Beamline commissioning

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10.05.2012 The first highest quality spectra!

The figures below show two copper foil spectra in comparison with two ones taken at Hasylab. In both cases each spectrum took about 20 min. All 4 spectra practically fully merge (!) except in the XANES where our better energy resolution gives sharper features.

 

 EXAFS with different k-weighting:

 

22.12.2011 The first absorption spectra measured at the sample position

The figures below show the first spectra of copper foil measured in transmission mode using two ionization chambers. The chambers were open to atmosphere and therefore the signals were not optimal. If filled with Ar, the second chamber is expected to give ~30 times higher signal. The hardware gating system is not functional yet; the synchronization is done by software means. This is an additional source of noise at present. The XANES spectra are with constant dE steps of 0.5 eV and acquisition time 0.1 s per point. The EXAFS spectra are with constant dk steps of 0.025 Å^-1 and acquisition time increasing as k². The comparison is made with the spectra measured at Hasylab/E4 beamline in transmission mode. One can see a better energy resolution at CLÆSS (better resolved features at the absorption edge) due to the beam collimation in front of the monochromator.

Yet better energy resolution can be obtained with the Si 311 crystal pair, at the expense of photon flux:

The EXAFS spectra measured with the Si311 crystals are noisier, have several uncompensated glitches and therefore are not demonstrated here. This operation mode will be improved by fine adjustment of the beamline optics and by the ongoing development of the timing system.

28.10.2011 The first absorption spectra measured in optical hutch

The figures below show the first spectra of copper foil at the Cu K-edge measured in fluorescence mode by the 4-diode beam position monitor (BPM). The XANES spectra are with constant dE steps of 0.5 eV and acquisition time 0.25 s per point. The EXAFS spectra are with constant dk steps of 0.025 Å^-1 and acquisition time proportional to k² (0.1 to 0.7 s per point, ~12 min in total). The comparison is made with the spectra measured at Hasylab/E4 beamline in transmission mode. The washed-out absorption features are due to the self absorption effect which cannot be corrected here because the fluorescence is not normalized to the incident intensity (the BPM itself is an I0 monitor and there is none other upstream of it). The increasing trend is due to decreasing absorption in the used 1-mm-thick carbon filter.