Momentum distributions from bichromatic ionization of atoms and molecules

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The response of atoms and molecules to intense laser pulses composed of two colours is investigated theoretically. In one part of the project, both colours are linearly polarized in orthogonal directions in order to probe the ionization dynamics induced by the fundamental field with a weak second harmonic field. In the other part, we choose both colours circularly polarized and counter-rotating in order to exploit the unusual mapping from ionization times to final electron momenta in such bicircular fields. Bircircular fields have recently found remarkable attention in the area of high-harmonic generation, but the photoelectron momentum distributions remained mostly unexplored. The momentum distributions are calculated by numerical solution of the time-dependent Schrödinger equation in order to capture both the direct and the rescattering electron trajectories. Comparisons are made with the strong-field approximation. In atoms, application of bicircular fields for the study of sub-cycle ionization dynamics is envisaged analogous to the attoclock method. In molecules, we analyse the orientation dependence of quantities relevant for strong-field processes such as ionization times and the lateral width of the momentum distributions. In the rescattering electron signal from molecules in bicircular fields, we search for the signature of electron diffraction to perform ultrafast imaging of molecular structure.