SIGNATURE OF RELATIVISTIC EFFECTS IN ATOM-LASER INTERACTIONS AT ULTRAHIGH INTENSITIES

With the help of a theoretical analysis supported by numerical simulat ions, we show that one can observe unambiguous relativistic effects in atom-laser interactions in the regime of ultrahigh intensities. These effects, which can be observed in the high frequency stabilization re gime, differ from ordinary high-Z relativistic corrections and also fr om those resulting from standard relativistic dynamics of free electro ns in a plasma. Their signature is the occurrence of notable modificat ions in above-threshold-ionization spectra resulting from a two-color scheme involving simultaneously a high frequency and a low frequency f ield.