Self-referenced interferometric harmonic spectroscopy for coherent electron dynamics imaging and reconstruction of attosecond pulse trains

Motivated by recent advances in self-referenced interferometric harmonic spectroscopy [1], we theoretically investigate an alternative approach to attosecond transient absorption spectroscopy [2-3] (ATAS) and the RABBITT scheme [4] for electron dynamics imaging and attosecond pulse train (ATP) phase characterization. Specifically, the interferometric approach [1] relies on interference fringes measurements resulting from interference between ATP trains arriving from two spatially separated argon samples: a reference sample subject to an ATP, and the probe sample subject to a replica of the ATP and an infrared (IR) laser. The interference fringes changes as a function of the IR intensity.

In contrast to ATAS which gives access to the imaginary part of the refractive index through an absorption measurement, the interferometric technique of Ref. [1] gives information of its real part. Moreover, the narrow bandwidth centered around the central frequencies of the ATP allows to isolate the contributions from different target states to the refractive index as well as resolve the intertwined interference pathways being probed by a relatively weak delayed IR pulse. In analogy to the RABBITT scheme, changes in the ATP phases modify the relative phases of the different dynamical pathways and, therefore, our approach can be used for APT pulse characterization from the interference fringe measurements. Alternatively, the interference fringe measurements can be exploited to probe the underlying quantum dynamics, which is confirmed by an excellent agreement between third-order perturbation theory and the non-perturbative calculations. We incorporate macroscopic and field propagation effects by solving the Maxwell equations for the ATP and IR laser inside the samples in the scalar field approximation and beyond Beer’s law.