Molecular internal dynamics studied by quantum path interferences in high order harmonic generation

Highlights: ► Electronic trajectories in high order harmonic generation encodes attosecond and femtosecond molecular dynamical information. ► The observation of these quantum paths allows us to follow nuclear motion after ionization. ► Quantum paths interference encodes a signature of superposition of ionization channels. ► Quantum paths interference encodes a signature of transfer of population between channels due to laser coupling. ► Quantum paths interference is a promising technique to resolve ultra-fast dynamical processes after ionization. - Abstract: We investigate how short and long electron trajectory contributions to high harmonic emission and their interferences give access to information about intra-molecular dynamics. In the case of unaligned molecules, we show experimental evidence that the long trajectory contribution is more dependent upon the molecular species than the short one, providing a high sensitivity to cation nuclear dynamics from 100's of as to a few fs after ionisation. Using theoretical approaches based on the strong field approximation and numerical integration of the time dependent Schrödinger equation, we examine how quantum path interferences encode electronic motion when the molecules are aligned. We show that the interferences are dependent upon which ionisation channels are involved and any superposition between them. In particular, quantum path interferences can encode signatures of electron dynamics if the laser field drives a coupling between the channels. Hence, molecular quantum path interferences are a promising method for attosecond spectroscopy, allowing the resolution of ultra-fast charge migration in molecules after ionisation in a self-referenced manner