Shi Xihang, Kurman Yaniv, Shentcis Michael, Wong Liang Jie, García de Abajo F Javier, Kaminer Ido
Solid State Institute and Faculty of Electrical and Computer Engineering, Technion - Israel Institute of Technology, Haifa, 32000, Israel.
School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore, 639798, Singapore.
Light Sci Appl. 2023 Jun 16;12(1):148. doi: 10.1038/s41377-023-01141-2.
The science and technology of X-ray optics have come far, enabling the focusing of X-rays for applications in high-resolution X-ray spectroscopy, imaging, and irradiation. In spite of this, many forms of tailoring waves that had substantial impact on applications in the optical regime have remained out of reach in the X-ray regime. This disparity fundamentally arises from the tendency of refractive indices of all materials to approach unity at high frequencies, making X-ray-optical components such as lenses and mirrors much harder to create and often less efficient. Here, we propose a new concept for X-ray focusing based on inducing a curved wavefront into the X-ray generation process, resulting in the intrinsic focusing of X-ray waves. This concept can be seen as effectively integrating the optics to be part of the emission mechanism, thus bypassing the efficiency limits imposed by X-ray optical components, enabling the creation of nanobeams with nanoscale focal spot sizes and micrometer-scale focal lengths. Specifically, we implement this concept by designing aperiodic vdW heterostructures that shape X-rays when driven by free electrons. The parameters of the focused hotspot, such as lateral size and focal depth, are tunable as a function of an interlayer spacing chirp and electron energy. Looking forward, ongoing advances in the creation of many-layer vdW heterostructures open unprecedented horizons of focusing and arbitrary shaping of X-ray nanobeams.
X射线光学技术已经取得了长足的进步，能够将X射线聚焦，用于高分辨率X射线光谱学、成像和辐照等应用。尽管如此，许多对光学领域应用产生重大影响的波的调控形式在X射线领域仍然无法实现。这种差异根本上源于所有材料的折射率在高频下趋于1的趋势，使得诸如透镜和镜子等X射线光学元件更难制造，而且效率往往较低。在此，我们提出了一种基于在X射线产生过程中引入弯曲波前从而实现X射线波本征聚焦的X射线聚焦新概念。这一概念可被视为有效地将光学元件整合为发射机制的一部分，从而绕过X射线光学元件所带来的效率限制，能够产生具有纳米级焦斑尺寸和微米级焦距的纳米束。具体而言，我们通过设计非周期性范德华异质结构来实现这一概念，当由自由电子驱动时，该结构能够对X射线进行塑形。聚焦热点的参数，如横向尺寸和焦深，可作为层间距啁啾和电子能量的函数进行调节。展望未来，多层范德华异质结构制造方面的不断进步为X射线纳米束的聚焦和任意塑形开辟了前所未有的前景。
