Probing Near-Threshold Electron Dynamics in Neon Using Attosecond Transient Absorption Spectroscopy

In recent work, we used a variant of the Reconstruction of Attosecond Beating by Interference of Two-photon Transitions (RABBITT) technique [1], Under-Threshold RABBITT (uRABBITT) [2], to study photoionization dynamics in neon atoms. We found that the threshold sideband, which is generated by interference between a bound- bound XUV + bound-free IR transition and a bound-free XUV + free-free IR transition, contained contributions from both the 2p⁵4d and 2p⁵6s states of neon, and that the nature of these contributions was heavily influenced by the XUV-IR delay in the laser pulse [3, 4]. In order to explore these dynmaics in more detail, we have performed Attosecond Transient Absorption Spectroscopy (ATAS) calculations using the R-Matrix with Time-dependence method [5]. ATAS is a powerful technique for studying the dynamics of the electron on its natural time scale, including near ionization thresholds [6]. In this presentation we will compare the results from our previous uRABBITT investigations with new ATAS calculations, and comment on any similarities and descrepancies in the infromation obtained from these techniques.

[1] P. Paul et al., Science 292 (2001) 1689

[2] D. M. Villeneuve, P. Hockett, M. J. J. Vrakking, and H. Niikura, Science 356 (2017) 6343

[3] M. Moioli, M. M. Popova et al., Phys. Rev. Research, accepted (2025)

[4] H. Mekuria et al., Bull. Am. Phys. Soc. (2024) K00.00042

[5] A. C. Brown et al., Comp. Phys. Commun. 250 (2020) 107062

[6] M. Wu et al., J. Phys. B: At. Mol. Opt. Phys. 49 (2016) 062003