Reconstruction of one and two-photon atomic ionization amplitudes from multicolor RABBITT measurements*

The time delay in one-photon ionization of atoms is linked to the phase of the photoionization amplitude [1]. A well-known method to determine this phase is the Reconstruction of Attosecond Beating By Interference of Two-photon Transitions (RABBITT). This technique uses an attosecond pulse train (APT) as a pump and an infrared (IR) probe pulse with a controlled delay [2]. In RABBITT, the phase difference between photoelectrons produced by consecutive odd harmonics is extracted from their common sideband interference, assuming a known delay from continuum-continuum (cc) transitions [3]. Measuring photoelectrons at different angles provides insights into how the time delay depends on emission direction and angular momentum [4,5]. Additionally, studying the interference between one-photon and two-photon paths can help bypass the need for analytical cc delay values [6]. In this work, we explore a numerical approach to extract both one-photon and two-photon amplitudes for a given atom. Our method combines data from two angularly resolved RABBITT measurements, using the same APT with either the fundamental or second harmonic of the IR probe. Through Monte Carlo simulations, we determine the possible values of these amplitudes that match the observed asymmetry parameters of harmonics and sidebands, considering realistic uncertainties. This method provides a new way to analyze complex photoionization processes.

[1] R. Pazourek et.al., Rev. Mod. Phys. 87, 765 (2015).

[2] K. Kl¨under et.al., New J. Phys. 106 143002, 2011

[3] J. M. Dahlstr¨om et al., J. Phys. B: At. Mol. Opt. Phys. 45, 183001 (2012)

[4] S. Heuser, Phys. Rev. A 94, 063409 (2016)

[5] J. Peschel et.al., Nat. Comm. 13 5205, 2022

[6] J. Fuchs et.al., Optica 7 154, 2020