GUIDING-CENTER EQUATIONS FOR ELECTRONS IN ULTRAINTENSE LASER FIELDS

The guiding-center equations are derived for electrons in arbitrarily intense laser fields also subject to external fields and ponderomotive forces. Exhibiting the relativistic mass increase of the oscillating electrons, a simple frame-invariant equation is shown to govern the be havior of the electrons for sufficiently weak background fields and po nderomotive forces. The parameter regime for which such a formulation is valid is made precise, and some predictions of the equation are che cked by numerical simulation.