DESY, Notkestrasse 85, 22607 Hamburg, Germany.
IUCrJ. 2015 Feb 3;2(Pt 2):230-45. doi: 10.1107/S2052252514024269. eCollection 2015 Mar 1.
Structural studies in general, and crystallography in particular, have benefited and still do benefit dramatically from the use of synchrotron radiation. Low-emittance storage rings of the third generation provide focused beams down to the micrometre range that are sufficiently intense for the investigation of weakly scattering crystals down to the size of several micrometres. Even though the coherent fraction of these sources is below 1%, a number of new imaging techniques have been developed to exploit the partially coherent radiation. However, many techniques in nanoscience are limited by this rather small coherent fraction. On the one hand, this restriction limits the ability to study the structure and dynamics of non-crystalline materials by methods that depend on the coherence properties of the beam, like coherent diffractive imaging and X-ray correlation spectroscopy. On the other hand, the flux in an ultra-small diffraction-limited focus is limited as well for the same reason. Meanwhile, new storage rings with more advanced lattice designs are under construction or under consideration, which will have significantly smaller emittances. These sources are targeted towards the diffraction limit in the X-ray regime and will provide roughly one to two orders of magnitude higher spectral brightness and coherence. They will be especially suited to experiments exploiting the coherence properties of the beams and to ultra-small focal spot sizes in the regime of several nanometres. Although the length of individual X-ray pulses at a storage-ring source is of the order of 100 ps, which is sufficiently short to track structural changes of larger groups, faster processes as they occur during vision or photosynthesis, for example, are not accessible in all details under these conditions. Linear accelerator (linac) driven free-electron laser (FEL) sources with extremely short and intense pulses of very high coherence circumvent some of the limitations of present-day storage-ring sources. It has been demonstrated that their individual pulses are short enough to outrun radiation damage for single-pulse exposures. These ultra-short pulses also enable time-resolved studies 1000 times faster than at standard storage-ring sources. Developments are ongoing at various places for a totally new type of X-ray source combining a linac with a storage ring. These energy-recovery linacs promise to provide pulses almost as short as a FEL, with brilliances and multi-user capabilities comparable with a diffraction-limited storage ring. Altogether, these new X-ray source developments will provide smaller and more intense X-ray beams with a considerably higher coherent fraction, enabling a broad spectrum of new techniques for studying the structure of crystalline and non-crystalline states of matter at atomic length scales. In addition, the short X-ray pulses of FELs will enable the study of fast atomic dynamics and non-equilibrium states of matter.
结构研究，特别是晶体学，已经并且仍然受益于同步辐射的应用。第三代低发射度储存环提供了聚焦光束，达到了微米级，足以用于研究尺寸小至数微米的弱散射晶体。尽管这些光源的相干分数低于 1%，但已经开发了许多新的成象技术来利用部分相干辐射。然而，纳米科学中的许多技术都受到这个相当小的相干分数的限制。一方面，这种限制限制了通过依赖光束相干性质的方法研究非晶材料的结构和动力学的能力，如相干衍射成象和 X 射线相关光谱学。另一方面，由于同样的原因，在超小衍射极限焦点中的通量也受到限制。与此同时，具有更先进的格子设计的新型储存环正在建设或考虑之中，这些储存环的发射度将显著减小。这些光源的目标是在 X 射线区域达到衍射极限，并将提供大约一个到两个数量级更高的光谱亮度和相干性。它们特别适合于利用光束相干性质的实验，以及在数纳米的几个纳焦点尺寸的实验。尽管单个储存环源的 X 射线脉冲长度约为 100 ps，但足以跟踪较大的结构变化，但在这些条件下，无法详细地记录如视觉或光合作用等更快的过程。具有非常短而强的高相干性的线性加速器（linac）驱动的自由电子激光（FEL）光源，规避了一些当前储存环光源的限制。已经证明，它们的单个脉冲短到足以在单脉冲曝光时避免辐射损伤。这些超短脉冲还使时间分辨研究速度比标准储存环源快 1000 倍。在不同的地方，正在为一种新型的 X 射线源进行开发，该源将 linac 与储存环结合在一起。这些能量回收直线加速器有望提供几乎与 FEL 一样短的脉冲，具有与衍射极限储存环相当的亮度和多用户能力。总之，这些新型 X 射线源的发展将提供更小、更强大的 X 射线束，具有更高的相干分数，使研究物质的结晶和非晶态结构的广泛新技术成为可能，达到原子尺度。此外，FEL 的短 X 射线脉冲将能够研究快速原子动力学和非平衡态物质。
