Polarization-Resolved Single-Photon Measurements of Nonlinear Thomson Scattering

激光技术的进步使得在激光束聚焦的微小区域内产生异常明亮的光成为可能。该项目将开发一种新的方法来研究这样一个激光焦点附近的光场。在如此极端的光线下，电场和磁场可以将电子从任何物质中剥离出来，然后以超过六万亿克的速度加速电子，其中一克是地球引力所产生的加速度。然后，被释放的电子被推进到非常接近光速的速度，因此需要爱因斯坦的相对论方程来描述它们的运动。在这些极端情况下，电子将波长移位的光散射出激光焦点(称为非线性汤姆逊散射)，这可以揭示电子运动的动力学，从而揭示激光场的结构。这个研究小组已经开发出技术来区分散射的光子和组成驱动电子的激光脉冲的亿万个背景光子。在这个项目中，该团队将使用散射光作为探测器来绘制焦点内和周围光场的强度和偏振。这样的激光焦点很难用任何其他方式来表征，因为焦点通常只有相机上的一个单独像素那么小。此外，在最大功率的情况下，任何放置在焦距上的相机都将被摧毁。分析一个非常强但很小的激光焦点内的电场和磁场，将有助于理解激光与世界上最强大的激光研究的原子、分子和固体之间的相互作用。这个项目还将为学生提供一个机会，让他们接受光学和光子学技术的培训，促进基础科学的进步。测量激光焦点中仅由几个电子散射的单个光子的能力，使人们能够在极低密度(基本上是真空)下观察基本的相对论现象。这将使该团队能够避免在较高密度下发生的等离子体动力学的混杂影响。他们将研究散射基波、二次和三次谐波光空间分布中的非线性汤姆逊散射的偏振。极化包含一个额外的信息维度，这是以前没有研究或测量过的。偏振分辨散射图中丰富的结构为我们提供了对电子动力学的新见解。该团队对紧密激光焦点内的相对论电子轨迹的模拟表明，电子轨迹对激光场矢量的细节很敏感。可变形反射镜的使用将使他们能够创造出理想的和奇异的焦点形状，以测试非线性汤姆森散射对焦点中矢量场分布细节的敏感性。

Advances in laser technology have made it possible to create exceptionally bright light inside a tiny region where a laser beam is focused. This project will develop a new way to study the optical fields near such a laser focus. The electric and magnetic fields in such extreme light can rip electrons away from any substance and then accelerate the electrons at more than sextillion (thousand billion billion) g's, where one g is the acceleration due to gravity on Earth. The freed electrons are then propelled to very near the speed of light, so Einstein's equations of relativity are required to describe their motion. Electrons under these extreme conditions scatter wavelength-shifted light out of the laser focus (called nonlinear Thomson scattering), and this can reveal the dynamics of the electron motion and thus the structure of the laser fields. This research team has developed techniques to distinguish the scattered photons from the quintillion background photons that comprise the laser pulse that drives the electrons. With this project, the team will use the scattered light as a probe to map the strength and polarization of the optical fields in and around the focus. Such a laser focus is challenging to characterize in any other way, since the focus is often as small as an individual pixel on a camera. Furthermore, at full power any camera placed in the focus would be destroyed. Analysis of the electric and magnetic fields inside a very intense but tiny laser focus will be helpful for understanding interactions between laser light and atoms, molecules, and solids that are studied with the world's most powerful lasers. This project will also provide an opportunity for students to be trained on optics and photonics technologies and contribute to progress in fundamental science.The ability to measure individual photons scattered from only a few electrons in a laser focus enables observation of fundamental relativistic phenomena at very low densities (essentially a vacuum). This will allow this team to avoid the confounding influence of plasma dynamics that occur for higher densities. They will study the polarization of nonlinear Thomson scattering in the spatial distribution of the scattered fundamental, second, and third harmonic light. The polarization contains an added dimension of information, which has not previously been investigated or measured. The rich structure in polarization-resolved scattering plots promises new insights into electron dynamics. This team's simulations of relativistic electron trajectories within a tight laser focus show that electron trajectories are sensitive to the details of the field vectors of the laser. The use of a deformable mirror will allow them to create ideal and exotic focal shapes to test the sensitivity of nonlinear Thomson scattering to the details of the vector field distributions in the focus.