Numerical analysis of spectrograms in attosecond photoionisation
Since their first observation in the early 2000s, attosecond light pulses (1 as = 10^-18s) in the extreme ultraviolet (XUV) range have revolutionized the study of electron dynamics in atoms and molecules. Attosecond spectroscopy based on laser-dressed photoionisation has made it possible to observe ultrafast processes such as time delays in the photoelectric effect. This approach consists in measuring the kinetic energy of photoelectrons released through the ionization of atoms or molecules by an attosecond pulse combined with a laser pulse. Although the released photoelectron behaves as a quantum wavepacket, its coherence is often degraded for both instrumental and quantum-mechanical reasons.
The goal of this work is to develop and apply computational tools to extract decoherence information, in the form of an electron density matrix, from photoelectron kinetic energy spectra. In that perspective, it is crucial to evaluate the reliability of these numerical tools. Therefore, we have performed a theoretical study in order to identify the ambiguities and artefacts that can arise in the reconstruction process and to find ways to manage them.
We have then analyzed experimental spectrograms previously obtained through the ionization of neon atoms. This study allowed us to confirm quantitatively the origin of the instrumental decoherence observed so far in these experiments. Finally, we have for the first time reconstructed a photoelectron density matrix obtained by the ionization of both the 2s and 2p shells of neon.