Angle-Dependent Continuum Transitions in Multi-Sideband RABBITT on Argon: Experiment and Theory*

The reconstruction of attosecond beating by interference of two-photon transitions (RABBITT) [1,2] is a commonly used technique for the study of photoionization dynamics in atomic, molecular, and solid systems with attosecond pulses [3]. Recently, a three-sideband (3-SB) scheme was suggested [4] and analyzed in detail theoretically for atomic hydrogen [5]. We present recently obtained results from a 3-SB RABBITT experiment with argon as the target gas. The dependence of the continuum-continuum transition phase on the orbital angular momenta of the continuum states is revealed in the angular variation of the three sideband phases. We also directly show an effect of Fano resonances on these phases. Argon is experimentally more readily accessible than atomic hydrogen, but its multi-electron character presents a major challenge to theory. Since single-active electron (SAE) calculations do not adequately reproduce the photoionization cross section of argon, we use the multi-electron R-matrix with time dependence (RMT) method [6] to generate theoretical predictions. These are compared with the latest experimental data.

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[5] D. Bharti et al., Phys. Rev. A 103 (2021) 022834.

[6] A. C. Brown et al., Comput. Phys. Comm. 250 (2020) 107062.