MRI: Development of a Rubidium Spin Filter as a Source of Polarized Electrons

内布拉斯加州大学林肯分校的一个物理学家团队将开发一种新型的“交钥匙”偏振电子束源。极化电子在物理学中的应用非常广泛，从探测核子和原子核的自旋结构到研究磁区结构和原子碰撞的自旋相关性。最先进的极化电子源是基于砷化镓光电阴极技术的。虽然这种方法与其他可用的方法相比具有显著的优势，但操作起来非常困难。在大学环境中，研究生可靠操作这些信号源的学习曲线通常是以月或年来衡量的，而不是以周来衡量的。在CEBAF或MAMI等加速器设施中，由技术人员和博士组成的专职员工负责维护和操作这些源。将开发的极化电子源基于新技术：光泵路自旋滤光器。在这个方案中，未极化的电子在电场的作用下通过光泵浦的Rb靶和缓冲气体扩散。当电子与自旋极化的RB碰撞时，它们通过交换碰撞而变得极化。然后它们被提取并形成一束光束。一项原理验证实验已经演示了这项技术。这样的来源预计将使目前的许多实验变得更容易，它还将扩大它们产生的数据的范围和质量。更重要的是，它可能会让目前在极化电子技术方面没有专业知识的团队考虑进行新类型的实验。例如，自旋极化低能显微镜(SPLEEM)是一种研究磁性表面的强大技术，由于其所使用的砷化镓光源的操作复杂性，目前仅在世界各地的几个实验室中使用。自旋过滤器将使这种技术更容易为普通凝聚态社区所接受。致力于RB自旋过滤器开发的学生和博士后将接受最先进的光学仪器和技术方面的培训。这种光源的关键要素是光学泵浦，这是一项使其他领域能够实现的技术，如核物理和医学。参与这个项目的教职员工在将本科生融入他们的研究项目方面一直非常有效。他们做出了特别大的努力来雇佣和指导女性和在学术“管道”早期代表不足的少数族裔。这项仪器开发工作的结果将通过参考的科学出版物广泛传播，并将对商业化的潜力进行评估。

A team of University of Nebraska-Lincoln physicists will develop a novel, "turn-key" polarized electron beam source. The use of polarized electrons is widespread in physics, from probing the spin-structure of nucleons and nuclei to studies of magnetic domain structure and the spin-dependence of atomic collisions. State-of-the-art polarized electron sources are based on GaAs photocathode technology. While this source has significant advantages over other available methods, it is very difficult to operate. In university settings, the learning curve for reliable operation by a graduate student of these sources is routinely measured in months or years, not weeks. At accelerator facilities such as CEBAF or MAMI, dedicated staffs of technicians and Ph.D.s maintain and operate these sources. The polarized electron source to be developed is based on new technology: the optically-pumped rubidium spin filter. In this scheme, unpolarized electrons diffuse under the action of an electric field through a target of optically-pumped Rb and a buffer gas. As the electrons collide with the spin-polarized Rb, they become polarized via exchange collisions. They are then extracted and formed into a beam. A proof-of-principle experiment has already demonstrated this technique. Such a source is expected make many current experiments easier, and it would also extend the range and quality of the data they produce. More importantly, it may lead groups with no current expertise in polarized electron technology to consider new types of experiments. As an example, spin-polarized low-energy microscopy (SPLEEM), a powerful technology for the study of magnetic surfaces, is currently used in only a few labs around the world due to the operational complexity of the GaAs sources it employs. A spin filter would make such technology much more accessible to the general condensed matter community. Students and postdocs working on the development of the Rb spin filter will receive training in state-of-the-art optical instrumentation and technology. The key element of this source is optical pumping, which is an enabling technology for other fields, such as nuclear physics and medicine. The faculty involved with this project have been very effective at integrating undergraduate students into their research programs. They have made a particularly strong effort to hire and mentor women and underrepresented minorities early in the academic "pipeline." The results of this instrument development effort will be broadly disseminated through refereed scientific publications, and the potential for commercialization will be evaluated.