期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2014
卷号：111
期号：16
页码：5825-5830
DOI：10.1073/pnas.1404336111
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：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 x 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.
