Strong-field ionization of lithium

We report photoelectron energy spectra, momentum, and angular distributions for the strong-field single ionization of lithium by 30-fs laser pulses. For peak intensities between 10¹¹ and 10¹⁴ W/cm² at a central wavelength of 785 nm, the classical over-the-barrier intensity was reached well inside the multiphoton regime. The complete vector momenta of the ionization fragments were recorded by a reaction microscope with a magneto-optically trapped target (MOTREMI). On the theoretical side, the time-dependent Schr\"odinger equation was solved by two independent methods seeking the solution directly on a radial grid. Distinct differences between the results of both calculations and also in comparison with experiment point to a high sensitivity of this reaction with respect to small details, particularly in the description of the Li⁺ core.