Modulation of attosecond beating by resonant two-photon transition

TL;DR

This paper introduces an analytical model for two-photon transitions involving autoionising states, explaining phase variations in resonant RABITT spectra and revealing new phase behaviors differing from previous observations.

Contribution

The paper develops a novel analytical model that captures phase variations in resonant two-photon transitions, providing new insights into autoionising state effects in attosecond spectroscopy.

Findings

Phase of sideband beating varies significantly with photon energy near resonance.

The phase variation differs from the typical π jump seen in non-resonant cases.

A geometrical representation helps visualize phase profiles in resonant transitions.

Abstract

We present an analytical model that characterizes two-photon transitions in the presence of autoionising states. We applied this model to interpret resonant RABITT spectra, and show that, as a harmonic traverses a resonance, the phase of the sideband beating significantly varies with photon energy. This phase variation is generally very different from the $\pi$ jump observed in previous works, in which the direct path contribution was negligible. We illustrate the possible phase profiles arising in resonant two-photon transitions with an intuitive geometrical representation.