We reconsider the problem of particle acceleration by large-amplitude electromagnetic waves. We make use of a fully relativistic Hamiltonian formalism to show that, as opposed to nonelativistic results obtained by Kuo and Lee, acceleration in unmagnetized systems is severely arrested when the phase velocity of the electromagnetic mode approaches the speed of light. For subluminal waves, however, acceleration is shown to be still effective.
Journal of Plasma Physics. Cambridge. vol. 57, n. 4 (may/june 1997), p. 785-792