Development of sub-nano second time-resolved XAFS technoque

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The purpose of this research is to establish the time-resolved XAFS technique with the time resolution ofthe order of sub-nano second in order to perform the structure and electronic-state analyses of the short-lived metal species generated in the course of chemical reactions in solutions and on surfaces. Because the dispersive XAFS (DXAFS) instrument is a unique technique for in-eversible reaction systems, we have developed a fast CCD system to achieve the target time resolution. The timing jitter between the synchrotron X-ray pulse and the master clock of synchrotron ring has been first evaluated and clarified that the jitter of 13.3ps is enough for our time resolution. The fast CCD system has been developed using the TH7888A chip (ATMEL). In this system, the CCD is used as a linear detector (one line) and a memory area (ca. 1000 lines). When the line transfer in the CCD chip is driven with the master clock of synchrotron ring (794 kHz), the generated charges on a detector line is ca … More used by only one X-ray pulse. Because the charges are moved to the memory area by the line transfer of the CCD chip, the stored charges on the memory area conespond to the time-resolved X-ray intensities.The X-ray intensity at the NW2A beam line of PF-AR is too strong to inadiate X-ray directly to the CCD chip, and thus the phosphor (P46) is used to convert the X-ray to visible light and the image of the visible light is reduced using a tapered-fiber plate which is optically coupled with the CCD chip to transfer the visible light to the detector line. A slit system has also been developed to prevent the irradiation of X-ray into the memory area The high power Nd: YAG pulsed laser system (Powerlite 8000) has been introduced to generate the short-lived photo-excited metal species. The timing system between the pump Nd: YAG laser and the probe X-ray pulse has been developed and achieved the sub-nano second time-resolved DXAFS measurement system with the fast CCD.The performance of a newly developed sub-nano second time-resolved DXAFS system with fast CCD has been evaluated at some X-ray energies by measuring the standard samples. The clear characteristics are observed in the XANES spectra, indicating that the developed CCD system woks well as the linear detector for the DXAFS instrument. The XAFS spectra measured with only one X-ray pulse are almost in agreement with that measured using the conventional step-scanning technique. The time course measurements become possible with the time interval (1.26 μs) of succeeding X-ray pulses. We have succeeded in developing the fastest DXAFS instrument in the world. Less