Liu Weihang, Feng Chao, Jiao Yi, Wang Sheng
China Spallation Neutron Source, Institute of High Energy Physics, Chinese Academy of Sciences, Dongguan, Guangdong 523803, People's Republic of China.
Shanghai Advanced Research Institute, Chinese Academy of Sciences, Shanghai 201210, People's Republic of China.
J Synchrotron Radiat. 2021 May 1;28(Pt 3):669-680. doi: 10.1107/S1600577521002745. Epub 2021 Mar 22.
The electron beam generated in laser plasma accelerators (LPAs) has two main initial weaknesses - a large beam divergence (up to a few milliradians) and a few percent level energy spread. They reduce the beam brightness and worsen the coherence of the LPA-based light source. To achieve fully coherent radiation, several methods have been proposed for generating strong microbunching on LPA beams. In these methods, a seed laser is used to induce an angular modulation into the electron beam, and the angular modulation is converted into a strong density modulation through a beamline with nonzero longitudinal position and transverse angle coupling. In this paper, an alternative method to generate microbunching into the LPA beam by using a seed laser that induces an energy modulation and transverse-longitudinal coupling beamlines that convert the energy modulation into strong density modulation is proposed. Compared with the angular modulation methods, the proposed method can use more than one order of magnitude lower seed laser power to achieve similar radiation performance. Simulations show that with the proposed method a coherent pulse of a few microjoules pulse energy and femtosecond duration can be generated with a typical LPA beam.
激光等离子体加速器（LPA）中产生的电子束有两个主要的初始弱点——较大的束发散角（高达几毫弧度）和百分之几水平的能量 spread。它们降低了束亮度并恶化了基于LPA的光源的相干性。为了实现完全相干辐射，已经提出了几种在LPA束上产生强微聚束的方法。在这些方法中，种子激光用于在电子束中诱导角度调制，并且角度调制通过具有非零纵向位置和横向角度耦合的束线转换为强密度调制。本文提出了一种替代方法，通过使用诱导能量调制的种子激光和将能量调制转换为强密度调制的横向-纵向耦合束线，在LPA束中产生微聚束。与角度调制方法相比，所提出的方法可以使用比其低一个数量级以上的种子激光功率来实现类似的辐射性能。模拟表明，使用所提出的方法，用典型的LPA束可以产生几微焦耳脉冲能量和飞秒持续时间的相干脉冲。
