Laser-Assisted Inelastic Electron-Atom Scattering

激光辅助非弹性电子原子散射

• 批准号: 2010102
• 负责人: Nicholas L.S. Martin
• 金额: $ 26.41万
• 依托单位: University of Kentucky Research Foundation
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2020
• 资助国家: 美国
• 起止时间: 2020-08-15 至 2024-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2010102&HistoricalAwards=false
• 关键词: Laser; Assisted; Inelastic; Electron; Atom

Free-free scattering is a fundamental process that is important for the understanding of various astrophysical phenomena. The process is named for the fact that when an electron scatters from an atom in the presence of a photon field, the electron can absorb or emit one or more photons (particles of light), but the electron is free both before and after the scattering collision. Almost all experiments to date indicate that the photon interacts only with the free electron and has no effect on the target atom. However, it has been shown that a so-called "dressed atom" effect (the interaction of the photon field with the target atom) can greatly enhance the probability of the free electron absorbing or emitting a photon for very small electron scattering angles. This project investigates free-free scattering in the laboratory by using a laser to produce a well-defined photon beam, an electron gun (similar to those that used to be found in old TV sets) to produce a well-defined electron beam, with the two beams arranged to intersect each other and a beam of atoms. An important part of the project is to look for "dressed atom" effects in helium, for the special case where the scattered electron also changes the energy state of the helium atom. This work will have a broad impact on the community by providing educational opportunities for students at the high school, undergraduate, and graduate levels in the EPSCoR state of Kentucky and in collaboration with the exclusively undergraduate institution Illinois Wesleyan University.This project concerns fundamental research on laser-assisted electron scattering. The work will be carried out on two apparatuses. The first, which is already in use for such experiments, will be used to measure the effects of the "dressing" of the lowest excited states of He atoms by 1.17 eV laser radiation during inelastic electron scattering. The electron gun of this apparatus will be fitted with a monochrometer in order to resolve the closely spaced He 1s2s and 1s2p singlet levels; only the former is expected to show dressing effects and it is important to eliminate the effect of the large scattering cross section of the latter. The apparatus will also be interfaced with an in-house developed multipass laser system to increase the free-free count rate; to date such systems have only been used in national labs, never in "tabletop" experiments. The multipass system uses a Pockels cell to rotate the linearly polarized laser beam 90 degrees after injection, combined with a beam splitting cube that then traps the laser beam into a repetitive path (that includes the now-deactivated Pockels cell). The second apparatus has recently been fitted with such a multipass laser system. This apparatus will be used to investigate laser-assisted electron-impact autoionization of helium. The expected signatures of laser assisted autoionization are sidebands in the ejected-electron spectrum, one photon energy away from the autoionizing resonance positions. Such sidebands have been seen by other workers in Auger decay, but have never been observed for the autoionization process.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

自由散射是一个基本过程，对于理解各种天体物理现象非常重要。该过程因以下事实而得名：当电子在存在光子场的情况下从原子中散射时，电子可以吸收或发射一个或多个光子（光粒子），但电子在散射之前和之后都是自由的碰撞。迄今为止几乎所有的实验都表明光子只与自由电子相互作用，对目标原子没有影响。然而，已经表明，所谓的“修饰原子”效应（光子场与目标原子的相互作用）可以极大地提高自由电子在非常小的电子散射角下吸收或发射光子的概率。该项目在实验室中研究自由散射，方法是使用激光产生明确的光子束，使用电子枪（类似于旧电视机中使用的电子枪）产生明确的电子束，两根相互交叉的光束和一束原子。 该项目的一个重要部分是寻找氦中的“修饰原子”效应，针对散射电子也会改变氦原子能量状态的特殊情况。这项工作将与伊利诺伊州卫斯理大学合作，为肯塔基州 EPSCoR 州的高中、本科生和研究生水平的学生提供教育机会，从而对社区产生广泛的影响。该项目涉及以下方面的基础研究：激光辅助电子散射。这项工作将在两台设备上进行。第一个已用于此类实验，将用于测量非弹性电子散射过程中 1.17 eV 激光辐射对 He 原子最低激发态的“修饰”效果。该装置的电子枪将配备单色仪，以解析紧密间隔的 He 1s2s 和 1s2p 单线态能级；只有前者有望表现出修整效果，重要的是消除后者大散射截面的影响。该设备还将与内部开发的多通道激光系统连接，以提高自由计数率；迄今为止，此类系统仅在国家实验室中使用，从未用于“桌面”实验。多通道系统使用普克尔斯盒将线偏振激光束在注入后旋转 90 度，并结合分束立方体，然后将激光束捕获到重复路径（包括现已停用的普克尔斯盒）。第二台设备最近配备了这种多通道激光系统。该装置将用于研究氦的激光辅助电子轰击自电离。激光辅助自电离的预期特征是喷射电子光谱中的边带，即远离自电离共振位置的一个光子能量。其他工作人员在俄歇衰变中已经看到了这样的边带，但从未在自电离过程中观察到过。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。