| Time-averaged over a field cycle forces acting on charged particles in a spatially inhomogeneous electromagnetic field are usually called Ponderomotive Forces. In the nonrelativistic regime these forces always push the particles away from high-field areas and into the low-field areas. In many cases these forces have a non-relativistic nature. However, in many applications, with advent of laser technology, Ponderomotive forces can enter into a strongly relativistic domain.Considering quasi-optical and geometrical optics approximations, we show a theoretical extension on fully relativistic ponderomotive force acting upon charges in electromagnetic waves. As an example, the general expressions for a ponderomotive force acting upon a relativistic charge in the field with circular polarization are found. These expressions are analyzed for the specific case of a strong laser fields. Under these conditions, the structure of ponderomotive forces is more complex than in the nonrelativistic case and is defined, in general, by all even powers of the electric field amplitude. Nevertheless, for this case, the ponderomotive force still can be described by one scalar function with effective mass m* depending on the field amplitude E. A “ well defined” expression for the averaged Lorenz factor is given |
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