Resonant multiphoton processes in the soft-x-ray regime

Abstract

The multiphoton ionization of neon atoms was studied in the focus of the soft-x-ray free-electron laser FLASH by photoion spectroscopy. The photon energy was chosen in the range of ${\text{Ne}}^{+}\text{ }2p\ensuremath{\rightarrow}n\ensuremath{\ell}$ resonances between 41 and 42 eV. The experiments were performed at the PG0 branch of the FLASH monochromator beamline while measuring the spectral distribution of every single FLASH pulse. By correlating the ratio of doubly and singly charged neon ions generated and the measured photon energy distribution, the enhancement of this ratio due to resonant ${\text{Ne}}^{+}$ excitation was found.