Ab Initio Approach To The Study Of Transient States And Ultra-Fast Processes: Application to Argon

Thomas Carette

Thursday, 13 December 2012, 13:15
Matfys library

Recent advances in attosecond XUV pulse generation pave the way for time-resolved investigation and control of electron wave-packets [1]. However, the models used for interpreting those experiments often neglect the underlying many-electron processes that unfold on the same time-scale as the photoelectron emission.

We report on the development of a package that aims at integrating the Time-Dependent Schrödinger Equation (TDSE) including many-body effects, as well as providing reliable ab initio data of use in atomic attophysics in a time-independent framework, e.g. photoelectron phases ? which relate to so-called photoionization time delays ?, multi-photon ionization cross- sections, and resonance properties. We follow a configuration interaction approach with orbitals expended on B-spline basis sets. For dealing with the complicated angular integration involved in computing matrix elements, we use the Atomic Structure Package (ATSP2K) [2]. In order to avoid problems due to the finite box in time independent computations, we solve the many-body problem along complex radial coordinates, i.e. using the Exterior Complex Scaling method.

This package is tested by performing a detailed study of the photoionization of Argon with photon energy ranging from 26 eV to 44 eV. Below 30 eV, a close-coupling expansion targeting the description of the 3snp series of autoionizing states is used. The computed resonance parameters and photoelectron angular distribution agrees with previous R-matrix calculations and experiments [3]. Recent experiments have reported photoionization relative delay between 3s and 3p ionization at 34.1, 37.2 and 40.3 eV photon energy [4]. We present preliminary results showing that this delay is strongly affected by many nearby correlation satellite states. However, smoothed curve for the relative delay shows a satisfying agreement with experiment.

1. Krausz and Ivanov, Rev. Mod. Phys. 81, 163 (2009)
2. Froese Fischer et al., Comp. Phys. Comm. 176, 559 (2007)
3. Berrah et al., J. Phys. B 29, 5351 (1996)
4. Klünder et al., Phys. Rev. Lett. 106, 143002 (2011), Guénot et al., Phys. Rev. A 85 53424 (2012)