GOALI: Resolving Outstanding Questions in Spin-Exchange Optical Pumping of 129Xe

磁共振成像的气体内的肺部或其他类似的空间，其中气体可以允许利用作为活性介质惰性气体，其具有对齐的磁核指向相同的方向，一个过程被称为惰性气体MRI。 只有通过自旋交换光泵浦（SEOP）来提高灵敏度，以制备用于成像过程的自旋极化惰性气体样品（氦-3或氙-129），才有可能有效地使用今天的过程。这项研究的重点是SEOP过程本身，其中角动量首先从光转移到吸收光的碱金属原子，然后通过碰撞将动量转移到惰性气体原子。碰撞使磁核对齐（或重叠），使它们的北磁极和南磁极相互对齐，从而使它们对MRI研究有用。该项目将解决一些悬而未决的问题，有关SEOP的效率如何取决于激光功率，激光带宽，碱金属原子的选择，以及气体混合物中缓冲气体的压力。氙-129（129 Xe）的SEOP特别令人感兴趣，因为它不太容易理解，并且因为它可能取代氦-3作为惰性气体MRI的选择原子。GOALI项目的工业合作伙伴Polarean公司，处于129 Xe-MRI技术发展的最前沿。该项目将使大学研究人员能够与Polarean公司合作。研究与129欧姆SEOP相关的物理问题，并利用所得知识改进商业偏振装置。三个主要的研究目标是：（1）推动铷-129 SEOP向超快速率发展：目标是在研究较少的低缓冲气体密度区域（~ 0.1 amagat）中展示和实现自旋交换效率的定量增益。超窄的OptiGrate激光器允许显著的光沉积，即使是在这种情况下窄得多的铷D1吸收线。(We请注意，Optigrate是该项目的第二个工业合作者。）(2)用于SEOP的铷和铯的直接比较：目标是使用双头高功率Rb/Cs二极管激光器的共同平台对Rb-129 Xe和Cs-129 Xe SEOP参数进行定量测量，以确定Cs是否有利以及在多大程度上有利。(3)碱金属团簇在限制SEOP效率中的作用：目标是获得SEOP偏振器中这些潜在有害纳米团簇的直接证据，并将其影响纳入129 Ω SEOP的“标准模型”。满足这些目标中的每一个都对129 μ S SEOP的效率有直接影响，阐明了一些有趣的（迄今为止难以捉摸的）物理学，同时也导致了HP 129 μ S在肺部MRI等应用中的生产改进。

Magnetic resonance imaging of gas inside the lungs or other similar spaces where gases can be admitted utilizes as the active medium noble gases that have had their magnetic nuclei aligned to point in the same direction, a process known as noble-gas MRI. Effective use of the process today is only possible if the sensitivity is enhanced by spin-exchange optical pumping (SEOP) for preparing the spin-polarized noble gas samples (helium-3 or xenon-129) to be used in the imaging procedure. This research focuses on the SEOP process itself, in which angular momentum is transferred first from light to alkali-metal atoms that absorb the light and then transfer the momentum to the noble-gas atoms through collisions. The collisions align (or polarize) the magnetic nuclei, bringing their north and south magnetic poles in mutual alignment, thereby rendering them useful for MRI studies. This project will address some open questions relating to how the efficiency of SEOP depends on the laser power, the laser bandwidth, the choice of alkali-metal atoms, and the pressure of the buffer gas in the gas mixtures. SEOP of xenon-129 (129Xe) is of particular interest because it is less well understood, and because it may supersede helium-3 as the atom of choice for noble-gas MRI. The industrial partner for this GOALI project, Polarean, Inc., is at the forefront of 129Xe-MRI technological development. This project will enable university researchers to collaborate with Polarean, Inc. to study physics issues related to SEOP of 129Xe, and to use the resulting knowledge to improve a commercial polarization device. The three main research aims are: (1) Pushing Rubidium-129Xe SEOP toward ultra-fast rates: The goal is to demonstrate and implement quantitative gains in the spin-exchange efficiency in the less-studied low-buffer-gas-density regime (~ 0.1 amagat). The ultra-narrow OptiGrate laser allows significant light deposition even for the much narrower rubidium D1 absorption line in this regime. (We note that Optigrate is a second industrial collaborator in this project.) (2) Direct comparison of rubidium to cesium for use in SEOP: The goal is to make quantitative measurements of Rb-129Xe and Cs-129Xe SEOP parameters using the common platform of the dual-head high-power Rb/Cs diode laser, in order to determine whether and to what degree Cs is advantageous. (3) The role of alkali-metal clusters in limiting SEOP efficiency: The goal is to obtain direct evidence for these potentially deleterious nanoclusters in a SEOP polarizer and incorporate their effects into the "standard model" for 129Xe SEOP. Meeting each of these goals has a direct impact on the efficiency of 129Xe SEOP, elucidating some interesting (and heretofore elusive) physics while also leading to improved production of HP 129Xe for applications such as lung MRI.