  The relativistic quantum dynamics of an electron in an intense single-mode
quantized electromagnetic field is investigated with special emphasis on the
spin degree of freedom. In addition to fast spin oscillations at the laser
frequency, a second time scale is identified due to the intensity dependent
emissions and absorptions of field quanta. In analogy to the well-known
phenomenon in atoms at moderate laser intensity, we put forward the conditions
of collapses and revivals for the spin evolution in laser-driven electrons
starting at feasible $10^{18}$ W/cm$^2$.
