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WEPP34 |
Towards Single Shot X-ray Absorption Spectroscopy Using the Broadband Emission at the SwissFEL Aramis Undulator | |
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| X-ray absorption spectroscopy (XAS) is a powerful tool for the investigation of the electronic and structural environment of the absorbing atom. The high element specificity of XAS is gained by photon energies around resonant absorption edges of the probed material. Dynamics on a femtosecond timescale can be accessed with time resolved XAS (TR-XAS) using a laser to photo-excite the sample and intense femtosecond X-ray pulses from a free-electron laser to probe with XAS. A primary drawback to the implementation of TR-XAS at X-ray free-electron lasers is the general requirement to scan the photon energy for obtaining the spectrum. Moreover, fluctuations of the X-ray spectrum and intensity due to the self-amplified stimulated emission lead to normalization problems. To tackle these issues we propose a novel scheme for TR-XAS using a broadband emission mode of the Aramis undulator at SwissFEL providing dE/E = 2% bandwidth, which is sufficient to cover a XAS spectrum. By utilizing a transmission grating, the chirped beam is split into 1st, 0th and -1st orders having similar intensity. By placing a sample in the 1st or -1st diffraction order we can record sample and reference signal in order to normalize intrinsic spectral and intensity fluctuations on a shot-to-shot basis. The beams are sent onto a single shot spectrometer that uses the <111> reflection from a strongly bent thin Si crystal, in order to characterize the broadband, chirped emission of every free-electron laser shot. In this contribution, we present a quantitative data analysis and compare the shot-to-shot normalization method with the conventional data analysis without beam splitting, showing a significant improvement of the data quality in the first case. We show XAS measurements at the Nickel K-edge on thin foils and Nickelsulfamate solutions. The presented experiments form the basis for future time-resolved research comprising more advanced diffractive x-ray optics, as well as pump-probe schemes. | ||
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