Special features of motion of particles in an electromagnetic wave

The behavior of a charged particle in the field of a monochromatic electromagnetic wave is considered. The motion of a particle is determined not only by the wave field but also by the initial conditions. The trajectories of particles are calculated both by using the exact solution and by employing perturbation theory in the parameter η = eE/(mcω), the ratio of the energy the field transfers to a particle over a wavelength, to the particle's rest energy. Two kinds of electromagnetic waves, those with coordinate independent amplitudes (uniform waves) and those with coordinate dependent amplitudes (non-uniform waves) are treated. The motion of particles that either are at rest or move with prescribed velocity at the initial time, is investigated. It is shown that a charged particle performs not only an oscillatory motion but also a systematic drift in the field of a wave. In a non-uniform wave, accelerating ponderomotive forces also act on a particle.