Coulomb-Corrected Strong Field Approximation without Singularities and Branch Points

TL;DR

This paper develops a Coulomb-Corrected Strong Field Approximation that avoids singularities and branch points, improving the semi-classical analysis of electron ionization in laser fields within certain intensity regimes.

Contribution

It introduces an effective action free of Coulomb singularities using the Magnus expansion, enhancing the theoretical framework for strong field ionization analysis.

Findings

Effective action free of Coulomb singularities and branch points.

Classical action recovered as asymptotic limit of the effective action.

Applicability discussed for specific laser intensities.

Abstract

The domain of validity of the Coulomb-Corrected Strong Field Approximation (CCSFA) is going to be analyzed in relation to the semi-classical dynamics of electrons during ionization of hydrogen-like targets. Our analysis is limited to ionization driven by Ti-sapphire laser pulses with intensities up to roughly 10$^{14}$ Wcm$^{-2}$. For such parameters, the effects related to radiation pressure are small and the laser field can be described in the dipole approximation. By applying the Magnus expansion for the exact retarded electron propagator we obtain an {\it effective action} which is free of Coulomb singularities and branch points when the complex-time trajectories are used. Furthermore, we show that the classical action is exactly recovered as the asymptotic limit of its effective counterpart. The applicability of such limit is also discussed.