Laser cooling of one-component plasma and drive of troidal flow

本实验的目的是：(1)将Ca^+离子限制在环形射频阱中（主半径为40 mm），通过激光冷却获得库仑耦合参数Γ>1;(2)控制射频阱在三线方向的电位，驱动激光冷却的Ca^+离子在三线方向上运动。为了冷却Ca^+离子，用光栅-激光稳定系统产生了397 nm和866 nm的辐射，其中采用了Littrow构型全息光栅的反馈稳定。397纳米的激光是通过将二极管激光器的794纳米的光加倍产生的。为此，采用了包含非线性晶体（LBO）的外部增强腔。397 nm和866 nm激光束共线重叠并切向聚焦在被捕获的离子上。采用比例反馈和积分PI （PI）反馈方法，分别采用1f和3f电反馈控制光栅稳定397 nm激光器的光反馈相位和频率。实现了近5 GHz的频率扫描。采用397 nm的激光诱导荧光（LIF）检测Ca^+离子。我们通过将单侧接地（OG）射频阱改为中心接地（CG）射频阱来改善Ca^+离子的约束。当使用OG射频阱时，可能由于射频阱充电产生的残余电场，Ca^+离子被限制在电子枪的射频电压（V_< rf >）和电流（I_b）的狭窄区域内，Ca^+离子被电离。当使用CG射频阱时，消除了残余电场，在V_< rf >和I_b的宽区域内实现了Ca^+离子的约束。结果，我们观察到非线性共振效应引起的约束离子数和约束时间的减少。然而，由于激光冷却所必需的高真空约束时间较短，并且在397 nm激光器的波长扫描过程中离子丢失，因此无法实现Ca^+离子的激光冷却。射频阱需要进一步改进。少

The purpose of this experiment is (1)to confine Ca^+ ions in a toroidal rf trap (the major radius is 40 mm) and achieve Coulomb coupling parameter Γ>1 by laser cooling and (2)to control a potential of the rf trap in a troidal direction to drive laser-cooled Ca^+ ions in the troidal direction.In order to cool Ca^+ ions, 397 nm and 866 nm radiation were produced by diode lasers with a grating-laser-stabilization systems, in which feedback stabilization from holographic grating in the Littrow configuration was used. The 397 nm laser light was produced by doubling the 794 nm light of a diode laser. For this purpose, an external enhancement cavity containing the nonlinear crystal (LBO) was used. The 397 nm and 866 nm laser beams were collinearly overlapped and focused tangentially on the trapped ions. The optical feedback phase and the frequency of the grating-stabilized 397 nm laser were simultaneously controlled by 1f and 3f electric feedbacks, respectively, using a proportional and integ … More ral(PI) feedback method. The frequency scan of nearly 5 GHz was achieved. The laser-induced fluorescence (LIF) of the 397 nm radiation was used for the detection of Ca^+ ions.We improved confinement of Ca^+ ions by changing an one-side-grounded(OG) rf trap to a center-grounded(CG) rf trap. When the OG rf trap was used, possibly due to a residual electric field caused by the charging of the rf trap, Ca^+ ions were confined in narrow regions of rf voltage(V_<RF>) and current(I_b) of electron-gun, by which Ca^+ ions are ionized. When the CG rf trap was used, the residual electric field was removed and confinement of Ca^+ ions were achieved in wide regions of V_<RF> and I_b. As a result, we have observed the reduction of both the number of confined ions and confinement time caused by the nonlinear-resonance effect. However, laser cooling of Ca^+ ions was not achieved since the confinement time at high vacuum, which is necessary in laser cooling, was short and ions were lost during the wavelength-scan of the 397 nm laser. Further improvement of rf trap is required. Less