Phase measurement of a Fano window resonance using tunable attosecond pulses

TL;DR

This paper investigates the phase and amplitude of argon atom photoionization near a Fano resonance using attosecond pulse trains and interferometry, combining experimental measurements with theoretical modeling.

Contribution

It introduces an interferometric method with attosecond pulses to measure phase variations in photoionization near a Fano resonance, supported by detailed theoretical analysis.

Findings

Phase variation depends on channel interactions in autoionization.

Experimental data matches theoretical predictions.

Method enables precise phase measurements in ultrafast photoionization.

Abstract

We study the photoionization of argon atoms close to the 3s$^2$3p$^6$ $\rightarrow$ 3s$^1$3p$^6$4p $\leftrightarrow$ 3s$^2$3p$^5$ $\varepsilon \ell$, $\ell$=s,d Fano window resonance. An interferometric technique using an attosecond pulse train, i.e. a frequency comb in the extreme ultraviolet range, and a weak infrared probe field allows us to study both amplitude and phase of the photoionization probability amplitude as a function of photon energy. A theoretical calculation of the ionization process accounting for several continuum channels and bandwidth effects reproduces well the experimental observations and shows that the phase variation of the resonant two-photon amplitude depends on the interaction between the channels involved in the autoionization process.