Superfluorescence observed following EUV-FEL excitation of helium gas

気体ヘリウムのEUV自由電子レーザー励起に伴う超蛍光の観測

Harries, J.; 永園 充*; 岩山 洋士*; 富樫 格*; 登野 健介*; 矢橋 牧名*; 仙波 泰徳*; 大橋 治彦*; 石川 哲也*; 繁政 英治*

Harries, J.; Nagasono, Mitsuru*; Iwayama, Hiroshi*; Togashi, Tadashi*; Tono, Kensuke*; Yabashi, Makina*; Semba, Yasunori*; Ohashi, Haruhiko*; Ishikawa, Tetsuya*; Shigemasa, Eiji*

We are currently witnessing rapid progress in the extension of effects now commonplace with visible light lasers towards shorter and shorter wavelengths. Highlights include XFEL-pumped lasing, and electromagnetically-induced transparency. Superfluorescence shares similarities with ASE lasing, but occurs only if several specific conditions are met. We have observed and characterised superfluorescence at a wavelength of 501.7 nm following 1s1s1s3p excitation of helium atoms by 53.7 nm free-electron laser radiation. Emitted pulse energies of up to 100 nJ (10) photons were observed, corresponding to a photon number conversion efficiency of up to 10%. We observed the peak intensity to scale as , and the pulse width to scale as , where is the atom number density. Emitted pulses as short as 1 ps were observed.