用于离子-分子交叉分子束散射研究的三维离子速度成像装置

本文设计、模拟并搭建了一套由22片圆形金属极板组成的离子透镜系统. 离子透镜的引出极板的开孔处贴有金属栅网，用于屏蔽除推斥极和引出极外的所有其他极板的直流高压对离子-分子交叉区域的影响. Simion模拟表明，在合适的电压配置下，离子透镜可以同时实现速度聚焦和时间聚焦. 这使离子透镜系统能够在三个维度上实现较大的离子体积的速度聚焦，这也是用交叉分子束方法研究离子-分子散射动力学的基本要求. 本文建立了具有单帧多粒子测量和多质量测量能力的三维离子速度测量系统，该系统由微通道板(MCP)，P47荧光屏，CMOS相机、光电倍增管(PMT)、高速数字化仪组成. 通过CMOS相机测量离子在荧光屏上的位置，得出垂直于飞行轴的两个速度分量；通过PMT测量离子的飞行时间，得出沿着飞行轴的速度分量. 自主编写了Labview程序，可以实时采集和分析CMOS相机与PMT得到的数据，构建离子的三维速度分布. 单帧多粒子测量是根据同一帧中来自CMOS相机和PMT的多个离子的强度不同，分别对其进行排序，并一一对应起来实现的. 本文用304 nm波长处碘甲烷的光解信号对该三维离子速度成像系统进行了测试和速度校订.

A Three-Dimensional Velocity-Map Imaging Setup Designed for Crossed Ion-Molecule Scattering Studies

In this study, we report the design and simulation of an electrostaticion lens system consisting of 22 round metal plates. The opening of the extractor plate is covered with metal mesh, which is for shielding the interaction region of the lens system from the high DC voltages applied to all other plates than the repeller and extractor plates. The Simion simulation shows that both velocity-mapping and time focusing can be achieved simultaneously when appropriate voltages are applied to each of the plates. This makes the ion lens system be able to focus large ionic volumes in all three dimensions, which is an essential requirement for crossed ion-molecule scattering studies. A three-dimensional ion velocity measurement system with multi-hit and potential multi-mass capability is built, which consists of a microchannel plate (MCP), a P47 phosphor screen, a CMOS camera, a fast photomultiplier tube (PMT), and a high-speed digitizer. The two velocity components perpendicular to the flight axis are measured by the CMOS camera, and the time-of-flight, from which the velocity component along the flight axis can be deduced, is measured by the PMT. A Labview program is written to combine the two measurements for building the full three-dimensional ion velocity in real time on a frame-by-frame basis. The multi-hit capability comes from the fact that multiple ions from the camera and PMT in the same frame can be correlated with each other based on their various intensities. We demonstrate this by using the photodissociation of CH₃I at 304 nm.