Micro-XAS Using Tapered Capillary Concentrating Optics

Tapered capillary optics are a promising choice for producing micro-beams at third generation sources. The reproducible energy dependence of their X-ray transmission, and fixed output beam position make them well suited for micro-XAS applications. Fiber optics techniques have been developed to produce long (1 m) capillaries which provide a good match to the low divergence undulator beams at third generation sources. The results of X-ray tests made at the NSLS indicate the performance of many of the capillaries closely match theoretical values. Currently these provide a monochromatic beam of about 10⁶ ph/sec/μm² at an unfocused bending magnet beamline. High quality X-ray images and micro-XAFS have been obtained at the NSLS with better than 3 μm resolution. The same capillaries should provide more than 10¹⁰ ph/sec/μm² at an APS undulator, indicating that sub-μm XAS is possible.