Emission of Thermally Activated Electrons from Rare Gas Clusters Irradiated with Intense VUV Light Pulses from a Free Electron Laser

Abstract

The ionization dynamics of Ar and Xe clusters irradiated with intense vacuum ultraviolet light from a free-electron laser is investigated using photoelectron spectroscopy. Clusters comprising between 70 and 900 atoms were irradiated with femtosecond pulses at 95 nm wavelength (approximately 13 eV photon energy) and a peak intensity of approximately 4 x 10(12) W/cm2. A broad thermal distribution of emitted electrons from clusters with a maximum kinetic energy up to 30-40 eV is observed. The observation of relatively low-energy photoelectrons is in good agreement with calculations using a time-dependent Thomas-Fermi model and gives experimental evidence of an outer ionization process of the clusters, due to delayed thermoelectronic emission.

Interaction of intense vuv radiation with large xenon clusters

“…The largest discrepancy between our calculated spectrum and the spectrum from [37] occurs at low ejection energy. In addition, our model of the cluster expansion predicts that the majority of electrons will comprise electron plasmas which remain bound to the cluster ions and become quite cold during the process of expansion.…”

“…A recent experiment [37] has for the first time measured the energy spectrum for electrons emitted from rare gas clusters exposed to intense VUV light. They give ejection spectra for 70 atom xenon clusters exposed to a 4.4 × 10 12 W/cm 2 pulse of VUV light at the same photon energy as the original Hamburg experiment, finding an electron distribution which decreases approximately exponentially according to I = I 0 exp (−E kin /E 0 ), with E 0 = 8.9 eV.…”

Heterogeneous clusters as a model system for the study of ionization dynamics within tampered samples

“…In this study we consider heterogeneous clusters composed of the noble gas atoms Xe and Ar, which have been extensively studied experimentally [1][2][3][4][6][7][8][9][10]. Using a fully nonequilibrium kinetic equation code (i.e., the Boltzmann solver described in [26,30,31]), we will demonstrate the significant effect of cluster composition on the ionization dynamics.…”

“…Their physical properties put them on the border between solid state and gas phase. Clusters are excellent objects to test the dynamics of samples irradiated with shortwavelength radiation from free-electron lasers (FELs) [1][2][3][4][5][6][7][8][9][10] and from high-harmonic-generation sources [11]. By studying the dependence of the cluster response on the cluster size, the influence of the atomic and condensed-matter effects on the ionization dynamics can be explored.…”

Next generation advanced light source science

“…These experiments will be technically very demanding, requiring some years of development after the hard X-ray FELs become available, but the information they yield will be enormously valuable in biology, where the majority of proteins (for example) cannot be crystallised. The high energy and high fluence of the pulses from the X-ray FELs will result in the molecule or cluster under study being destroyed by undergoing a 'Coulomb explosion' and turning into a plasma on timescales of tens of fs [3,21,22]. The experiment is thus intrinsically a 'one-shot' experiment, and data must be gathered from an individual molecule before it is destroyed, requiring fast detection and data readout.…”