Singh P K, Li F-Y, Huang C-K, Moreau A, Hollinger R, Junghans A, Favalli A, Calvi C, Wang S, Wang Y, Song H, Rocca J J, Reinovsky R E, Palaniyappan S
Los Alamos National Laboratory, Los Alamos, NM, 87545, USA.
Department of Electrical and Computer Engineering, Colorado State University, Fort Collins, CO, 80523, USA.
Nat Commun. 2022 Jan 10;13(1):54. doi: 10.1038/s41467-021-27691-w.
Intense lasers can accelerate electrons to very high energy over a short distance. Such compact accelerators have several potential applications including fast ignition, high energy physics, and radiography. Among the various schemes of laser-based electron acceleration, vacuum laser acceleration has the merits of super-high acceleration gradient and great simplicity. Yet its realization has been difficult because injecting free electrons into the fast-oscillating laser field is not trivial. Here we demonstrate free-electron injection and subsequent vacuum laser acceleration of electrons up to 20 MeV using the relativistic transparency effect. When a high-contrast intense laser drives a thin solid foil, electrons from the dense opaque plasma are first accelerated to near-light speed by the standing laser wave in front of the solid foil and subsequently injected into the transmitted laser field as the opaque plasma becomes relativistically transparent. It is possible to further optimize the electron injection/acceleration by manipulating the laser polarization, incident angle, and temporal pulse shaping. Our result also sheds light on the fundamental relativistic transparency process, crucial for producing secondary particle and light sources.
强激光能在短距离内将电子加速到非常高的能量。这种紧凑型加速器有多种潜在应用，包括快点火、高能物理和射线照相。在各种基于激光的电子加速方案中，真空激光加速具有超高加速梯度和极大简易性的优点。然而，由于将自由电子注入快速振荡的激光场并非易事，其实现一直很困难。在此，我们利用相对论透明效应演示了自由电子注入以及随后将电子真空激光加速至20兆电子伏特。当高对比度强激光驱动薄固体箔时，来自致密不透明等离子体的电子首先被固体箔前方的驻波激光加速到接近光速，随后随着不透明等离子体变得相对论性透明而被注入到透射激光场中。通过操纵激光偏振、入射角和时间脉冲整形，有可能进一步优化电子注入/加速。我们的结果也为基本的相对论透明过程提供了启示，这对于产生次级粒子和光源至关重要。
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