INFLUENCE OF SCREENING OF THE COULOMB POTENTIAL ON THE PLATEAU IN ABOVE-THRESHOLD IONIZATION

We present a generalization of the Keldysh-Faisal-Reiss model that inc ludes the second-order S-matrix element and thus the effects of rescat tering. On the example of a screened Coulomb potential we show that us ing our model it is possible to reproduce all main features of the rec ent experimental results, mainly, the appearance of a plateau, the pos ition of the cutoff, and the side lobes. We also show that the differe nce between the direct ionization probability and the rescattering pla teau for a long-range Coulomb-like potential (with a small screening p arameter) is very large, which is in discrepancy with the experimental results. This indicates that the effective potential that an electron feels during the rescattering is not a pure Coulomb potential. We sho w that this potential can be approximated by a screened Coulomb potent ial with a properly chosen screening parameter.