Spectroscopic studies of neutral otoms in and on superfluid helium

中性原子注入到液氦中会产生类似气泡的氦结构，由于泡利不相容原理，这种杂质原子在自产生的气泡中的模型被称为原子气泡模型。现已知，该模型很好地解释了观测光谱的一般特征。在目前的工作中，我们特别关注了这个模型不能解释的现象。对于基态碱原子，我们观察到激发D2光谱的分裂，这是由于零点涨落引起的四极振荡所致。对于被激发的碱原子，观察到了一些新的红外光谱，这些光谱明显偏离了D线。与计算的绝热势进行比较，我们发现这些红外线来自于被激发的碱原子上附着着几个氦原子的分子或团簇。此外，还研究了Tm原子注入液态氦和固态氦的情况。基态和低激发态之间的光学跃迁是由于内核电子的光学跃迁。存在两个外层电子，预计它们会屏蔽周围的氦。我们可以成功地观察到Tm原子的几次跃迁，由于这种屏蔽，内核的跃迁非常尖锐。我们成功地观察到了两个精细结构能级之间的弱磁偶极子跃迁，并精确地测量了上亚稳态的寿命。我们还研究了气态碱原子与液氦表面的相互作用。表面的结合能很低，因此相互作用大多是排斥的，利用涂覆在细胞壁上的液氦薄膜作为原子反射器，我们首次实现了在液氦温度下的长寿命碱蒸气电池。利用光泵浦技术可以获得近乎完美的电池中碱原子的自旋极化。

A neutral atom implanted into liquid helium produces a bubble-like structure of helium, pushing out the surrounding helium due to the Pauli exclusion principle, This model of impurity atom in a self-produced bubble is called atomic bubble model. It is now known that this model explains well the general features of observed spectra. In the present work, we have focused particularly on the phenomena which cannot be explained by this model. For the ground state alkali atom, we observed the splitting of the exciting D2 spectra, which were found to be due to quadrupole oscillations caused by zero-point fluctuation. For the excited alkali atom, some new infrared spectra were observed, which were shifted considerably from the D lines. Comparing with calculated adiabatic potentials, we found that these lines infrared lines were from the molecules or clusters with several helium atoms sticking to the excited alkali atom. The Tm atoms implanted into liquid and solid helium were also studied. The optical transitions between the ground and the lower-lying states are due to those of the inner core electrons. There exist two outer electrons, which are expected to shield surrounding helium. We could succeed to observe several transitions of Tm atoms, the inner core transitions being extremely sharp due to this shielding. We succeeded to observe a weak magnetic dipole transition between two fine-structure levels and to measure precisely the lifetime of the upper metastable state. We have also studied gaseous alkali atoms interaction with the surface of liquid helium. The binding energy on the surface is very low and hence the interaction is mostly repulsive, Using the liquid helium film coated on the cell walls as an atomic reflector, we could realize, for the first time, a long-lived alkali vapor cell at a liquid helium temperature. Almost perfect spinpolarization of alkali atoms in the cell could be attained by using optical pumping techniques.