Center for Advanced Radiation Sources, The University of Chicago, Chicago, IL 60637, USA.
J Synchrotron Radiat. 2011 Jul;18(Pt 4):658-70. doi: 10.1107/S0909049511009423. Epub 2011 May 12.
BioCARS, a NIH-supported national user facility for macromolecular time-resolved X-ray crystallography at the Advanced Photon Source (APS), has recently completed commissioning of an upgraded undulator-based beamline optimized for single-shot laser-pump X-ray-probe measurements with time resolution as short as 100 ps. The source consists of two in-line undulators with periods of 23 and 27 mm that together provide high-flux pink-beam capability at 12 keV as well as first-harmonic coverage from 6.8 to 19 keV. A high-heat-load chopper reduces the average power load on downstream components, thereby preserving the surface figure of a Kirkpatrick-Baez mirror system capable of focusing the X-ray beam to a spot size of 90 µm horizontal by 20 µm vertical. A high-speed chopper isolates single X-ray pulses at 1 kHz in both hybrid and 24-bunch modes of the APS storage ring. In hybrid mode each isolated X-ray pulse delivers up to ~4 × 10(10) photons to the sample, thereby achieving a time-averaged flux approaching that of fourth-generation X-FEL sources. A new high-power picosecond laser system delivers pulses tunable over the wavelength range 450-2000 nm. These pulses are synchronized to the storage-ring RF clock with long-term stability better than 10 ps RMS. Monochromatic experimental capability with Biosafety Level 3 certification has been retained.
BioCARS，一个由美国国立卫生研究院（NIH）支持的、用于在高级光子源（APS）上进行大分子时间分辨 X 射线晶体学的国家用户设施，最近已经完成了升级的基于波动器的光束线的调试，该光束线优化用于单 shot 激光泵浦 X 射线探针测量，时间分辨率最短可达 100 ps。该光源由两个串联的波动器组成，周期分别为 23 和 27 毫米，它们共同提供了在 12 keV 时的高通量粉光能力，以及从 6.8 到 19 keV 的第一谐波覆盖。一个高热负载的斩波器降低了下游组件的平均功率负载，从而保护了能够将 X 射线聚焦到 90 µm 水平和 20 µm 垂直的 Kirkpatrick-Baez 反射镜系统的表面形貌。一个高速斩波器在 APS 储存环的混合模式和 24 束模式下以 1 kHz 的频率隔离单个 X 射线脉冲。在混合模式下，每个隔离的 X 射线脉冲向样品输送多达约 4×10(10)个光子，从而实现了接近第四代 X 射线自由电子激光器（X-FEL）源的时间平均通量。一个新的高功率皮秒激光系统可以提供波长范围为 450-2000nm 的可调谐脉冲。这些脉冲与储存环射频时钟同步，长期稳定性优于 10 ps RMS。保留了具有生物安全级别 3 认证的单色实验能力。
