Probing strong-field photoionization of atoms and diatomic molecules with short-wave infrared radiation
The investigation of the interaction between atoms and diatomic molecules with strong laser fields with peak intensities in the range between ?10?^12 and ?10?^16 W/cm^2 has revealed fascinating phenomena such as high energy above-threshold ionization (HATI), non-sequential ionization (NSDI), high-harmonic generation (HHG) and frustrated tunnel ionization (FTI). Although experimental and theoretical considerations have shown that using longer laser wavelength is interesting from several aspects, the majority of measurements has been performed at laser wavelengths below 1.0 m. Here, a laser source of intense femtosecond laser pulses with short-wave infrared (SWIR) wavelength is put to operation and applied to investigate strong-field photoionization (SFI) of atoms and diatomic molecules using two different experimental techniques for momentum spectroscopy of laser-induced fragmentation processes. Momentum distributions from strong-field photoionization of Xenon with different pulse duration are measured using the velocity map imaging technique. Besides observation of the pulse duration dependence a low-energy feature is investigated in detail. The corresponding modeling shows that the observations can be traced to rescattering between the laser-driven photoelectron and the remaining ion. SFI of the hydrogen molecular ion, H_2^+ (H_2^+?H^++H^++e^-), is investigated using Ion Target Recoil Ion Momentum Spectroscopy (ITRIMS). Besides measuring intensity dependent vector momentum distributions it is shown that momentum conservation can be used to extract the correlated electron momentum from the measured data, although the electron is not detected. This enables the analysis of the correlated electron-nuclear momentum distribution. Together, with a one-dimensional two-level model, this sheds light on correlated electron-nuclear ionization dynamics during SFI of diatomic molecules by SWIR fields.