Holographic Imaging of Evolving Laser-Plasma Structures

该奖项是对提交给NSF/美国能源部基础等离子体科学与工程伙伴关系联合征集NSF 09-596的提案的回应。该奖项为本科生参与整个研究工作提供资金，该研究工作由美国能源部根据与德克萨斯大学的合同单独提供资金(Grant DE-FG02-07ER54945)。当强烈的飞秒激光脉冲或电子束通过电离气体或等离子体传播时，它们会取代其包层内的等离子体电子，就像船在湖中传播时取代水一样。因此，它们产生了以光速传播的电子密度结构，并随着它们的传播而演变成形状，就像船后面的尾迹一样。近年来，科学家们开发了微型粒子加速器，这种加速器通过在这些电子密度波上冲浪带电粒子来工作。然而，加速器的性能很难优化，因为波结构是看不见的，除非通过密集的计算机模拟间接地进行，而且控制起来很困难。该项目将开发可视化和控制这些光速结构的方法。为了将它们可视化，三项任务中的第一项旨在开发一种频域断层成像(FDT)系统，该系统将拍摄由一次激光发射产生的不断演变的等离子体结构的多帧“电影”。FDT系统将多路传输现有的频域全息系统，该系统在以前的工作中开发，使用与不断演变的结构共同传播并重叠的单个探测脉冲来拍摄略微模糊的“快照”。新的FDT系统在等离子体结构中增加了以倾斜角度传播的探测器。类似于医学CAT扫描中使用的断层扫描算法，然后将重建描述等离子体结构演变不同阶段的多个“帧”。在三项任务中的第二项任务中，可视化技术将扩展到电子束驱动的等离子体尾迹，在布鲁克海文国家实验室的高级测试设施(ATF)进行的一项实验中，该实验最近经ATF项目咨询委员会外部审查后获得批准。随着驱动束序列的形式和等离子体密度的变化，等离子体尾迹的时间和径向结构将被可视化。为了控制驱动激光脉冲及其产生的等离子体结构的演变，三项任务中的第三项引入了辅助驱动激光脉冲，该脉冲与主激光脉冲共同传播，并且在频率上相差大约电子等离子体频率。该项目的合作者之前开发的理论表明，这样的次级脉冲可以控制强驱动激光脉冲的传播，而由领头PI开发的双色太瓦激光系统产生实现此类实验所需的时间同步边带脉冲。该项目引入了独特的方法来可视化和控制快速发展的相对论激光-等离子体相互作用，这是共同PIS开创的。它将首次提供激光和电子束驱动的等离子体尾迹演变的实验室可视化，并将补充、基准和验证这些结构的计算机模拟。双色激光-等离子体相互作用提供了一种控制等离子体波传播的新方法，这一方法已经成熟到可以实验验证的程度。这里开发的对抗或增强相对论自聚焦的能力可以影响激光聚变的快速点火，并导致更可靠的等离子体加速器，进而用于紧凑型X射线源、传统加速器的注入器和医疗加速器。提出的双色激光等离子体相互作用的研究可能导致新一代基于等离子体的放大器和压缩器，用于超强激光脉冲，而不受材料损伤的限制。最后，这项拟议的研究将从德克萨斯大学圣安东尼奥分校培养一名博士后、三名博士生和一名本科生。圣安东尼奥分校授予拉美裔美国人的本科学位数量在全国排名第四。该项目由美国国家科学基金会和美国能源部共同资助。国家科学基金会对本科生参与的支持通过向学生介绍科学研究作为一条可能的职业道路，通过早期培训增加了更广泛的教育影响。

This award is made in response to a proposal submitted to and reviewed under the NSF/DOE Partnership in Basic Plasma Science and Engineering joint solicitation NSF 09-596. The award provides funds to support undergraduate participation in the overall research effort, which is being funded separately by the DOE under contract to University of Texas (Grant DE-FG02-07ER54945). When intense femtosecond laser pulses or electron bunches propagate through an ionized gas, or plasma, they displace plasma electrons from within their envelopes, much like a boat displaces water as it propagates through a lake. As a result, they produce electron density structures that propagate at the speed of light and evolve in shape as they propagate, like the wake behind a boat. In recent years, scientists have developed miniature particle accelerators that work by surfing charged particles on these electron density waves. However, the performance of the accelerators is difficult to optimize because the wave structures are invisible, except indirectly through intensive computer simulations, and challenging to control. This project will develop methods for visualizing and controlling these light-velocity structures. To visualize them, the first of three tasks aims to develop a Frequency Domain Tomography (FDT) system that will take multi-frame "movies" of evolving plasma structures created by a single laser shot. The FDT system will multiplex an existing Frequency Domain Holography system, developed in prior work, that takes slightly blurred "snapshots" using a single probe pulse that co-propagates with and overlaps the evolving structure. The new FDT system adds probes propagating at oblique angles to the plasma structure. Tomographic algorithms similar to those used in medical CAT scans will then reconstruct multiple "frames" depicting the plasma structure at different stages of its evolution. In the second of three tasks, the visualization techniques will be extended to electron-bunch-driven plasma wakes in an experiment at Brookhaven National Laboratory's Advanced Test Facility (ATF) that was recently approved by the ATF Program Advisory Committee after external review. The temporal and radial structure of the plasma wakes will be visualized as the format of the drive bunch train and the plasma density vary. To control evolution of the drive laser pulse and plasma structures it creates, the third of three tasks introduces a secondary drive laser pulse that co-propagates with the main laser pulse and differs in frequency by approximately the electron plasma frequency. Theory developed previously by the co-PI of this project showed that such a secondary pulse can control the intense drive laser pulse's propagation, while a two-color terawatt laser system developed by the lead PI produces temporally synchronized sideband pulses needed to implement such experiments. The project introduces unique approaches to visualizing and controlling rapidly evolving relativistic laser-plasma interactions that the co-PIs pioneered. It will provide the first laboratory visualization of evolving laser- and e-beam driven plasma wakes, and will complement, benchmark and validate computer simulations of these structures. Two-color laser-plasma interactions provide a new approach to controlling plasma wave propagation that is ripe for experimental demonstration.The ability to combat or enhance relativistic self-focusing developed here can impact fast ignition of laser fusion, and lead to more reliable plasma-based accelerators, useful in turn as compact x-ray sources, injectors for conventional accelerators, and medical accelerators. Proposed investigations of two-color laser plasma interactions can lead to a new generation of plasma-based amplifiers and compressors for ultra-intense laser pulses that are free of material damage limits. Finally the proposed research will train a postdoc, three Ph.D. students, and an undergraduate from UT-San Antonio, which ranks 4th in the nation in number of undergraduate degrees awarded to Hispanics.This project is jointly funded by the NSF and the DOE.The NSF support of undergraduate participation adds a broader educational impact through the early-year training of students by introducing them to scientific research as a possible career path.