Phase-resolved attosecond near-threshold photoionization of molecular nitrogen

TL;DR

This study uses phase-resolved attosecond pulses to investigate near-threshold photoionization of nitrogen molecules, revealing phase shifts linked to resonances and enabling access to ultrafast state dynamics.

Contribution

It introduces a high-resolution method for measuring molecular phases during photoionization, unveiling complex resonance effects in nitrogen.

Findings

Observed a 0.76 π phase shift in ionization channels

Linked phase shifts to the presence of complex resonances

Provided a new approach to study ultrafast molecular states

Abstract

We photoionize nitrogen molecules with a train of extreme ultraviolet attosecond pulses together with a weak infrared field. We measure the phase of the two-color two-photon ionization transition (molecular phase) for different states of the ion. We observe a 0.76 $\pi$ shift for the electrons produced in the ionization channels leading to the X$^2 \Sigma_g^+$, $v'=1$ and $v'=2$ states. We relate this phase shift to the presence of a complex resonance in the continuum. By providing both a high spectral and temporal resolution, this general approach gives access to the evolution of extremely short lived states, which is hardly accessible otherwise.