Intense nonlinear laser field longitudinal vector potential breaks motion symmetry of stimulated electron and produces highly collimated radiation

The effects of longitudinal fields on electron dynamics, power, and radiation spectrum in tightly-focused circularly polarized laser pulses are investigated in detail. When the longitudinal field vector potential is not considered at the intense relativistic laser field, the longitudinal acceleration of the electron subjected to the ponderomotive force is oscillatory, and the electron will be pushed out of the laser field. The peak radiation power, along with peak angle, varies exponentially with the laser peak amplitude. The longitudinal field leads to the appearance of spatial radiation vortex states when the laser peak is strong, increasing the collimation of the power and spectrum of spatial radiation as well as the focus.