Simultaneous measurements of superradiance at multiple wavelength from helium excited states, 2; Analysis

励起状態ヘリウム原子から複数波長の超放射の同時観測,2; 解析

大饗 千彰*; Harries, J.; 岩山 洋士*; 川口 健太郎*; 久間 晋*; 宮本 祐樹*; 永園 充*; 中嶋 享*; 中野 逸夫*; 繁政 英治*; 笹尾 登*; 植竹 智*; 若林 知成*; 吉見 彰洋*; 吉村 浩司*; 吉村 太彦*

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

Previous experimental studies of superradiance (SR) in multi-level systems have been explainable using the predictions of the well-known simple two-level SR model. However our recent study using EUV free-electron laser excitation of helium atoms, where SR was observed at wavelengths of 502 nm, 668 nm, and 728 nm, revealed behaviour which necessitates a full multi-level treatment of the SR development. In this paper, we report simulations of the initial excitation by the FEL pulses, and the subsequent development of multi-level SR. The results of the simulation reproduce the experimental findings, and reveal that competitive SR on two transitions with a common upper level plays an important role in the development of the system.