Near threshold two photon double ionization of Kr in the vacuum ultraviolet

We report angle resolved measurements on photoelectrons emitted upon near threshold two photon double ionization TPDI of Kr irradiated by free electron laser FEL pulses. These photoelectron angular distributions PADs are compared with the results of semirelativistic R matrix calculations. As reported by Augustin et al., it is found that the presence of autoionizing resonances within the bandwidth of the exciting FEL pulse strongly influences the PADs. In contrast to measurements on lower Z targets such as Ne and Ar, the larger spin orbit interaction, inherent in 4p subshell hole states of Kr, permits us to resolve and study PADs associated with some of the fine structure components of the Kr and Kr2 ion

Angle-resolved photoelectron spectroscopy of sequential three-photon triple ionization of neon at 90.5 eV photon energy

Multiple photoionization of neon atoms by a strong 13.7 nm (90.5 eV) laser pulse has been studied at the FLASH free electron laser in Hamburg. A velocity map imaging spectrometer was used to record angle-resolved photoelectron spectra on a single-shot basis. Analysis of the evolution of the spectra with the FEL pulse energy in combination with extensive theoretical calculations allows the ionization pathways that contribute to be assigned, revealing the occurrence of sequential three-photon triple ionization

Characterization of the FLASH XUV-FEL pulses by two-color photoionization experiments

The current key performance indicators of the pump-probe facility at the Free Electron Laser in Hamburg (FLASH) are described. The temporal and spatial characteristics of both the extreme ultra-violet (XUV) Free Electron Laser and the temporally synchronized optical femtosecond Ti:Sapphire laser are determined by measuring two-color above threshold ionization in rare gases. Characteristic sidebands appear in the photoelectron spectrum under the combined action of both radiation fields providing a very sensitive probe for the spatial and temporal overlap of both pulses. The high spatial acceptance of a magnetic bottle electron spectrometer enabled us to obtain single-shot photoelectron spectra and to correct for the inherent time jitter between both light sources, which reduces the temporal resolution when recording spectra in average mode. As an illustration of the first application, % of the pump-probe set-up, experimental results on polarization control in the two-photon two-color ionization of atomic He are presented