ECAMP 15

Traditionally, photoionization studies have been carried out in the frequency domain by measuring the cross-section and angular distributions of photoelectrons. Newly developed laser assisted interferometric techniques expand these studies into the time domain thus marking the advent of attosecond science [1]. Here we show that the attosecond time delay, also known as the Wigner time delay [2], can be retrieved from the photoionization cross-section by way of the logarithmic Hilbert transform (LHT). The LHT can be used to relate the cross-section and time delay in a large number of single-photon resonant ionization processes. It provides a good estimate of time delay near atomic and molecular shape resonances [3], confinement resonances in the endohedrally trapped Xe@C$_{60}$ and the Cooper minima in the valence shells of noble gas atoms [4]. Fano resonances can also be treated in the similar way. Particularly interesting is application of the LHT to two-photon XUV+IR ionization where the Fano resonance appears in one of the two interfering channels of the RABBITT process [5].
[1] P.B. Corkum and F. Krausz, Nat. Phys. \href{https://www.nature.com/articles/nphys620}{\textbf{3}, 381 (2007)}.
[2] A.S. Kheifets, J. Phys. B \href{https://iopscience.iop.org/article/10.1088/1361-6455/acb188}{\textbf{ 56}, 022001 (2023)}
[3] A.S. Kheifets and S. Catsamas, Phys. Rev. A \href{https://journals.aps.org/pra/abstract/10.1103/PhysRevA.107.L021102}{ \textbf{107} , L021102 (2023)}
[4] Jia-Bao Ji \emph{et al.}, New J. Phys. \href{https://iopscience.iop.org/article/10.1088/1367-2630/ad7633}{ \textbf{26} , 093014 (2024)}
[5] A.S. Kheifets, arXiv preprint \href{https://arxiv.org/abs/2410.16696}{ 2410.16696 (2024)}