Concurrence of monoenergetic electron beams and bright X-rays from an evolving laser-plasma bubble
Concurrence of monoenergetic electron beams and bright X-rays from an evolving laser-plasma bubble
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单能电子束和来自不断演化的激光等离子体气泡的明亮 X 射线同时发生
DOI：
10.1073/pnas.1404336111
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发表时间：
2014
影响因子：
11.1
通讯作者：
Zhang Jie
中科院分区：
文献类型：
--
作者：
Yan Wenchao;Chen Liming;Li Dazhang;Zhang Lu;Hafz Nasr A. M.;Dunn James;Ma Yong;Huang Kai;Su Luning;Chen Min;Sheng Zhengming;Zhang Jie
桌面激光等离子体加速能够产生单能电子束，电子束在等离子体泡中振荡，产生具有飞秒时间分辨能力的准直X射线。然而，高通量的X射线发射和高质量的电子束还没有同时获得，因为高产量的X射线发射通常是在电子束质量的成本。通过对等离子体泡的两次注入，我们观测到了千兆电子伏级的单能电子束和峰值亮度高于第三代同步加速器的超强硬X射线。由于固有的时间同步，这种独特的电子光子源可以是理想的“单次”泵浦探测应用在飞秒和纳米尺度。台式激光等离子体加速已被证明能够产生千兆电子伏级准单能电子束。此外，这种电子束可以在激光产生的等离子体泡/通道中横向振荡（摆动运动），并发射被称为电子感应加速器辐射的准直超短X射线闪光，其光子能量范围从千电子伏到兆电子伏。这意味着通常不能在同一加速波桶中同时获得明亮的电子感应加速器X射线和具有低发射度和小能量扩展的高质量电子束。在这里，我们报告的第一个（据我们所知）实验观察到两个不同的电子聚束在一个单一的激光射击，一个具有准单能谱，另一个具有连续谱沿着与大发射度。后者能够产生高通量的电子感应加速器X射线。只有当激光自导引在固定的等离子体密度（4 × 1018 cm−3）下延伸超过4 mm时，才能观察到这种现象。数值模拟表明，由于气泡的演化，两束电子在不同的阶段被注入。第一束团在开始时注入，形成稳定的准单能电子束，而第二束团在传输过程中由于激光光斑尺寸的变化而引起气泡尺寸的振荡，因此在稍后注入。由于固有的时间同步性，这种独特的电子光子源可以是具有飞秒时间分辨率的泵浦探测应用的理想选择。
Significance Desktop laser plasma acceleration is able to generate monoenergetic electron beams, and such electron beams can oscillate in the plasma bubble, which results in the collimated X-rays with ability of femtosecond temporal resolution. However, high-flux X-ray emission and high-quality electron beams have not been obtained simultaneously because high-yield X-ray emission is usually produced at the cost of electron beam qualities. By stimulating double injections into a plasma bubble, we report our experimental observation in which both a monoenergetic electron beam at the gigaelectronvolt level and ultraintense hard X-rays with peak brightness higher than the third generation of synchrotrons. Due to the inherent temporal synchronization, this unique electron–photon source can be ideal for “single-shot” pump–probe applications at femtosecond and nanometer scales. Desktop laser plasma acceleration has proven to be able to generate gigaelectronvolt-level quasi-monoenergetic electron beams. Moreover, such electron beams can oscillate transversely (wiggling motion) in the laser-produced plasma bubble/channel and emit collimated ultrashort X-ray flashes known as betatron radiation with photon energy ranging from kiloelectronvolts to megaelectronvolts. This implies that usually one cannot obtain bright betatron X-rays and high-quality electron beams with low emittance and small energy spread simultaneously in the same accelerating wave bucket. Here, we report the first (to our knowledge) experimental observation of two distinct electron bunches in a single laser shot, one featured with quasi-monoenergetic spectrum and another with continuous spectrum along with large emittance. The latter is able to generate high-flux betatron X-rays. Such is observed only when the laser self-guiding is extended over 4 mm at a fixed plasma density (4 × 1018 cm−3). Numerical simulation reveals that two bunches of electrons are injected at different stages due to the bubble evolution. The first bunch is injected at the beginning to form a stable quasi-monoenergetic electron beam, whereas the second one is injected later due to the oscillation of the bubble size as a result of the change of the laser spot size during the propagation. Due to the inherent temporal synchronization, this unique electron–photon source can be ideal for pump–probe applications with femtosecond time resolution.