Development of sub-nano second time-resolved XAFS technoque

本研究的目的是建立时间分辨率为亚纳秒级的时间分辨XAFS技术，以便对溶液和表面化学反应过程中产生的短寿命金属进行结构和电子态分析。由于色散XAFS （DXAFS）仪器是不可逆反应系统的一种独特技术，我们开发了一种快速CCD系统来实现目标时间分辨率。首先对同步加速器x射线脉冲与同步加速器环主时钟之间的时间抖动进行了评估，并明确了13.3ps的抖动足以满足我们的时间分辨率。采用ATMEL公司的TH7888A芯片开发了快速CCD系统。在该系统中，CCD用作线性检测器（一行）和存储区（约1000行）。当用同步加速器环主时钟（794 kHz）驱动CCD芯片中的线路传输时，探测器线路上产生的电荷仅供一个x射线脉冲使用。由于电荷通过CCD芯片的线传输移动到存储区域，存储在存储区域上的电荷响应于时间分辨的x射线强度。由于PF-AR的NW2A光束线处的x射线强度太强，无法将x射线直接照射到CCD芯片上，因此使用荧光粉（P46）将x射线转换为可见光，并使用与CCD芯片光学耦合的锥形光纤板将可见光传输到探测器线，从而降低了可见光的图像。采用高功率Nd: YAG脉冲激光系统（Powerlite 8000）产生了短寿命的光激发金属。研制了泵浦Nd: YAG激光器与探测x射线脉冲之间的定时系统，实现了亚纳秒时间分辨的DXAFS快速CCD测量系统。通过对标准样品的测量，对新研制的亚纳秒时间分辨快速CCD DXAFS系统在一定x射线能量下的性能进行了评价。在XANES光谱中观察到清晰的特征，表明所开发的CCD系统可以很好地作为DXAFS仪器的线性检测器。仅用一个x射线脉冲测量的XAFS光谱与用常规步进扫描技术测量的光谱几乎一致。当连续x射线脉冲的时间间隔为1.26 μs时，时间过程测量成为可能。我们已经成功地开发了世界上最快的DXAFS仪器。少

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