Multiple-wavelength superfluorescence in helium following FEL excitation; Ultrafast experiments and simulations

Harries, J.; Ohae, Chiaki*; Iwayama, Hiroshi*; Kawaguchi, Kentaro*; Kuma, Susumu*; Miyamoto, Yuki*; Nagasono, Mitsuru*; Nakajima, Kyo*; Yabashi, Itsuo*; Shigemasa, Eiji*; Sasao, Noboru*; Togashi, Tadashi*; Uetake, Satoshi*; Wakabayashi, Tomonari*; Yoshimi, Akihiro*; Yoshimura, Koji*; Yoshimura, Motohiko*

Superfluorescence is the rapid, collective emission of radiation following the ultrafast creation of a population inversion in an atomic medium. We report the results of experiments and simulations for the excitation of helium atoms using pulses from the SCSS EUV free-electron laser.