Statistical properties of laser-cooled Ca ions in a quadrupole toroidal rf trap

在我们的实验中，离子被限制在环形射频阱中，并通过激光冷却实现库仑耦合参数>1。为了冷却Ca+离子，使用二极管激光器构建了397 nm辐射和866 nm辐射，所述397 nm辐射是通过使用放置在外腔中的LBO晶体对794 nm辐射进行倍频而获得的。我们已经通过来自Littrow配置中的全息光栅的反馈为两个二极管激光器构造了光栅激光稳定系统。结果，实现了二极管激光器在频率、强度和指向方面的稳定。采用He缓冲气体冷却的方法控制Ca ~+离子温度;利用激光诱导荧光（LIF）方法测量了Ca ~+离子的约束时间、速度分布函数和密度分布。2002年，我们在冷却激光器的基础上，构建了第二台397 nm激光器作为探测激光器，用于测量激光冷却Ca ~+离子的统计特性，如速度分布函数和密度剖面。采用比例积分（PI）反馈方法，分别用1f和3f电反馈同时控制光栅稳频激光器的光反馈相位和频率，实现了近5GHz的频率扫描。在相邻电极之间的距离上，一个是2 mm，另一个是4 mm（在两个阱中，主半径是40 mm）。而2 mm阱在没有缓冲气体冷却的情况下没有显示出LIF信号，4 mm阱甚至在基准压力下显示出捕获的Ca+离子的证据。激光冷却实验正在进行中，使用4毫米的陷阱。

In our experiments, ions are confined in a toroidal rf trap and Coulomb coupling parameter >1 is achieved by laser cooling. In order to cool Ca+ ions, the 397 nm radiation, obtained by frequency doubling of the 794 nm radiation using a LBO crystal placed in the external cavity, and the 866 nm radiation are constructed using diode lasers.In 2001, to achieve stable radiations of 397 nm and 866 nm from diode lasers, we have constructed grating-laser-stabilization systems by means of feedback from holographic gratings in the Littrow configuration for both diode lasers. As a result, stabilization of diode lasers in frequency, intensity, and pointing has been achieved. We have controlled the Ca+ ion temperature by means of He buffer-gas-cooling ; and measured confinement time, velocity distribution function, and density profile of Ca+ ions using laser-induced fluorescence (LIF) method.In 2002, we have constructed the second 397 nm laser as a probe laser in addition to the cooling laser, in order to measure the statistical properties of laser-cooled Ca+ ions, such as velocity distribution function and density profile using LIF method. The optical feedback phase and the frequency of the grating-stabilized laser are simultaneously controlled by 1f and 3f electric feedback, respectively, using a proportional and integral (PI) feedback method, and the frequency scan of nearly 5 GHz is achieved.We have conducted LIF measurements of Ca+ ions using two toroidal rf traps ; one is 2 mm and the other is 4 mm in the distance between the neighboring electrodes (the major radius is 40 mm in both traps). Whereas the 2 mm trap has shown no LIF signals without the buffer-gas cooling, the 4 mm trap has shown the evidence for trapped Ca+ ions even at the base pressure. Laser-cooling experiments are in progress using the 4 mm trap.