Extended Data Fig. 4: Influence of two-photon ionization via nearby states.
From: Strong-field quantum control in the extreme ultraviolet ___domain using pulse shaping
Calculated photoelectron spectra for resonant driving (pulse duration: 52.6 fs, GDD = 0 fs2) for three different peak intensities (as labelled). Blue: full TDSE-SAE model including all relevant He states. Red: suppressing two-photon ionization pathways via near-resonant states except for the 1s2p state. The latter case eliminates interference of multiple photoionization paths. The strong similarity between both photoelectron spectra confirms that photoionization paths via states energetically close to the 1s2p state play a negligible role. In particular, both spectra exhibit a clear asymmetry between the upper/lower AT states for a range of FEL intensities.
