MEASUREMENT OF CHARGE TRANSFER CROSS SECTION IN VERY LOW ENERGY REGION

在极低能量的射频离子阱中，成功地观察到了激光冷却镁离子和热钡原子之间的电荷转移过程。离子阱实验的优点是产生的离子也被捕获，并且具有很高的灵敏度。通过观察激光诱导的离子荧光，证实了钡离子的产生。截面估计为10^<-4> nm^2。这口井与参考文献（D. Rapp和W.E.Francis， J. Chem）中的理论计算值一致。物理学37,2631(1962))。电荷转移过程使我们能够实现各种离子的交感冷却。由于镁离子的能级结构简单，一束激光就能很容易地冷却镁离子。镁离子的电荷和“冷温度”通过碰撞传递给客体离子。我们观察到的共感冷却钡离子的温度为500K，远低于氦缓冲气冷却离子的温度（4000K）。我们计算了共感冷却所达到的极限温度作为离子温度和离子质量的函数。我们的理论模型在一对镁离子和钡离子中得到了实验证实。该理论预测，当主离子温度较低时，较重的客体离子冷却效率较高，而在较高温度区域，客体离子温度随质量的增加而迅速升高。本文还研究了共感冷却离子在射频阱中的谐振振荡模式。观察到两种类型的集体振荡。振荡频率可以用理论模型计算，与观测结果吻合较好。不相关的离子可以通过对离子的适当频率施加射频电压谐振而从阱中移除。

The charge transfer process between a laser cooled magnesium ion and a thermal barium atom is successfully observed in a radio frequency ion trap in extremely low energy regime. The merit of ion trap experiment is that the generated ion is also trapped and very high sensitivity is achieved. The production of barium ion is confirmed by observing the laser-induced fluorescence from the ion.The cross section is estimated to be 10^<-4> nm^2. This well agrees with the value calculated from a theory in the reference (D. Rapp and W.E.Francis, J. Chem. Phys. 37, 2631(1962)).The charge transfer process allows us to achieve sympathetic cooling of various ions. The magnesium ion is easily cooled by a single laser, because its energy level structure is simple. The charge and "cold temperature" of magnesium ion are transferred to guest ions through collisions. We observed the temperature of sympathetically cooled barium ion of 500K, which is much smaller than that of the ion cooled by Helium buffer gas (4000K). We have calculated the limiting temperatures achieved by the sympathetic cooling as functions of ion temperatures and ion masses. The experimental confirmation of our theoretical model is achieved in a pair of magnesium and barium ions. The theory predicts that when the temperature of host ion is low the heavier guest ions are cooled more efficiently, while the guest ion temperature increases rapidly with increasing mass in higher temperature region. The resonant oscillation modes of sympathetically cooled ions in a radio frequency trap are also investigated through charge transfer process in the trap. Tow types of collective oscillation are observed. The frequency of oscillation can be calculated by a theoretical model, which agrees well with the observation. Irrelevant ions can be removed from the trap by applying an rf-voltage resonant to the proper frequency of the ions.