图 1  超冷离子源的发展路线和重要研究进展

Fig. 1.  Roadmap and advances of ultracold ion source.

图 2  原子的一维冷却示意图　(a)速度为$ {\mathrm{\nu }} $的原子与动量为$ {\mathrm{\hslash }}\kappa $在单方向上的光子相互作用; (b)原子吸收定向光子后, 速度减小了$ \hslash \kappa /m $; (c)激发态原子经自发辐射过程随机释放光子回到基态; (d)二能级系统中原子对负失谐光子的吸收($ \hslash \omega $)和发射过程($ \hslash {\omega }_{0} $)

Fig. 2.  The schematic of one-dimensional cooling atoms: (a) An incoming atom with velocity $ {\mathrm{\nu }} $ interaction with laser with the specific momentum $ {\mathrm{\hslash }}\kappa $ in a single direction; (b) the photon is absorbed and the velocity of the atom has been reduced $ \hslash \kappa /m $ induced by the net momentum transfer; (c) after spontaneous emission, the excited state atom emits a photon in all directions; (d) in a two-level system, the absorption of a red-detuned photon by an atom and the subsequent emission process.

图 3  电离过程的3种模式示意图^[17]　(a) 轴向电离模式; (b) 横向电离模式; (c) 交叉双光子模式

Fig. 3.  The sketch of ionization modes in a MOTIS^[17]: (a) Axial mode; (b) transverse mode; (c) two-photon mode

图 4  能散和束流能量除电荷量后的关系, 插图为5种不同束流电荷量下能散与束流能量的关系^[35]

Fig. 4.  The five measured energy spread and beam energy curves from inset scaled by the bunch charge to a single curve. The inset shows the measured energy spread as a function of the beam energy for five different bunch charges^[35]

图 5  含时电场对超冷离子束相空间的操控　(a)纵向相对能散σ_U/U与脉冲电场宽度U之间的关系; (b)双极性电场(V_p = 1000 V)条件下, 离子束在x方向上的横向尺寸σ_x 与V_n 的函数关系^[36]

Fig. 5.  Phase-space manipulation of ultracold ion bunches with time-dependent fields: (a) The longitudinal relative energy spread σ_U/U versus U is plotted; (b) demonstration of focusing by bipolar voltage pulses with V_p = 1000 V, the transverse size in the x direction σ_x of the bunch on the detector is measured as a function of V_n^[36].

图 6  离子束斑与束流能量倒数的关系, 其斜率与有效源温度T成正比, 图中实心点为实验测量结果, 红色实线代表线性拟合^[38]

Fig. 6.  Final spot radius squared $ {\sigma }_{x{\mathrm{f}}}^{2} $ vs. the reciprocal of the bunch energy 1/U, the thick line is a linear fit, the slope of which is proportional to the effective source temperature T^[38].

图 7  四种离子束分布及其空间电荷驱动的扩散^[39]　(a) 径向平均激发光轮廓(实线)与相对激发概率(虚线)的关系; (b) 径向扩散因子与离子数的关系

Fig. 7.  Four ion bunch distributions and their expansion properties^[39]: (a) Measured radially averaged excitation laser profiles (solid lines) and desired profiles (dashed lines), plotted as the relative excitation probability; (b) radial expansion factors against ion number for each shape individually.

图 8  分子动力学模拟里德伯阻塞机制抑制无序诱导加热^[40] 　(a)不同阻塞半径条件下, 离子平衡时的发射度和温度随扩散时间的关系; (b)不同扩散时间下, 不同阻塞半径对于阻塞与无序发射度比率的影响

Fig. 8.  Rydberg blockade mechanism suppressing disorder-induced heating with molecular dynamics simulation^[40]: (a) The relationship between the emittance and temperature of ions at equilibrium under different blocking radii, as a function of diffusion time; (b) suppression of disorder-induced heating, expressed as the ratio of blockaded to disordered emittance for different blockade parameters at different expansion times.

图 9  冷离子源中电场分布测量^[41]　(a)实验装置示意图; (b)⁸⁵Rb能级示意图及光电离和激发所需的激光波长; (c)低离子计数率和(d)高离子计数率条件下, 实验测量的57F_5/2的Stark 图; (e), (f)对应的模拟Stark图

Fig. 9.  Measurement of electric field in a cold ion source^[41]: (a) Sketch of the experimental setup; (b) diagram of the utilized ⁸⁵Rb energy levels and configuration of laser beams for photoionization and excitation; (c), (d) experimental Stark maps of 57F_5/2 and the neighboring hydrogenic states at the different γ values; (e), (f) the corresponding simulated Stark maps with empirically determined ion rates.

图 10  Cr-MOTIS装置示意图^[43]

Fig. 10.  The schematic of Cr-MOTIS^[43].

图 11  Li-MOTIS-FIB装置示意图^[45]

Fig. 11.  The sketch of Lithium FIB system ^[45].

图 12  (a) Li-MOTIS装置示意图; (b)不同紫外激发功率(P_exc)下离子源亮度(B_p)与束流流强(P_exc)的关系^[47]

Fig. 12.  (a) Schematic of Li-MOTIS; (b) peak normalized brightness (B_p) as a function of total current (I_tot) for a range of UV excitation powers (P_exc)^[47].

图 13  场电离里德伯态原子方案的CABIS装置结构示意图^[23], 利用2D-MOT技术对高通量原子束进行横向冷却和压缩, 离子或电子(取决于电极的极性)由场电离冷里德伯态原子产生, 之后束流在FIB系统中被加速和聚焦

Fig. 13.  Sketch of the ultracold electron-ion source producing from CABIS^[23], an intense effusive atomic beam is transversely cooled and compressed using laser-cooling techniques, electrons or ions (depending on electrode polarities) are produced by laser excitation to Rydberg states that are then field ionized, the beam is finally focused and accelerated in a FIB column.

图 14  拍摄的碳衬底上锡球的图像比较　(a)束流能量5 keV, 束流电流7 pA的Cs⁺-FIB; (b)束流能量5 keV, 束流电流20 pA的商业化产品Ga-LMIS FIB^[50]

Fig. 14.  Comparison between images acquired on a tin on carbon test sample: (a) Our system at 5 keV ion beam energy and 7 pA current; (b) a commercial Ga-LMIS FIB at 5 keV ion beam energy and current 20 pA^[50].

图 15  腔增强电离方案的CABIS装置结构示意图(未按比例绘制)^[51]

Fig. 15.  Schematic diagram of the experimental setup (not drawn to scale) of CABIS for the cavity enhanced photoionization^[51].

图 16  Rb-CABIS-FIB装置示意图(左), 不同剂量Rb⁺和Ga⁺刻蚀材料的SEM图像(右图)　(a) 8.5 keV的Rb⁺刻蚀后GaAs靶俯视图; (b) 多晶Au靶俯视图(0°); (c) Au靶侧视图(52°); (d)多晶Cu靶侧视图(52°); (e) 30 keV的Ga⁺刻蚀后Cu靶侧视图(52°)^[53], 标尺为1 μm

Fig. 16.  Schematic of corresponding Rb-CABIS-FIB (left), SEM images of Rb⁺ and Ga⁺ milling patterns on standard samples (right): (a) Top view (0°) of milling patterns on GaAs at 8.5 keV; (b) top view (0°) of milling patterns on polycrystalline Au; (c) tilt view (52°) of (b); (d) tilt view (52°) of milling patterns on polycrystalline Cu; (e) tilt view (52°) of 30 keV Ga⁺ milling patterns on polycrystalline Cu, ion dose is marked below each pattern^[53], scale bar is 1 μm.

图 17  (a)慢原子束CABIS装置结构示意图, 显示了离子束产生的4个阶段, 即带推杆束磁光压缩器的二维磁光阱、光学糖蜜和电离; (b)标准锡球二次电子图像, 获取自CABIS的聚焦10 keV, 1 pA Cs+离子束^[60]

Fig. 17.  (a) Schematic of the slow cold atomic beam ion source, showing the four stages of ion beam production: 2D magneto-optical trap with pusher beam magneto-optical compressor, optical molasses, and ionization; (b) secondary electron image of a standard tin ball resolution target acquired using a focused 10 keV, 1 pA Cs⁺ ion beam from the CABIS^[60].

图 18  (a) 单离子显微镜示意图; (b) 波导腔结构的SEM图像, 孔直径约为150 nm; (c)单离子源成像结果, 分辨率为每像素(25 nm×25 nm), 图中的全部信息基于4141个提取的离子中的2659个; (d)泊松分布的离子源成像结果^[66]

Fig. 18.  (a) Sketch of the single ion microscope; (b) SEM image of the waveguide-cavity structure, holes have a diameter of about 150 nm; (c) scan of the cavity structure using one ion at each lateral position, with a resolution of (25 nm× 25 nm) per pixel, the entire information in the picture is based on 2659 transmission events out of 4141 extracted ions; (d) imaging a source with emulated Poissonian behavior^[66].

图 19  (a) 单离子注入装置的示意图; (b)离子荧光的成像; (c) Ca⁺和Pr⁺离子束斑测量的直方图^[67]; (d)植入区域的共聚焦显微镜图像^[68]

Fig. 19.  (a) Sketch of the single-ion implantation setup; (b) fluorescence of ions imaged; (c) histograms of the profiling edge measurement for Ca⁺ and Pr⁺ ions^[67]; (d) confocal images of the implanted regions ^[68].

图 20  电子-离子符合装置示意图^[69]

Fig. 20.  Schematic of the electron-ion coincidence apparatus ^[69]

图 21  (a)实验装置及流程示意图; (b)选定区域离子轨迹二维校正; (c) 在FPGA中实现的虚拟掩模的应用^[72]

Fig. 21.  (a) Sketch of experiment set and procedure; (b) 2D correction on a selected zone for the ion trajectory; (c) application of a virtual mask implemented in the FPGA^[72].