| The interaction of rare gas clusters with intense vacuum ultraviolet radiation from the DESY free electron lasers has yielded many surprising results. In first experiments performed with 100 nm radiation unexpected high energy absorption was measured. The clusters disintegrated in a strong coulomb explosion with ion kinetic energies in the keV rang and thermionic electron emission was observed. These results indicate that for clusters in intense laser fields down to 100 nm and intensities up to 1013 W/cm2 very efficient energy absorption mechanisms involving plasma heating processes exist and new theoretical explanations were suggested. In fall 2005 the DESY FLASH FEL became operational delivering radiation down to first 32 and later also 13 nm wavelengths with intensities up to 10exp14 W/cm2. We have performed first experiments with a combined time-of-flight spectroscopy and imaging approach. The new data give evidence that the dominant physical drivers in the light %G–%@ matter interaction at these reduced wavelength change and plasma type absorption is only of minor importance. At 32 nm the ionic fragments from the exploding clusters are ejected with only 25 eV and the electrons are emitted from the cluster in a multistep photemission process. The atoms within the cluster move by only 3 Angstrom during the pulse duration making imaging experiments possible. At 13 nm wavelength first experiments about the ionization dynamics including core levels could be performed with Xe clusters. All results will be discussed and compared to theoretical prediction. |
|