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Intense Sub-Femtosecond Optical Radiation from Relativistic Plasmas

来自相对论等离子体的强亚飞秒光辐射

基本信息

批准号：
1619582
负责人：
Howard Milchberg
金额：
$ 46万
依托单位：
University of Maryland, College Park
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2016
资助国家：
美国
起止时间：
2016-08-01 至 2021-07-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1619582&HistoricalAwards=false
关键词：
Intense Sub Femtosecond Optical Radiation

项目摘要

This work will explore the shortest duration optical flashes ever generated, produced by accelerating electrons from rest to almost the speed of light over a distance less than one-hundredth the thickness of a human hair. The accelerating charged particles are produced by the interaction of low energy (but very high intensity) laser pulses with dense jets of hydrogen gas. The hydrogen gas has all of its electrons stripped off by the laser pulse, forming a plasma, and radiation pressure from the laser pulse then pushes the free electrons out of the way. This produces an electrostatic disturbance that moves as a wave in the plasma (a 'plasma wave') and is so strong that it can accelerate its own electrons from rest to nearly the speed of light in the form of directed beams. These beams of accelerated electrons are useful for medical and scientific imaging. One of their intriguing, exciting, and potentially useful byproducts is radiation flash emission, which takes place over just one half cycle of the radiation emission itself, making it of sub-femtosecond duration (less than 1/1000000000000000 second long). Such a light source, in addition to its fascinating internal relativistic dynamics, can act as the fastest-ever optical strobe source for capturing images, for example, of electrons in mid-flight in their orbits in an atom.This project will develop and characterize a new source of intense, coherent, sub-femtosecond pulses (or flashes) in the optical range. These pulses arise directly from wave breaking of relativistic plasma waves and are only indirectly driven by a pump laser field. The radiation flash appears to arise purely from classical acceleration of charged particles exposed to the enormous electric and magnetic fields inside relativistic plasma waves. Their spectral and coherence characteristics are strongly affected by the plasma density, which sets the group velocity of the plasma waves, the spatial scale of the radiating bunches, and the laser energy required for relativistic self-focusing of the initiating laser pulse. Such flashes are consistent with unidirectional acceleration of electrons from rest to nearly the speed of light. The project will consist of detailed measurements of flash coherence properties, temporal pulse structure, and exploration of timing control of this radiation. Accompanying the experiments will be extensive 2D and 3D particle-in-cell simulations. A new 1 kHz, 10 mJ laser system will enable experiments at a much higher repetition rate, improving shot-to-shot reproducibility and allowing high data collection rates, both of which lead to better signal-to-noise and more precise measurements.

这项工作将探索有史以来产生的持续时间最短的光学闪光，通过在不到人类头发厚度的百分之一的距离内将电子从静止加速到接近光速而产生。加速带电粒子是由低能量（但强度非常高）的激光脉冲与密集的氢气射流相互作用产生的。氢气的所有电子都被激光脉冲剥离，形成等离子体，然后激光脉冲的辐射压力将自由电子推开。这就产生了一种静电扰动，这种扰动在等离子体中以波的形式运动（“等离子体波”），并且它的强度如此之大，以至于它可以以定向光束的形式将自己的电子从静止加速到接近光速。这些加速电子束对医学和科学成像很有用。它们的一个有趣的、令人兴奋的、潜在有用的副产品是辐射闪光，它只发生在辐射发射本身的半个周期内，使得它的持续时间为亚飞秒（少于1/1000000000000000秒）。这样的光源，除了其迷人的内部相对论动力学外，还可以作为有史以来最快的光学频闪源，用于捕捉图像，例如，在原子轨道上飞行中的电子。该项目将在光学范围内开发和表征一种新的强、相干、亚飞秒脉冲（或闪光）源。这些脉冲直接产生于相对论性等离子体波的破波，仅由泵浦激光场间接驱动。辐射闪光似乎纯粹是由暴露在相对论等离子体波内部巨大的电场和磁场中的带电粒子的经典加速引起的。等离子体密度决定了等离子体波的群速度、辐射束的空间尺度和起始激光脉冲相对论性自聚焦所需的激光能量，对等离子体波的光谱和相干特性有很大的影响。这种闪光与电子从静止加速到接近光速的单向加速是一致的。该项目将包括对闪光相干特性、时间脉冲结构的详细测量，以及对这种辐射的定时控制的探索。伴随实验的将是广泛的二维和三维细胞内粒子模拟。一种新的1khz， 10mj激光系统将使实验具有更高的重复率，提高了射击到射击的再现性，并允许高数据收集率，这两者都导致更好的信噪比和更精确的测量。