Atomic and molecular photophysics using short-wavelength free-electron laser (FEL). Multiphoton ionization and deexcitation of rare gas clusters using extreme ultraviolet FEL light

The cluster where several atoms to several tens of thousands of atoms aggregate shows the behaviors greatly different from isolated atoms in the interaction with high-intensity free-electron laser (FEL) beams. This paper introduces the main findings obtained from the authors' cluster experiments at the SPring-8 Compact SASE Source test accelerator. In the cluster where constituent atoms are aggregated at almost the same atomic density as the bulk, the following can be inferred from the experiment: Multi-photon absorption occurs easily, and in addition, interesting state has been realized such as the generation of nanoplasma due to the interaction between a number of generated electrons and ions. This paper mainly discusses the process of ionization of the cluster through irradiation of the extreme ultraviolet FEL and the behaviors of the generated charge. (A.O.)