Energy gain of injected electrons subjected to an intense laser field and its magnetic field induced in plasma

Cyclotron-resonance energy gain of injected electrons subjected to an intense circularly polarized laser field and the magnetic field induced in a low-density plasma is investigated theoretically. By considering the inverse Faraday effect (IFE), where a circularly polarized finite area laser beam induces an axial magnetic field in a plasma, it is found that very interesting energy gains can be obtained by Doppler-shifted cyclotron resonance in this field for the appropriate injection velocity. This same IFE field also acts to confine these electrons radially and, on exiting the plasma adiabatically, it is in this way that the transverse electron energy is converted to axial energy. Two limits to the energy gain are discussed: (i) cyclotron radius of the energetic electrons becoming comparable to the beam, and (ii) axial dephasing.