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Cartoon of NEXAFS in single shot spectrograph detection at FLASH. Femtosecond x-ray pulses from the SASE undulator disperse on the monochromator grating and pass through the sample. The sample is two-parted for simultaneous measurement of the absorption in the thin-film sample and the unmodified reference spectral distribution for single shot normalization. The transmitted x-rays are converted into visible light on a Ce:YAG crystal and imaged with an ICCD.
Linearization of the detector: The integrated photon energy on the detector for 2000 pulses is shown as a function of the photon energy measured by the gas monitor detector of FLASH. The green dots show the raw detector data whereas the blue curve shows the data after correction for nonlinearities.
(a) Sum over all the pulses of the experiment with the sample in the beam. The La absorption peak is visible at 102.17 eV. (b) and (c) Examples of FLASH pulses with no sample in the beamline. The energy, as well as mode profile, fluctuates on a pulse by pulse basis, requiring the detection of a reference spectrum for each pulse.
The absorption resonance at the edge of the ions in from all accumulated FLASH pulses.
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