Auböck Gerald, Nagl Johann, Callegari Carlo, Ernst Wolfgang E
Institute of Experimental Physics, TU Graz, Petersgasse 16, 8010 Graz, Austria, EU.
Phys Rev Lett. 2008 Jul 18;101(3):035301. doi: 10.1103/PhysRevLett.101.035301. Epub 2008 Jul 14.
We measured laser-induced-fluorescence (LIF) and beam-depletion (BD) spectra of rubidium atoms (5S-5P transition) on the surface of superfluid helium nanodroplets (M-He_{N} with M=Rb). It is known that when M is a lighter alkali atom electronic excitation always leads to detachment of the excited atom (M;{}). The dissociation energy, few tens cm;{-1}, comes either as photon excess energy or from the barrierless formation of a M;{}-He exciplex. We observe that this picture does not hold when M=Rb and the photon excess energy is small: we are able to excite atoms without detaching them from the droplet, thanks to a barrier preventing formation of the exciplex. This system is ideally suited for optical spin pumping in a He nanodroplet, whose achievement we explicitly demonstrate in a pump-probe magnetic circular dichroism experiment.
我们测量了超流氦纳米液滴（M-Heₙ，其中M = Rb）表面铷原子（5S - 5P跃迁）的激光诱导荧光（LIF）和光束耗尽（BD）光谱。已知当M为较轻的碱金属原子时，电子激发总会导致激发原子（M*）的脱离。解离能为几十厘米⁻¹，它要么作为光子过剩能量，要么来自无势垒形成的M* - He激基复合物。我们观察到当M = Rb且光子过剩能量较小时，这种情况并不成立：由于存在阻止激基复合物形成的势垒，我们能够激发原子而不使其从液滴上脱离。该系统非常适合在氦纳米液滴中进行光学自旋泵浦，我们在泵浦 - 探测磁圆二色性实验中明确展示了这一成果。
