LAUSR

We propose a method to generate circularly polarized (CP) attosecond pulses by the interactions of a relativistic-intensity right-hand CP laser pulse and magnetized sub-critical plasma. It is theoretically and numerically demonstrated that when an external magnetic field with an appropriate strength is applied to a sub-critical plasma along the laser propagation, the ponderomotive force of a right-hand CP laser at the vacuum-plasma boundary is significantly enhanced. The electrons are then steadily pushed forward until the timely-increasing charge separation field becomes strong enough to pull them back, forming a dense and counter-moving electron sheet. The relativistic-velocity electron sheet works as a flying mirror to compress the tail of the driving laser and efficiently generate a single CP attosecond pulse. The present scheme shows a stable efficiency on different scale lengths of preplasma and thus may provide a robust way to generate bright and CP attosecond pulses.