RUI: Image-Based Strong-Field Adaptive Control of Molecular Dynamics

非技术描述：传统的化学合成方法类似于烹饪，因为配料、混合方法、温度和压力都可以改变以产生期望的结果。尽管可以控制所有这些宏观变量，但仍有一些化学过程是难以捉摸的。自20世纪60年代激光发明以来，相干控制领域一直在寻求利用激光通过将适当颜色和持续时间的能量直接应用于单个分子来操纵化学动力学。从这个意义上说，激光可以被认为是一种驱动化学反应的新型试剂。虽然说得很简单，但事实证明这项任务具有挑战性。分子是复杂和动态的，因此很难确定正确的激光特性来驱动特定的过程。解决这一问题的一种行之有效的方法是利用实验反馈来指导对可能的激光脉冲的自适应搜索。在自然选择的物理版本中，提供更好结果的激光脉冲被赋予了更大的生存机会，并且它们的特性有助于最终产生理想结果的定制脉冲。然而，这种方法的效果取决于驱动它的反馈。这些研究的目标是开发增强的基于图像的反馈技术，使这种自适应方法能够连贯地控制化学动力学。技术描述：PI最近开发了使用激光分子反应产物的三维动量成像来定义上述非技术描述中描述的控制目标的能力。使用三维成像来定位特定的最终状态，可以更好地理解基于激光控制的机制，特别是在无法获得精确的光谱反馈的情况下。增加对机制的理解可以导致更好的搜索参数化，从而增强自适应控制过程。目前的研究重点是应用基于图像的自适应控制来研究和影响乙烯等小分子的光异构化过程。通过研究光电离，有可能探索电子激发如何迅速转化为核运动，这是许多超快化学过程的重要步骤。乙烯是一个特别有趣的基准分子，用于研究在这些电子到核能的转换过程中锥形交叉点的作用。这些研究将通过使用双脉冲实验来推进，该实验允许将电离步骤与分子离子的后续进化分离，该小组希望控制电离步骤。多原子分子的强场隧道电离通常涉及多个分子轨道，对这些关系的研究有助于将基于图像的反馈与更具体的目标状态联系起来，再次以改进自适应控制方法为目的。本项目的目标是扩展这项工作，探索通过角度分辨光电子分布的反馈来控制激光驱动的电子再散射。电子重散射是许多基于超快激光的过程的重要组成部分，例如高谐波产生和阿秒脉冲的产生，因此这种类型的控制具有许多潜在的应用。最后，作为一个本科院校，这个项目通过让学生沉浸在前沿研究中，帮助发现和培养有才华的学生。

Non-technical description:Traditional chemical synthesis methods resemble cooking in the sense that the ingredients, mixing methods, temperature, and pressure all may be varied to produce a desired result. Despite control over all of these macroscopic variables there are some chemical processes that remain elusive. Since the invention of the laser in the 1960s, the field of coherent control has sought to use the laser to manipulate chemical dynamics by applying energy of suitable color and duration directly to individual molecules. In this sense, the laser can be thought of as a new type of reagent that drives a chemical reaction. While easily stated, this task has proved challenging. Molecules are complicated and dynamic, making it difficult to determine the correct laser characteristics to drive a particular process. A proven method for approaching this problem is to use experimental feedback to guide an adaptive search of the possible laser pulses. In a physics version of natural selection, laser pulses that provide a better outcome are given an increased chance to survive and have their characteristics contribute to the tailored pulse that ultimately produces the desired outcome. Such a method, however, is only as good as the feedback that drives it. The goal of these studies is to develop enhanced image-based feedback techniques that enable this adaptive approach to coherent control of chemical dynamics. Technical description:The PI has recently developed the ability to use three-dimensional momentum imaging of the laser-molecule reaction products to define the control objective described in the non-technical description above. Using three-dimensional imaging to target a specific final state has led to better understanding of the mechanisms that undergird the laser-based control, especially in situations in which obtaining precise optical spectroscopic feedback is impractical. Increased mechanistic understanding can subsequently lead to better search parameterization, enhancing the adaptive control process. Current efforts are focused on applying image-based adaptive control to study and influence photoisomerization processes in small molecules such as ethylene. By studying photoionization, it is possible to probe how electronic excitation is rapidly converted to nuclear motion, an essential step in many ultrafast chemical processes. Ethylene is particularly interesting as a benchmark molecule for examining the role of conical intersections in these electronic to nuclear energy conversions. These studies will be advanced by using two-pulse experiments, which allow the separation of the ionization step from the subsequent evolution of the molecular ion, which the group hopes to control. Strong-field tunneling ionization of polyatomic molecules often involves multiple molecular orbitals, and studies of these relationships help link the image-based feedback to more specific target states, again with the objective of refining adaptive control methods. A goal of this project will be extending this work to explore the control of laser driven electron rescattering via feedback derived from angle resolved photoelectron distributions. Electron rescattering is an essential part of many ultrasfast laser-based processes, such as high-harmonic generation and the production of attosecond pulses, and therefore control of this sort has a number of potential applications. Finally, as an undergraduate institution, this project helps identify and develop talented students by immersing them in forefront research.