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种激光焦点附近的光场。 在这种极端的光中，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（万亿亿）g的速度加速电子，其中一个g是由于地球上的重力而产生的加速度。 自由电子然后被推进到非常接近光速的速度，因此爱因斯坦的相对论方程需要描述它们的运动。 在这些极端条件下，电子将波长偏移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了一种技术，可以将散射的光子与驱动电子的激光脉冲中的五次方背景光子区分开来。 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。 这样的激光焦点以任何其他方式表征都是具有挑战性的，因为焦点通常与相机上的单个像素一样小。 此外，在全功率下，任何放置在焦点上的相机都会被摧毁。 对非常强烈但微小的激光焦点内的电场和磁场进行分析，将有助于理解激光与原子、分子和固体之间的相互作用，这些都是用世界上最强大的激光进行研究的。 该项目还将为学生提供光学和光子学技术培训的机会，并为基础科学的进步做出贡献。测量激光焦点中仅几个电子散射的单个光子的能力使在非常低的密度（基本上是真空）下观察基本相对论现象成为可能。 这将使该团队能够避免在更高密度下发生的等离子体动力学的混淆影响。 他们将研究非线性汤姆逊散射的偏振在空间分布的散射的基本，第二和第三谐波光。 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。 极化分辨散射图中丰富的结构预示着对电子动力学的新见解。该团队对激光聚焦内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。使用可变形镜将允许他们创建理想的和奇异的焦点形状，以测试非线性汤姆逊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.