The advent of accelerator-driven free-electron lasers (FEL) has opened new avenues for high-resolution structure determination via diffraction methods that go far beyond conventional X-ray crystallography methods^{1,2,3,4,5,6,7,8,9,10}. These techniques rely on coherent scattering processes that require the maintenance of first-order coherence of the radiation field throughout the imaging procedure. Here we show that higher-order degrees of coherence, displayed in the intensity correlations of incoherently scattered X-rays from an FEL, can be used to image two-dimensional objects with a spatial resolution close to or even below the Abbe limit. This constitutes a new approach towards structure determination based on incoherent processes^11,12, including fluorescence emission or wavefront distortions, generally considered detrimental for imaging applications. Our method is an extension of the landmark intensity correlation measurements of Hanbury Brown and Twiss¹³ to higher than second order, paving the way towards determination of structure and dynamics of matter in regimes where coherent imaging methods have intrinsic limitations¹⁴.

加速器驱动的自由电子激光器（FEL）的出现为通过衍射方法确定高分辨率结构开辟了新途径，远远超出了常规X射线晶体学方法^{1,2,3,4,5,6,7， 8,9,10}。这些技术依赖于相干散射过程，该过程要求在整个成像过程中保持辐射场的一阶相干性。在这里，我们表明，在来自FEL的非相干散射X射线的强度相关性中显示的高阶相干度可用于对空间分辨率接近甚至低于阿贝极限的二维物体成像。这构成了基于不连贯过程的结构确定的新方法^11,12包括荧光发射或波前畸变，通常被认为对成像应用有害。我们的方法是汉伯里Brown和特威斯的界标强度相关测量的延伸¹³以比第二阶数越高，铺路朝向判定结构和物质的动力学机制，其中相干成像方法具有固有的限制的方式¹⁴。