Lengeler B
II. Physikalisches Institut B, RWTH Aachen, 52056 Aachen, Germany.
Naturwissenschaften. 2001 Jun;88(6):249-60. doi: 10.1007/s001140100221.
Highly brilliant synchrotron radiation sources have opened up the possibility of using coherent X-rays in spectroscopy and imaging. Coherent X-rays are characterized by a large lateral coherence length. Speckle spectroscopy is extended to hard X-rays, improving the resolution to the nm range. It has become possible to image opaque objects in phase contrast with a sensitivity far superior to imaging in absorption contrast. All the currently available X-ray sources are chaotic sources. Their characterization in terms of coherence functions of the first and second order is introduced. The concept of coherence volume, defined in quantum optics terms, is generalized for scattering experiments. When the illuminated sample volume is smaller than the coherence volume, the individuality of the defect arrangement in a sample shows up as speckle in the scattered intensity. Otherwise, a configurational average washes out the speckle and only diffuse scattering and possibly Bragg reflections will survive. The loss of interference due to the finite detection time, to the finite detector pixel size and to uncontrolled degrees of freedom in the sample is discussed at length. A comparison between X-ray scattering, neutron scattering and mesoscopic electron transport is given. A few examples illustrate the possibilities of coherent X-rays for imaging and intensity correlation spectroscopy.
高亮度同步辐射源开启了在光谱学和成像中使用相干X射线的可能性。相干X射线的特点是具有较大的横向相干长度。散斑光谱学已扩展到硬X射线，将分辨率提高到了纳米范围。已能够以相位对比的方式对不透明物体进行成像，其灵敏度远高于吸收对比成像。目前所有可用的X射线源都是混沌源。介绍了根据一阶和二阶相干函数对它们进行的表征。用量子光学术语定义的相干体积概念被推广到散射实验中。当被照射的样品体积小于相干体积时，样品中缺陷排列的个体性会在散射强度中表现为散斑。否则，构型平均会消除散斑，只有漫散射以及可能的布拉格反射会留存下来。详细讨论了由于有限的检测时间、有限的探测器像素尺寸以及样品中不受控制的自由度导致的干涉损失。对X射线散射、中子散射和介观电子输运进行了比较。几个例子说明了相干X射线在成像和强度相关光谱学方面的可能性。
