This paper accounts for selected detector developments carried out over the past 15 years within the ESRF X-ray Absorption Spectroscopy group. This includes various types of photodiodes used as integrated current detectors. Special emphasis is put on the long-standing development of a Si drift-diode array suitable for energy-dispersive detection of X-ray fluorescence. This detector, which is now operational, was used to record high-quality XMCD/XAFS spectra on [Fe70Pt30] nanoparticles highly dispersed on a Si wafer. Using numerically deconvoluted spectra, energy resolution was decreased to 82 eV for the Si Kalphabeta line, 126 eV for the Fe Kalpha line and 176 eV for the Pt Lalpha line. A high-vacuum-compatible high-energy-resolution crystal analyzer was also installed on ID12, making it possible to record X-ray fluorescence excitation spectra in the photon-in/photon-out mode over a wide spectral range. Prospects of adapting these methods in order to investigate biological samples are briefly discussed.
A quarter-wave plate made of a ca 16 mum-thick silicon single-crystal was used at energies as low as 2.8 keV to convert circularly polarized photons into linearly polarized photons. Coupled to a linear polarimeter, this quarter-wave plate enabled the characterization of the circular polarization rate of the radiation emitted by one of the ESRF helical undulators, Helios-I. The measured value (ca 97%) is in good agreement with theoretical predictions. Special attention was paid to the alignment procedures of all relevant optical components of the beamline.
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