Multichannel photoelectron phase lag across atomic barium autoionizing resonances

Phase lag associated with coherent control where an excited system decays into more than one product channel has been subjected to numerous investigations. 

Although previous theoretical studies have treated the phase lag across resonances in model calculations, the quantitative agreement has never been achieved between the theoretical model and experimental measurement of the phase lag from the ω-2ω ionization of atomic barium. Yamazaki and Elliot, PhysRevLett.98.053001(2007), PhysRevA.76.053401(2007), suggest that a toy model with phenomenological parameters is inadequate to describe the observed phase lag behavior. 

Here the phase lag is treated quantitatively in a multichannel coupling formulation, and our calculation based on a multichannel quantum defect and R-matrix treatment achieves good agreement with the experimental observations. Our treatment also develops formulas to describe the effects of hyperfine depolarization on multiphoton ionization processes.  Moreover, we identify resonances between Ba⁺ 5d_3/2 and 5d_5/2 thresholds that have apparently never been experimentally observed and classified. This work has been published as Phys. Rev. A. 105, 013113 (2022).