RUI: A Study of Laser-Assisted Electron-Atom Scattering

这项工作旨在回答这样一个问题：当一个电子（所有原子的基本组成部分之一）在激光的存在下从原子或分子散射出去时会发生什么？可能发生的最简单的一类事情是“弹性散射”，在这种情况下，电子和原子在碰撞后不交换能量，而是以碰撞前的能量继续前进（但可能改变它们的方向）。这些过程被称为激光辅助自由-自由（LAFF）过程，因为电子在碰撞前后都是自由的（即不被原子或分子束缚）。这项工作将涉及实验性LAFF研究，其广泛目标是增加我们对这些过程的基本理解。将特别注意解决理论和实验之间长期存在的差异（有几组实验数据已经违背理论解释超过二十年），并研究双色激光场如何影响和可以用来控制散射过程。除了提高我们对散射过程的基本认识外，这项工作还可以应用于各种领域，包括基础和应用领域。例如，类似的过程对于理解恒星的内部和大气非常重要。自由-自由跃迁在放电中发生的气体分解中也起着重要作用，并为激光加热等离子体（电离原子气体）提供了一种方法。了解这些过程有助于为等离子体物理学领域奠定更坚实的科学基础，等离子体物理学是计算机和手机核心微电子制造的基础。这项工作将主要在一所本科院校进行，并将直接涉及几名本科生的研究。为了实现上述目标，将进行两组不同的LAFF实验研究。第一组实验将继续这个小组以前的工作，理论很好地描述了这一点，尽管另一个小组做的一些类似的实验与当前的理论理解相矛盾。两组实验有三个显著差异：电子能量、光子能量和光子偏振。新的实验将研究一系列的入射能量，以及以前没有研究过的几何形状；例如，激光传播方向垂直于散射面，激光偏振方向垂直于散射面。本质上，实验将会从微扰状态，变为非微扰状态。这些数据将检验当前的理论，并为LAFF过程更复杂的理论描述的发展提供见解。此外，新的实验将在使用双色（光子能量= 1.17 eV和2.34 eV）激光场的LAFF实验中寻找干涉效应。在这种双色场中散射的能量低于弹性峰值2.34 eV的电子可能发射一个2.34 eV的光子或两个1.17 eV的光子。研究小组将进行实验，改变这两种颜色的相对相位，以观察预测的干涉效应。

This work aims to answer the question: what happens when an electron (one of the fundamental building blocks of all atoms) scatters from an atom or molecule in the presence of light from a laser? One of the simplest classes of things that can happen is "elastic scattering" in which the electron and the atom do not exchange energy and continue on their way after the collision with the same energies that they had before the collision (but perhaps changing their direction). These are called laser-assisted free-free (LAFF) processes because the electron is free (i.e., not bound to an atom or molecule) both before, and after, the collision. This work will involve experimental LAFF studies, with the broad aim of increasing our basic understanding of these processes. Particular attention will be paid to resolving long-standing discrepancies between theory and experiment (there are several sets of experimental data that have defied theoretical explanation for over twenty years) and examining how two-color laser fields affect, and can be used to control, scattering processes. In addition to the advancement of our basic understanding of scattering processes, this work has applications to a variety of fields, both basic and applied. For example, similar processes are important for understanding the interiors and atmospheres of stars. Free-free transitions also play a major role in the gas breakdown that occurs in electrical discharges, and provide a method for laser heating of a plasma (a gas of ionized atoms). Understanding these processes helps form a more solid scientific foundation for the field of plasma physics which underlies the manufacturing of the microelectronics at the heart of our computers and cell phones. This work will primarily take place at an undergraduate institution, and will directly involve several undergraduate students in research.To accomplish the above stated aims, two different sets of experimental LAFF studies will be performed. The first set of experiments will continue this group's previous work which is well described by theory in spite of the fact that some similar experiments done by another group contradict current theoretical understanding. There are three significant differences between the experiments performed by the two groups: the electron energy, the photon energy, and the photon polarization. The new experiments will investigate a range of incident energies, as well as geometries that have not previously been investigated; e.g., laser propagation direction perpendicular to the scattering plane, and laser polarization direction perpendicular to the scattering plane. Essentially, the experiments will go from perturbative, to non-perturbative regimes. This data will test current theory, as well as provide insight to the development of more complex theoretical descriptions of the LAFF processes. In addition, the new experiments will look for interference effects in LAFF experiments that use a two-color (photon energy = 1.17 eV, and 2.34 eV) laser field. Electrons scattered in such a two-color field that have an energy 2.34 eV below the elastic peak may have emitted either a single 2.34 eV photon or two 1.17 eV photons. The research group will perform experiments that vary the relative phase of these two colors to observe predicted interference effects.