Relativistic effects in laser-atom interactions

Relativistic effects arise when atoms interact with ultrastrong laser field s. Such effects are expected to become important when the ratio of the pond eromotive energy U-p of an electron in the field to the electron rest mass energy mc(2) becomes comparable to unity. this rtio is given by q = e(2)E(0 )(2)/(4m(2)omega (2)c(2)), where E-0 is the peak strength of the electric f ield, omega is the angular frequency of the laser light and e is the magnit ude of the electron charge. We discuss recent progress in the theoretical s tudy of several relativistic effects in laser-atom interactions: influence of the magnetic component of the laser field, relativistic mass shift due t o the dressing of the electron mass by the laser field, negative energy sta tes and spin effects. Particular attention is paid to the modifications of the laser-atom dynamics in the high-intensity, high-frequency regime.