Theory of Attosecond Transient Absorption Spectroscopy of Krypton for Overlapping Pump and Probe Pulses

TL;DR

This paper presents the first ab initio theoretical calculations of attosecond transient absorption spectroscopy of krypton with overlapping pump and probe pulses, revealing how the absorption features relate to ionization dynamics and laser-induced phase shifts.

Contribution

It extends the TDCIS model to include spin-orbit effects and provides a detailed theoretical analysis of experimental spectral features during overlapping pulses.

Findings

Absorption signals relate directly to instantaneous hole populations.

Strong deformations occur in absorption lines at maximum pulse overlap.

Laser dressing of the N-electron wave function causes phase shifts in ionic dipoles.

Abstract

We present the first fully ab initio calculations for attosecond transient absorption spectroscopy of atomic krypton with overlapping pump and probe pulses. Within the time-dependent configuration interaction singles (TDCIS) approach, we describe the pump step (strong-field ionization using a near-infrared pulse) as well as the probe step (resonant electron excitation using an extreme- ultraviolet pulse) from first principles. We extent our TDCIS model and account for the spin-orbit splitting of the occupied orbitals. We discuss the spectral features seen in a recent attosecond transient absorption experiment [A. Wirth et al., Science 334, 195 (2011)]. Our results support the concept that the transient absorption signal can be directly related to the instantaneous hole population even during the ionizing pump pulse. Furthermore, we find strong deformations in the absorption lines when the overlap of pump and probe pulses is maximum. These deformations can be described by relative phase shifts in the oscillating ionic dipole. We discuss possible mechanisms contributing to these phase shifts. Our finding suggests that the non-perturbative laser dressing of the entire N -electron wave function is the main contributor.