Department of Applied Physics, Eindhoven University of Technology, P.O. Box 513, Eindhoven, 5600 MB, The Netherlands.
Department of Applied Physics, Eindhoven University of Technology, P.O. Box 513, Eindhoven, 5600 MB, The Netherlands.
Ultramicroscopy. 2018 Jul;190:12-20. doi: 10.1016/j.ultramic.2018.03.014. Epub 2018 Apr 5.
The energy distribution of a high brightness rubidium ion beam, which is intended to be used as the source for a focused ion beam instrument, is measured with a retarding field analyzer. The ions are created from a laser-cooled and compressed atomic beam by two-step photoionization in which the ionization laser power is enhanced in a build-up cavity. Particle tracing simulations are performed to ensure the analyzer is able to resolve the distribution. The lowest achieved full width 50% energy spread is (0.205 ± 0.006) eV, which is measured at a beam current of 9 pA. The energy spread originates from the variation in the ionization position of the ions which are created inside an extraction electric field. This extraction field is essential to limit disorder-induced heating which can decrease the ion beam brightness. The ionization position distribution is limited by a tightly focused excitation laser beam. Energy distributions are measured for various ionization and excitation laser intensities and compared with calculations based on numerical solutions of the optical Bloch equations including ionization. A good agreement is found between measurements and calculations.
采用减速场分析器测量了拟用作聚焦离子束仪器源的高亮度铷离子束的能谱分布。离子由激光冷却和压缩的原子束通过两步光电离产生，其中在建立腔中增强了电离激光功率。进行粒子跟踪模拟以确保分析器能够解析分布。在 9 pA 的束流下，实现的最低全宽 50%能量展宽为 (0.205±0.006) eV。能量展宽源于在引出电场中产生的离子的电离位置的变化，该引出电场对于限制由无序引起的加热至关重要，因为这种加热会降低离子束亮度。离子化位置分布受紧密聚焦的激发激光束限制。测量了各种电离和激发激光强度下的能量分布，并与基于包括电离的光学布洛赫方程数值解的计算进行了比较。在测量和计算之间发现了很好的一致性。
