Coherent synchrotron emission from electron nanobunches formed in relativistic laser-plasma interactions
Coherent synchrotron emission from electron nanobunches formed in relativistic laser-plasma interactions
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DOI：
10.1038/nphys2439
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发表时间：
2012-11-01
期刊：
影响因子：
19.6
通讯作者：
Hegelich, B. M.
中科院分区：
文献类型：
--
作者：
Dromey, B.;Rykovanov, S.;Hegelich, B. M.
到目前为止，由强激光-固体相互作用产生的极紫外（XUV）和X射线谐波光谱与集体相对论等离子体振荡-相对论振荡镜机制（1-6）的多普勒上移反射一致。然而，最近的理论工作已经确定了一种新的相互作用机制，其中在等离子体-真空边界处形成密集的电子纳米束，从而通过相干同步辐射（7，8）（CSE）产生相干XUV辐射。我们的实验使CSE从竞争过程中分离出来，表明电子纳米束的形成确实发生了。我们观察到具有CSE特征光谱特征的光谱-强度I的缓慢衰减，具有高谐波阶数n，因为I（n）在快速效率翻转之前与n（-1.62）成比例。粒子在细胞的代码模拟揭示了如何密集的纳米束的电子周期性地形成和加速在正常的入射相互作用与反射箔，并导致在CSE的传输方向。对CSE的观察为高能XUV脉冲提供了一条途径（7，8），并为理解强激光-固体密度相互作用期间的超快能量耦合提供了一个新的窗口。
Extreme ultraviolet (XUV) and X-ray harmonic spectra produced by intense laser-solid interactions have, so far, been consistent with Doppler upshifted reflection from collective relativistic plasma oscillations-the relativistically oscillating mirror mechanism(1-6). Recent theoretical work, however, has identified a new interaction regime in which dense electron nanobunches are formed at the plasma-vacuum boundary resulting in coherent XUV radiation by coherent synchrotron emission(7,8) (CSE). Our experiments enable the isolation of CSE from competing processes, demonstrating that electron nanobunch formation does indeed occur. We observe spectra with the characteristic spectral signature of CSE-a slow decay of intensity, I, with high-harmonic order, n, as I(n) proportional to n(-1.62) before a rapid efficiency rollover. Particle-in-cell code simulations reveal how dense nanobunches of electrons are periodically formed and accelerated during normal-incidence interactions with ultrathin foils and result in CSE in the transmitted direction. This observation of CSE presents a route to high-energy XUV pulses(7,8) and offers a new window on understanding ultrafast energy coupling during intense laser-solid density interactions.