Jark Werner, Pérennès Fréderic, Matteucci Marco
Sincrotrone Trieste ScpA, SS 14 km 163.5, 34012 Basovizza (TS), Italy.
J Synchrotron Radiat. 2006 May;13(Pt 3):239-52. doi: 10.1107/S0909049506004936. Epub 2006 Apr 13.
Like visible light, X-rays can also be focused by refraction in transmission lenses. For visible light this requires convex lenses while for X-rays one needs to use concave lenses instead. Both lens types can be lightened by the material removal strategy introduced by Fresnel, which results in a lens subdivided into zones. Until now, for the focusing of X-rays, stacks of standard lenses and of Fresnel lenses have mostly been produced. The first are dubbed compound refractive lenses, abbreviated as CRL. State-of-the-art systems of this kind now achieve almost theoretical performance for the focus size and the transmission. On the other hand, the latter Fresnel systems, which promise to provide larger apertures, are still in their infancy. This report discusses systematically the properties of two possible schemes for their realisation. It then compares the optimized apertures of these two schemes with those for CRLs. The best Fresnel lenses in this study are found to provide experimentally more than 50% of the expected refraction efficiency at 8.5 keV photon energy. The photon flux in their focus is then almost identical to that of perfect Be CRLs with the same focal length. This report will also interpret experimental data reported previously for other Fresnel lenses.
与可见光一样，X射线也可以通过透射透镜中的折射来聚焦。对于可见光，这需要凸透镜，而对于X射线，则需要使用凹透镜。这两种透镜都可以通过菲涅耳引入的材料去除策略减轻重量，从而形成一个划分为多个区域的透镜。到目前为止，为了聚焦X射线，大多生产标准透镜和菲涅耳透镜的堆叠。前者被称为复合折射透镜，简称为CRL。目前这种最先进的系统在焦点尺寸和透射率方面几乎达到了理论性能。另一方面，后者的菲涅耳系统有望提供更大的孔径，但仍处于起步阶段。本报告系统地讨论了实现这两种方案的特性。然后将这两种方案的优化孔径与CRL的孔径进行比较。在本研究中，发现最佳的菲涅耳透镜在8.5 keV光子能量下实验上可提供超过预期折射效率的50%。然后，它们焦点处的光子通量几乎与具有相同焦距的完美铍CRL的光子通量相同。本报告还将解释先前报道的其他菲涅耳透镜的实验数据。
