RUI: Investigations of One- and Two-Color Laser-Assisted Electron Scattering

了解分子和材料的微观结构是理解它们的物理和化学性质以及它们的基本功能和技术应用的关键。然而，除了测量结构外，物理学家还试图了解在散射过程中电子和分子之间发生的相互作用。这些知识可以用来开发更灵敏的技术来确定结构，例如，当一个分子正在经历结构变化时。通过这些研究获得的知识还可以影响电子-原子-激光相互作用的应用，其中包括用于测量超快物理和化学过程的极紫外光短脉冲的产生。本研究的目的是了解在强激光场存在下的电子-原子散射，特别是原子和分子中的电子对强激光场的反应。没有激光场，最简单的事情就是电子和原子在碰撞后不交换能量，继续以碰撞前相同的能量前进，可能只改变方向。从激光中加入的光可以产生这样的弹性？散射电子吸收一定数量的光子，从而增加电子的能量，或者发射光子，从而降低电子的能量。这些过程被称为激光辅助自由-自由（LAFF）过程，因为电子是自由的，也就是说，在碰撞前后都没有被原子或分子束缚。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。在双色（光子能量分别为1.17 eV和2.34 eV）激光场的LAFF实验中，我们将特别关注寻找干涉效应，并将其用于控制散射过程。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，LAFF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。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。

Knowing the microscopic structures of molecules and materials is key to understanding their physical and chemical properties and therefore their basic functions and technological applications. However, in addition to measuring structures, which is widely carried out using electron scattering, physicists seek to understand the interactions that occur between electrons and molecules during the scattering process itself. This knowledge can then be used to develop more sensitive techniques for determining structures, for example, while a molecule is undergoing a structural change. Knowledge gained through these studies can also influence applications of electron-atom-laser interactions, which include the generation of short pulses of extreme ultraviolet light that are used to measure ultrafast physical and chemical processes. The goal of this research is to understand electron-atom scattering in the presence of an intense laser field, in particular, how electrons in atoms and molecules respond to intense fields. Without the laser field, the simplest thing that can happen is that 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, possibly changing only their direction. Addition of light from a laser can cause such ?elastically? scattered electrons to absorb some number of photons, which increases the energy of the electron, or emit photons, thereby reducing the electron's energy. 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 at looking for interference effects in LAFF experiments that use a two-color (photon energy = 1.17 eV, and 2.34 eV) laser field, and which might 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, LAFF 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 electric discharges, and provide a method for laser heating of a plasma (a gas of ionized atoms). This work will primarily take place at an undergraduate institution, and will directly involve several undergraduate students in research.