RIKEN/SPring-8, Kouto 1-1-1, Sayo, Hyogo 679-5148, Japan.
Phys Rev Lett. 2011 Nov 4;107(19):193603. doi: 10.1103/PhysRevLett.107.193603. Epub 2011 Nov 1.
We have observed and characterized 501.6 nm collective spontaneous emission (superfluorescence) following 1s(2) → 1s3p excitation of helium atoms by 53.7 nm free-electron laser radiation. Emitted pulse energies of up to 100 nJ are observed, corresponding to a photon number conversion efficiency of up to 10%. We observe the peak intensity to scale as ρ(2) and the emitted pulse width and delay to scale as ρ(-1), where ρ is the atom number density. Emitted pulses as short as 1 ps are observed, which corresponds to a rate around 75,000 times faster than the spontaneous 1s3p → 1s2s decay rate. To our knowledge, this is the first observation of superfluorescence following pumping in the extreme ultraviolet wavelength region, and extension of the technique to the generation of extreme ultraviolet and x-ray superfluorescence pulses should be straightforward by using suitable atomic systems and pump wavelengths.
我们观察并描述了氦原子通过 53.7nm 自由电子激光辐射的 1s(2)→1s3p 激发后产生的 501.6nm 集体自发发射（超荧光）。观察到的发射脉冲能量高达 100nJ，相应的光子数转换效率高达 10%。我们观察到峰值强度与 ρ(2)成正比，发射脉冲宽度和延迟与 ρ(-1)成正比，其中 ρ 是原子数密度。观察到最短的脉冲持续时间为 1ps，这对应于比自发 1s3p→1s2s 衰减率快约 75000 倍的速率。据我们所知，这是首次在极紫外波长区域泵浦后观察到超荧光，并且通过使用合适的原子系统和泵浦波长，该技术应该可以很容易地扩展到产生极紫外和 X 射线超荧光脉冲。
