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TUOEI01 |
FEL Experiments for Atoms and Atomic Clusters: From EUV to X Rays | |
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Following FLASH operation in Germany [1], SPring-8 Compact SASE Source (SCSS) test accelerator in Japan [2] started user operation in 2008. These facilities provide EUVFEL pulses. In 2009, LCLS [3] started user operation providing the soft X-ray FEL pulses. Now it provides users with hard X-ray FEL pulses. SACLA, Japanese XFEL, lased in June 2011 in the hard X-ray regime and started user operation in March 2012. We have been studying multi-photon processes in atoms, molecules, and clusters at these FEL facilities, from EUV to X-rays, using electron and ion momentum spectroscopy [4-14]. I will describe some showcase examples at the conference, to illustrate how we users enjoy new opportunities to investigate unexplored new areas of science using these new light sources. First, I will discuss two examples for a few photon processes in atoms. The first example is the simplest nonlinear process, i.e., two photon single ionization of helium atoms by the EUV pulses at SCSS. Here, I will demonstrate that intense ultrashort pulses can be used to control the quantum processes [15]. The second example is a few photon absorption of xenon atoms by the X ray pulses at SACLA, where I will demonstrate that the xenon atom can absorb up to 4 photons in the x-ray regime of 5-5.5 keV. Second, I will discuss multi-photon processes in rare-gas atomic clusters. Namely, after frustration of the cluster photoionization and Auger decay by the increase of the ionization potential, the cluster still absorbs photons and forms nanoplasma. Then thermal emission takes place and then coulomb explosion and recombination take place. I will describe the fate of the multiply excited nanoclusters based on our ion and electron spectroscopy data both in the EUV and X-ray regimes. I am grateful to all the collaborators who are co-authors of Refs. [4-15] and who are on SACLA campaigns. The work is supported by X-ray Free Electron Laser Utilization Research Project of MEXT.
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