarization. Those results are contrasted
with a Monte-Carlo algorithm where photon emission and associated spin effects
are treated fully quantum mechanically using spin-dependent photon emission
rates. The latter method includes realistic focusing laser fields, which allows
us to simulate a near-term experimentally feasible scenario of a 8 GeV electron
beam scattering from a 1 PW laser pulse and provide a measurement that would
verify the ultrafast radiative polarization in high-intensity laser pulses that
we predict. Aspects of spin dependent radiation reaction are also discussed,
with spin polarization leading to a measurable (5%) splitting of the energies
of spin-up and spin-down electrons.
