The RABBITT technique enables precise extraction of amplitude and phase information from photoelectron spectra but is traditionally limited to weak IR fields and two-photon pathways. We present RABBITT-HOP, demonstrating how Higher-Order Processes can be identified even at moderate IR intensities. We target the 1s4p and 1s5p states in He, and show how these resonances imprint in multiple, higher-lying sidebands and mainbands.
Roantree et al. (Tue,) studied this question.