  The semiclassical dynamics of a charged spin-1/2 particle in an intense
electromagnetic plane wave is analyzed beyond the electric dipole approximation
and taking into account the leading relativistic corrections to the Pauli
equation. It is argued that the adiabatic spin evolution driven by a low
intensity radiation changes its character drastically as an intensity of a
laser is increasing. Particularly, it is shown that a charged particle exposes
a spin flip resonance at a certain pick value of a laser field strength, which
is determined by a particle's gyromagnetic ratio.
