Floquet interpretation of attosecond RABBITT traces

Originally proposed for the temporal characterization of train of attosecond pulses, the reconstruction of attosecond beating by interference of two-photon transitions (RABBITT), has become a wide-spread, powerful technique, capable of capturing ultrafast electron dynamics through an interferometric approach. Starting from the well-known strong-field approximation (SFA) description of a two-color photoelectron spectrum, here we develop a model that interprets a RABBITT trace as the interference of different Floquet ladder states generated in the continuum by a femtosecond infrared (IR) pulse after ionization by the attosecond radiation. In turn, this allowed us to develop an analytical model capable of predicting the amplitude and phase of the oscillating sidebands and main bands while including the effect of nonstandard interference paths and, in first approximation, of the finite IR pulse envelope. Our results thus suggest a way to extend the RABBITT model to higher intensities and beating frequencies, and disentangle different oscillating signals in a congested photoelectron spectrogram as the one associated with molecular targets.