Dynamic trajectories of relativistic electrons injected into tightly-focused intense laser fields

摘要

Dynamic trajectories of relativistic electrons injected into tightly focused ultra-intense laser field have been investigated. In addition to the previously-reported CAS (Capture and Acceleration Scenario) and IS (Inelastic Scattering) trajectories, a new kind of nonlinear electron trajectory is found when the beam waist radius w(0) is small enough (kw(0) less than or equal to 30, k is the wave number) and incident angle is small. We shall call it PARM (Penetrate into Axial Region and Move). The basic feature of PARM trajectory shows the strong diffraction effect of a tightly-focused laser field. Part of the incident electrons that experience the strong transversal force from the diffraction edge field as they travel toward the beam waist will follow the PARM trajectory. This force can push the electrons toward the beam center. Thus unlike the CAS and IS electrons, the PARM electrons will move along the region near the beam axis. We also found some of the PARM electrons can gain energy from the field. The conditions for PARM electrons to appear were examined and are presented here. The implication of the presence of PARM to the planned experimental test of the CAS scheme is addressed.