Below threshold nonsequential double ionization with linearly polarized two-color fields II: Quantum interference

We perform a systematic analysis of intra-channel quantum interference in laser-induced nonsequential double ionization with linearly polarized bichromatic fields, focusing on the recollision-excitation with subsequent ionization (RESI) mechanism, and employing the strong-field approximation. We generalize and elaborate several analytic interference conditions for RESI in arbitrary driving fields, with a focus on the interference arising from the specific symmetries of bichromatic fields. For example, for waves of comparable strengths, multiple events per half cycle for the direct electron must be considered. Furthermore, interference breaks some of the symmetries arising from the field. We detangle the superimposed interference fringes originating from phase differences related to symmetrization due to electron exchange, temporal shifts and a combination of exchange and event interference. We show that the hierarchy between exchange-only and exchange-temporal interference is fluid and can be manipulated by an appropriate choice of driving-field parameters. This is enabled by different types of interference occupying specific regions of the plane spanned by the electron momentum components parallel to the driving-field polarization.