Bulletin of the American Physical Society
2005 36th Meeting of the Division of Atomic, Molecular and Optical Physics
Tuesday–Saturday, May 17–21, 2005; Lincoln, Nebraska
Session L2: Synchrotron Radiation and Novel Photon Sources |
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Chair: Nora Berrah, Western Michigan University Room: Burnham Yates Conference Center Ballroom II |
Friday, May 20, 2005 1:30PM - 2:06PM |
L2.00001: Obtaining the complex correlation functions of photo-double ionization in helium Invited Speaker: The three particle breakup in photo-double ionization of helium, in dipole approximation, is fully characterized by two complex correlation functions. I will present a method to obtain these functions from experiment. The method is particularly well suited for experiments with $4\pi$ imaging of the two emitted photoelectrons, or of one electron and the recoiling photoion, as in COLTRIMS experiments. With unpolarized light or linearly polarized radiation one obtains the absolute magnitudes of the two correlation functions and the cosine of their relative complex phase. From these quantities one can deduce all observables in this process except for the direction of the circular dichroism or any spin-related observables. With a circular component in the incoming radiation one also obtains the sine of the relative phase and the degree of circular polarization. I will also discuss the effect of nondipolar corrections and the prospects of obtaining information on the three additional correlation functions originating from quadrupolar contributions in the interaction. [Preview Abstract] |
Friday, May 20, 2005 2:06PM - 2:42PM |
L2.00002: Clusters in XUV Radiation Fields Invited Speaker: The behavior of weakly bound clusters exposed to XUV radiation in two different regimes of intensity is discussed. At the intensities currently provided by synchrotron radiation sources, only one-photon absorption plays a role. A cluster is singly ionized and a hole in the valence shell is formed. In atoms and small molecules, an inner valence hole is electronically stable, but in clusters an ultrafast, Auger-like decay process can occur. This process, referred to as Interatomic Coulombic Decay (ICD), is characterized by an efficient Coulombic energy transfer mechanism between monomers in the cluster. The talk provides a basic overview of the phenomenon of ICD. The most important theoretical predictions are presented, together with recent experimental evidence for ICD in neon clusters. In the second part of the talk, motivated by a recent experiment using the new free-electron laser at DESY in Hamburg, the interaction of xenon clusters with intense VUV radiation is analyzed. In the experiment, xenon clusters were found to absorb a very large number of VUV photons, many more than had been anticipated---based on the experience with long-wavelength lasers. The theoretical description developed accounts for the experimental observation. Key aspects are the rapid formation of a dense nanoplasma and the efficiency of photon absorption in electron--ion collisions, a process known as Inverse Bremsstrahlung. [Preview Abstract] |
Friday, May 20, 2005 2:42PM - 3:18PM |
L2.00003: Photoelectron Spectroscopy of Rare Gas Clusters Using Synchrotron Radiation Invited Speaker: Clusters of atoms and molecules occupy an intermediate state of matter between gaseous and condensed phases and offer unique opportunities to study the effects of condensation on the electronic spectroscopy of matter in a controlled manner. The evolution of atomic and molecular orbitals into the electronic bands exhibited by solids can be examined as a function of cluster size using photoelectron spectroscopy, for example. A program to investigate the photoionization of clusters using synchrotron radiation has begun at the Advanced Light Source synchrotron at Lawrence Berkeley National Laboratory. A skimmed continuous supersonic beam source has been adapted to three existing photoelectron spectrometers; 1) a high resolution hemispherical analyzer, 2) a pair of high resolution time-of-flight (TOF) electron spectrometers, and 3) an electron spin sensitive Mott-TOF spectrometer [1]. Results from each of the three instruments will be discussed. Utilizing circularly polarized synchrotron radiation, we have studied the spin polarization of the Xe 4d photolines of large Xe clusters using the Mott-TOF spectrometer. Previous studies of the angular distributions of Xe 4d photoelectrons from these clusters identified a reduced anisotropy in the electron emission that was attributed to elastic scattering of photoelectrons by surrounding atoms in the cluster [2]. To further investigate this hypothesis we have used our spin-TOF spectrometer to measure the effect of clustering on the spin polarization of the electrons. Spin polarization measurements will be shown which show a reduced polarization for electrons emerging from the inner part of the cluster, supporting the proposed model of elastic scattering. \underline {References:} [1] N. Berrah \textit{et al.}, J. Electron Spectrosc. Relat. Phenom. \textbf{101}, 1 (1999). [2] G. \"{O}hrwall \textit{et al}., J. Phys. B \textbf{36}, 3937 (2003). [Preview Abstract] |
Friday, May 20, 2005 3:18PM - 3:54PM |
L2.00004: LCLS, a 1.5 Angstrom Free Electron Laser: Opportunities and Challenges Invited Speaker: The dream of a laser operating at hard x-ray wavelengths is about to be realized. The Linac Coherent Light Source will be the world's first hard x-ray free electron laser reaching 1.5 Angstroms in the fundamental. The scientific opportunities span the breadth of science studied today with photons and extends the photon matter interactions into unchartered regimes with unprecedented fields at Angstrom wavelengths. Along with these opportunities come technical challenges. The background, performance and opportunities for the LCLS will be described. The technical challenges will be highlighted and the status of their solutions will be discussed. Finally, as with other accelerator based light sources even before the first saturated 1.5 Angstrom beam has been produced ideas for shorter pulses, higher energies and variable polarization are being discussed. These `future' options will be highlighted. [Preview Abstract] |
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