Polarization separator created by a filament in air

We demonstrate that a femtosecond laser pulse-induced filament can act as a "polarization separator" for a copropagating femtosecond probe pulse. The probe component with polarization parallel to the pump is guided along the propagation axis through the cross interactions with the pump pulse. And the probe component with polarization orthogonal to that of the pump is diffracted out into an outer ring by the plasma. The extinction ratio (I(probe)(min) / I(probe)(max)) along the propagation axis is better than 1:20.