R-matrix with time-dependence calculations for three-sideband RABBITT in helium

Following up on a recent paper (Bharti et al. in Phys Rev A 109:023110, 2024), we compare the predictions from several R-matrix with time-dependence calculations for a modified three-sideband version of the “reconstruction of attosecond beating by interference of two-photon transitions” (RABBITT) configuration applied to helium. Except for the special case of the threshold sideband, which appears to be very sensitive to the details of coupling to the bound Rydberg states, increasing the number of coupled states in the close-coupling expansion used to describe the ejected-electron–residual-ion interaction hardly changes the results. Consequently, the remaining discrepancies between the experimental data and the theoretical predictions are likely due to uncertainties in the experimental parameters, particularly the detailed knowledge of the laser pulse.