Relativistic Ponderomotive Hamiltonian 
of a Dirac Particle in a Vacuum Laser Field

Authors:  D.E. Ruiz, C.L. Ellison, I.Y. Dodin

Abstract:  We report a point-particle ponderomotive model of a Dirac electron oscillating in a high-frequency field.  Starting from the Dirac Lagrangian density, we derive a reduced phase-space Lagrangian that describes the relativistic time-averaged dynamics of such a particle in a geometrical optics laser pulse propagating in vacuum.  The pulse is allowed to have an arbitrarily large amplitude provided that radiation damping and pair production are neglibible.  The model captures the Bargmann-Michel-Telegdi (BMT) spin dynamics, the Stern-Gerlach spin-orbital coupling, the conventional ponderomotive forces, and the interaction with large-scale background fields (if any).  Agreement with the BMT spin precession equation is shown numerically.  The commonly known theory, in which ponderomotive effects are incorporated in the particle effective mass, is reproduced as a special case when the spin-orbital coupling is negligible.  This model could be useful for studying laser-plasma interactions in relativistic spin-1/2 plasmas.
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Submitted to:  Physical Review A
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Download PPPL-5204 (pdf 2.9 MB 19 pp)
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