Cascade and competitive superfluorescence in He studied at the EUV free-electron laser SCSS using a streak camera

Harries, J.; Iwayama, Hiroshi*; Nagasono, Mitsuru*; Togashi, Tadashi*; Kuma, Susumu*; Nakajima, Kyo*; Shigemasa, Eiji*

Following excitation of 1s3p atoms in a sample of pressures around 3000 Pa the dominant mode of decay was found to be superfluorescence at 501.6 nm. At higher densities superfluorescence on other transitions, 3d-2p at 667.8 nm and 3s-2p at 728.1 nm was also observed. Using filters in front of a streak camera, we have characterized this competitive process. Further, we have studied excitation at 52.2 nm, corresponding to 1s4p excitation. Emission at 667.8 nm emission was found to be dominant, indicating two-step cascade superfluorescence 4p-3d-2p.