Strong laser field effects in autoionization

We derive a parametrized formula for the photoionization cross section in the vicinity of an autoionizing state (AIS) coupled with another AIS by a strong laser field. The rotating-wave approximation is used and adiabaticity is assumed. In the probe field spectrum two Fano resonances contribute to the cross section, while a single resonance occurs in the strong-field spectrum. The correlation between the resonance shape and the complex energies of the laser-driven two-level system is described. Calculations are performed for the 2s2p(1)P and 2s3d D-1 AIS pair in He and for the 3p(21)S and 3p3d(1)P pair in Mg. The results agree with those obtained using time; dependent approaches. The formula for the cross section describes the spectral features of the ion yield measured in the two-photon ionization of the Mg atom via the 3p(21)S AIS coupled with the 3p3d(1)P state. The appearance of laser-induced degenerate states in the cross section shape is studied.