Quantitative Measurements of Relativistic Electron Ejection from the Focus of Petawatt Lasers

该奖项支持测量高功率激光强度的技术发展。高功率激光器的发展能够在小体积内提供极高的强度，这使得科学界进入了一个实验研究的新时代。利用激光从真空中创造物质或揭示暗物质只是未来十年可能实现的两个例子。抑制这类研究进展和限制激光技术进步的一个主要障碍是，在全功率下实时测量聚焦高功率激光强度的可靠方法。该项目致力于开发方法，使这些测量能够直接部署并广泛适用于全国和世界各地的实验室。从产生新型光源到探测热致密物质到开发基于激光的医疗应用等一系列研究也将从该项目中受益匪浅。该项目强调国际参与，致力于吸纳科学、技术、工程和数学领域代表性不足的个人，提供了急需的能力，同时培养了多样化的学生骨干。在实现百瓦级和多百瓦级精确测量的过程中，阻碍进展的一个主要障碍是，在全功率下直接评估激光聚焦体积的任务看似简单，但却极其困难，例如测量激光束的强度和可视化畸变。该项目致力于开发一种评估程序，该程序具有以下特点：(i)实施简单，无需进行重大实验部署；（ii）干扰最小，允许不受限制地进行初级实验；（iii）对光束特性变化敏感，这种变化可能会降低焦点从一个镜头到另一个镜头的能量；（iv）单镜头能力。实现这种测量的一个有希望的机制是众所周知的质动机散射过程。在拍瓦级激光的焦点中产生的电子被加速并射出。由于能量和角度分布与焦点的强度分布密切相关，因此本项目旨在测量喷射能量并成像电子轨迹的角度分布。这种测量与数值模拟相结合，将能够确定峰值强度和焦点光斑的非理想性。该项目包括与世界各地的高功率激光设施直接合作，包括罗切斯特大学的激光能量学实验室（LLE）和英国的中央激光设施（CLF）。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This award supports development of techniques to measure the intensity of very high power laser light. The development of high-powered lasers capable of delivering extreme intensities into a small volume has placed the scientific community at the threshold of a new era for experimental investigation. Exploiting lasers to create matter out of vacuum or to shed light on dark matter are just two examples of what may become possible over the next decade. A major impediment inhibiting progress in such investigations, and constraining advancement of laser technology, is a reliable way to measure the intensity of a focused high-powered laser in real time at full power. This project is devoted to developing methodologies to enable such measurements that are straightforward to deploy and broadly applicable in laboratories across the country and around the world. A host of studies ranging from generating novel light sources to probing warm dense matter to developing laser-based medical applications will also benefit greatly from this project. Together with the emphasis on international engagement and a commitment to inclusion of underrepresented individuals in science, technology, engineering, and mathematics, this project provides a much-needed capability while training a diverse cadre of students.A major roadblock inhibiting progress towards realizing precision measurement at the petawatt and multi-petawatt level is the seemingly simple, but extremely difficult, task of assessing laser's focal volume directly at full power – such as measuring the intensity and visualizing distortions in the laser beam. This project is devoted to developing an assessment procedure that is (i) straightforward to implement without requiring a major experimental effort to deploy, (ii) minimally intrusive, allowing the primary experiment to be performed uninhibited, (iii) sensitive to beam characteristic changes that can degrade the energy in the focus from shot to shot, and (iv) single-shot capable. A promising mechanism for enabling such measurements is the well-known process of ponderomotive scattering. Electrons born in the focus of a petawatt-class laser are accelerated and ejected. Because the energy and angular distribution depend intimately on the intensity distribution in the focus, this project aims to measure the ejected energies and image the angular distributions of the electron trajectories. Such measurements coupled with numerical simulations will enable determination of the peak intensity and the non-ideality of the focal spot. The project includes direct engagement with high-power laser facilities worldwide, including the Laboratory for Laser Energetics (LLE) at the University of Rochester and the Central Laser Facility (CLF) in the United Kingdom.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.