Electron and X-ray beams originating from compact laser-wakefield accelerators have very small source sizes that are typically on the micrometre scale. Therefore, the beam divergences are relatively high, which makes it difficult to preserve their high quality during transport to applications. To improve on this, tremendous efforts have been invested in controlling the divergence of the electron beams, but no mechanism for generating collimated X-ray beams has yet been demonstrated experimentally. Here we propose and realize a scheme where electron bunches undergoing focusing in a dense, passive plasma lens can emit X-ray pulses with divergences approaching the incoherent limit. Compared with conventional betatron emission, the divergence of this so-called plasma lens radiation is reduced by more than an order of magnitude in solid angle, while maintaining a similar number of emitted photons per electron. This X-ray source offers the possibility of producing brilliant and collimated few-femtosecond X-ray pulses for ultra-fast science, in particular for studies based on X-ray diffraction and absorption spectroscopy.

源自紧凑型激光尾场加速器的电子和 X 射线束具有非常小的源尺寸，通常为微米级。因此，光束发散度相对较高，这使得在运输到应用过程中难以保持其高质量。为了改进这一点，人们在控制电子束的发散方面投入了巨大的努力，但尚未通过实验证明产生准直 X 射线束的机制。在这里，我们提出并实现了一种方案，其中在密集的无源等离子体透镜中进行聚焦的电子束可以发射散度接近非相干极限的 X 射线脉冲。与传统的电子感应加速器发射相比，这种所谓的等离子体透镜辐射的发散在立体角上减少了一个数量级以上，同时保持每个电子发射的光子数量相似。这种 X 射线源为超快科学，特别是基于 X 射线衍射和吸收光谱的研究提供了产生明亮且准直的几飞秒 X 射线脉冲的可能性。