In laser-cluster interactions, we believe that the account for screening phenomena in the nanoplasma model [1] should reduce the discrepancies between theory and experiments for the high charge states measured. Indeed, screening strongly modifies the atomic structure of ionic species, and, consequently the magnitude of the collisional processes leading to highly charged ions. These effects have to be very important in the early stage of the interaction when the plasma is degenerate, before evolving towards a more classical one. Therefore, the screening method has to be sufficiently sophisticated to account for the evolution of the plasma conditions.
In ion-surface collisions, an impinging particle is subject to increasing values of the electronic density as it approaches to the surface. Then, its atomic structure is modified during the interaction. As the electron exchange transition rates are extremely sensitive to the atomic description [2], the screening effect has to be explicitely considered in the theory.
Gupta and Rajagopal (GR) [3] have proposed a sophisticated screening approach based on the finite temperature Lindhard dielectric function. This method has not been often used, probably because of the complexity of its implementation. In this work, we compare from a practical point of view the GR approach with analytical models currently used: Debye-Huckel (DH), Thomas-Fermi (TF), Static Screened Coulomb (SSC) and Ionic-Sphere (IS). Then, we deduce practical limits for the validity of these models and we show that the GR approach is needed to represent accurately the screening effects in laser-cluster and ion-surface interactions.

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