RUI: Studying Fundamental Electron-Photon Interactions with an Ultrafast Electron Microscope

在过去的十年里，将电子显微镜和超快激光相结合形成了一个新的研究领域。现在，“超快电子显微镜”可以用来拍摄纳米(微观)过程的电影，这些过程发生得太快，用标准的电子显微镜无法观察到。这个项目将使用超快电子显微镜来研究基本的量子力学现象，如轨道角动量从光到电子的转移。该团队还将探索如何利用光在皮秒到几十飞秒的时间内压缩电子脉冲，并塑造电子束的空间属性。本科生将获得使用低能超快电子显微镜进行这些实验的研究经验，这种培训将有助于他们为深造或在高科技行业工作做准备。作为对社会的另一种益处，这些实验将展示新的光学操纵方法，以控制纳米和飞秒精度的电子脉冲，这反过来将提高电子显微镜的技术能力。该项目将探索有效控制短电子脉冲空间和时间特性的新技术。第一种技术将使用Kapitza-Dirac效应将轨道角动量从光子转移到电子，使两个不同自由粒子之间的轨道角动量能够量化转移。这项实验的成功演示将表明，光可以用来操纵电子束的空间位相。将探索的第二种技术是使用强烈的驻波光将电子脉冲从皮秒持续时间压缩到只有几飞秒。目前用于超快电子衍射和显微镜的电子脉冲被限制在大约100飞秒，这使得各种动态过程变得遥不可及。持续时间为几飞秒的电子脉冲将提供跟踪结构和电子纳米级系统中的动态过程的机会。总而言之，这个项目将展示用新方法控制电子脉冲的空间和时间属性，这些方法可以对物理、化学和生物学所需的成像和量子控制技术产生影响。

Over the last decade a new research field has developed by combining electron microscopy with ultrafast lasers. Now "ultrafast electron microscopes" can be used to make movies of nanoscale (microscopic) processes that occur too quickly to observe with standard electron microscopes. This project will use an ultrafast electron microscope to study fundamental quantum mechanical phenomena such as the transfer of orbital angular momentum from light to electrons. This team will also explore how light can be used to compress electron pulses in time from picoseconds to tens of femptoseconds, and to shape the spatial properties of electron beams. Undergraduate students will gain research experience conducting these experiments with a low-energy ultrafast electron microscope, and this training will help prepare them for advanced studies or jobs in high tech industry. As another benefit to society, these experiments will demonstrate novel optical manipulation methods to control electron pulses with nanometer and femtosecond precision, and this in turn will advance the technical capabilities of electron microscopes.This project will explore new techniques to efficiently control the spatial and temporal properties of short pulses of electrons. The first technique will use the Kapitza-Dirac effect to transfer orbital angular momentum from photons to electrons, enabling quantized transfer of orbital angular momentum between two different free particles. A successful demonstration of this experiment will show that light can be used to manipulate the spatial phase of an electron beam. The second technique that will be explored is the use of intense standing waves of light to compress electron pulses from picosecond durations to only a few femtoseconds. Current electron pulses used for ultrafast electron diffraction and microscopy are limited to about 100 femtoseconds, which leaves a variety of dynamical processes out of reach. Electron pulses with durations of a few femtoseconds will provide an opportunity to follow dynamical processes in structural and electronic nanoscale systems. In summary, this project will demonstrate control over the spatial and temporal properties of electron pulses with novel methods that can have an impact on imaging and quantum control techniques that are needed for physics, chemistry, and biology.