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，并通过激光冷却获得库仑耦合参数>1。为了冷却Ca+离子，利用放置在外腔内的LBO晶体将794 nm的辐射频率加倍得到397 nm的辐射，并利用二极管激光器构建866 nm的辐射。2001年，为了从二极管激光器获得397 nm和866 nm的稳定辐射，我们在Littrow配置中利用全息光栅的反馈构建了光栅激光稳定系统。因此，稳定的二极管激光器的频率，强度和指向已经实现。我们用He缓冲气冷的方法控制了Ca+离子的温度；并利用激光诱导荧光（LIF）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，构建了第二个397nm的探测激光器，用LIF方法测量了激光冷却后Ca+离子的速度分布函数和密度分布等统计特性。采用比例和积分（PI）反馈方法，分别通过1f和3f电反馈控制光栅稳定激光器的光反馈相位和频率，实现了近5 GHz的频率扫描。我们使用两个环形射频阱对Ca+离子进行了LIF测量；一个是2毫米，另一个是4毫米，在邻近的电极之间的距离（在两个陷阱的主要半径是40毫米）。在没有缓冲气体冷却的情况下，2毫米的陷阱没有显示出LIF信号，而4毫米的陷阱即使在基压下也显示出捕获Ca+离子的证据。使用4毫米阱的激光冷却实验正在进行中。

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.