Electron spin polarization in Gaussian and super-Gaussian shaped chirped electric fields

Abstract In this study, a comprehensive theoretical and numerical analysis is conducted to investigate the dynamical mechanisms underlying electron spin polarization in a rotating electric field generated by two counterpropagating Gaussian laser pulses with distinct chirping profiles and envelope shaping characteristics. The effects of both positive and negative frequency chirping are examined, where the introduction of chirp breaks the temporal symmetry of the electric field, thereby altering electron dynamics and influencing the resulting degree of spin polarization. Additionally, modifications to the field envelope shape are shown to significantly affect electron trajectories and energy acquisition at different temporal phases, which in turn modulates the quantum electrodynamics parameter and the extent of spin polarization. The results demonstrate that under linearly chirped conditions, symmetric and asymmetric Gaussian envelopes, as well as super-Gaussian envelopes (with order n = 8), yield relatively weak polarization at the magnetic node, producing spin polarization degrees of approximately 3% and 28.68%, respectively. In contrast, negatively chirped asymmetric Gaussian fields enhance spin polarization, achieving a maximum degree of 56.79%. Moreover, the combination of super-Gaussian envelope shaping and negative chirping is found to simultaneously increase the net energy gain and the probability of radiation-induced spin flips. Notably, a super-Gaussian field ( n = 8) with negative frequency chirp achieves a spin polarization degree of up to 84.42%, indicating a substantial improvement over other configurations.