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

The delay in the one-photon ionization of atoms is encoded in the photoionization-amplitude phase [1]. A well established technique to recover this phase is the Reconstruction of Attosecond Beating By Interference of Two-photon Transitions (RABBITT), which utilizes an attosecond pulse train (APT) pump in association with an IR probe pulse with controllable delay [2]. In RABBITT, the phase difference between the photoelectron amplitudes generated by consecutive odd harmonics is inferred from the interference of their common sideband, based on assumptions on the continuum-continuum (cc) radiative-transitions delay [3]. Angularly-resolved measurements can give access to the angular dependence of the time delay [4] as well as to the delay for the emission of photoelectrons with different orbital angular momenta [5]. By measuring also the beatings between two-photon and one-photon paths, it is possible to circumvent the need of using analytical values for the cc delay [6].  In this work, we present a numerical analysis of an alternative method to extract both one-photon and two-photon amplitudes for a given atomic target. The method combines data from two angularly resolved RABBITT measurements that employ the same APT and either the fundamental or the second harmonic of the IR pulse as a probe. Using Monte Carlo simulations, we determine the range of all the relevant one-photon and two photon amplitudes that are compatible with the baseline, amplitude and phase of the asymmetry parameters of both harmonic and sideband signals, measured with realistic uncertainties. This approach offers a novel pathway for disentangling complex photoionization dynamics.

[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)