By illuminating matter with bright and intense light, researchers gain insights into material composition and properties. In the regime of extremely short wavelengths, X-ray free-electron lasers (XFELs) with exceptional peak brilliance have unveiled crucial details about the structures, dynamics and physics of various materials. Although X-ray focusing optics to enhance the intensity have progressed, achieving a single-nanometre focal spot that fully exploits the source performance remains elusive. Aberrations arising from reflective optical schemes noticeably degrade the focal spot, even in the presence of inevitably slight angular transition and pointing errors. Here we present an approach that directly forms a source image in an extremely small focal spot, achieving 7 nm focusing, in both transverse dimensions, of 9.1 keV XFELs with the extremely high intensity of 1.45 × 10²² W cm⁻². This was made possible by a scheme combining concave and convex X-ray mirrors with suppressed aberrations and high angular tolerances. The attained highly intense X-rays, surpassing the previous intensity by a hundred-fold, induced the vigorous ionization of chromium, suggesting the creation of solid-density heavy bare atomic nuclei. Our results, which demonstrate the realization of stable ultraintense XFEL beams by forming demagnified source images, hold immediate significance to a wide range of research fields, including atomic, molecular and optical physics and high-energy-density sciences.

通过用明亮和强光照射物质，研究人员可以深入了解材料的成分和特性。在极短波长范围内，具有卓越峰值亮度的 X 射线自由电子激光器 (XFEL) 揭示了有关各种材料的结构、动力学和物理的重要细节。尽管用于增强强度的 X 射线聚焦光学器件已经取得了进展，但实现充分利用源性能的单纳米焦点仍然难以实现。即使存在不可避免的轻微角度过渡和指向误差，反射光学方案产生的像差也会显着降低焦点。在这里，我们提出了一种直接在极小的焦斑中形成源图像的方法，在两个横向维度上实现 9.1 keV XFEL 的 7 nm 聚焦，强度高达 1.45 × 10 ²²  W cm ^{- 2}。这是通过将凹面和凸面 X 射线镜与抑制像差和高角度公差相结合的方案实现的。所获得的高强度 X 射线比之前的强度高出一百倍，引发了铬的剧烈电离，这表明固体密度重裸原子核的产生。我们的研究结果证明了通过形成缩小的源图像实现了稳定的超强 XFEL 光束，这对原子、分子和光学物理以及高能量密度科学等广泛的研究领域具有直接意义。