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颖的“交钥匙”极化电子束源。从探测核子和原子核的自旋结构到研究磁畴结构和原子碰撞的自旋依赖性，极化电子的使用在物理学中是广泛的。最先进的极化电子源是基于砷化镓光电阴极技术。虽然这种来源比其他可用的方法有显著的优点，但操作起来非常困难。在大学环境中，研究生对这些资源的可靠操作的学习曲线通常以月或年为单位，而不是以周为单位。在CEBAF或MAMI等加速器设施中，由技术人员和博士组成的专职人员维护和操作这些源。所开发的极化电子源是基于光抽运铷自旋滤光片这一新技术。在该方案中，非极化电子在电场作用下通过光抽运Rb靶和缓冲气体扩散。当电子与自旋极化的Rb碰撞时，它们通过交换碰撞变得极化。然后将它们提取出来并形成光束。一个原理验证实验已经证明了这种技术。这样的来源有望使许多当前的实验更容易，它也将扩大他们产生的数据的范围和质量。更重要的是，它可能会引导目前在极化电子技术方面没有专业知识的小组考虑新型实验。例如，自旋极化低能显微镜（SPLEEM）是一项强大的磁表面研究技术，由于其使用的GaAs源的操作复杂性，目前仅在世界各地的少数实验室中使用。自旋过滤器将使这种技术更容易为一般凝聚态物质社区所接受。研究Rb自旋滤波器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。该光源的关键要素是光泵浦，这是其他领域的使能技术，如核物理和医学。参与这个项目的教师在将本科生融入他们的研究项目方面非常有效。他们做出了特别大的努力，在学术“管道”的早期雇佣和指导女性和未被充分代表的少数族裔。这项仪器开发工作的成果将通过经审定的科学出版物广泛传播，并将评价其商业化的潜力。

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.