Future Prospects of XAFS Researches Using High Brilliance Photon Sources

Abstract

Future prospects in XAFS researches to be developed by high brilliance photon sources are discussed. Above a dilute limit, sensitivity and time resolution are enhanced with the increase in brilliance, detector effeciency and focusing capability. It is shown that a multipole wiggler and multi-element solid state detector improve both sensitivity and time resolution by an order of magnitude. Applications to structural studies of dilute systems, in particular, surface and interfaces are presented. A “tunable” X-ray undulator inserted in an ultra-low (<10 nrad) emittance storage ring, which covers a hard X-ray (4-30 keV) region using the fundamental and third higher harmonic radiations, further improves the present limitations on sensitivity and resolutions in time, space and energy. Feasibility of a variable gap/bandpath undulator combined with new quick scanning techniques for applications in time-resolved studies is discussed. By optimizing an undulator band width for a scan, without varying undulator gap, XAFS is obtained by simple scanning of monochromator (Q-scan I). A new quick scanning technique for time-resolved studies on dilute systems based on an energy dispersive geometry (Q-scan II) is proposed. Design considerations of a “tunable” X-ray undulator XAFS beamline at SPring-8 are presented, in which either a high flux or a microfocus high energy resolution beam is obtained by a fixed-exit double-axis (2+2) crystal monochromator followed by crossed eliptical mirrors. A concept of “ring” detector for microfucusing in a fluorescence detection mode is also proposed.