Strong-field photoionization of a mid-infrared wavelength

Increasing the driving laser wavelength into a region above 1 μm has lead to a number of interesting phenomena and applications in the field strong-field interactions1 of atoms such as the of the discovery of low-energy structures or the generation or high harmonics with photon energies above 1 keV. Due to the nuclear degree of freedom, strong-field photoionization of small molecules induces more complex dynamics such as charge-resonant enhanced ionization, or laser-induced electron diffraction. Here, the fragmentation of an ion beam by a strong mid-infrared laser field is studied experimentally as a function of intensity. Three-dimensional coincidence imaging in combination with a well collimated ion beam and high pondermotive potential of the laser allows to perform a kinematically complete experiment where the momentum of the two protons, and, are measured directly and the electron momentum,, is inferred based on momentum conservation. The experimental results s
how a double-peak structure in the kinetic energy release (KER) spectrum that indicates a strong dependence of the ionization yield on the inter-nuclear separation,. It is found that this structure is very sensitive to the intensity. 2D-plots of the ionization yield as function of KER show that the energy-dependent electron yield is sensitive to energy of the two nuclei. Solutions of the time-dependent Schrödinger equation in one and two dimensions are used in order to gain insight into the physical mechanisms.