Abstract
This work presents the improvements in the design and testing of polarimeters based on channel-cut crystals for nuclear resonant scattering experiments at the 14.4 keV resonance of 57Fe. By using four asymmetric reflections at asymmetry angles of α1 = -28°, α2 = 28°, α3 = -28° and α4 = 28°, the degree of polarization purity could be improved to 2.2 × 10-9. For users, an advanced polarimeter without beam offset is now available at beamline P01 of the storage ring PETRAIII.
Highlights
Nuclear resonant scattering of synchrotron radiation (NRS) is an established methodology ranging from the study of structure and dynamics of condensed matter (Gerdau & de Waard, 1999, 2000; Rohlsberger, 2004) to the realization of quantum optical phenomena (Siddons et al, 1995; Toellner et al, 1995; Rohlsberger et al, 2010, 2012; Schulze, 2018)
We have developed a polarimeter for the 14.4 keV nuclear resonance energy of 57Fe that uses four asymmetric reflections each for the polarizer and analyzer
We improved the degree of polarization purity by more than one order of magnitude compared with previously published performances of polarimeters working at this energy
Summary
Nuclear resonant scattering of synchrotron radiation (NRS) is an established methodology ranging from the study of structure and dynamics of condensed matter (Gerdau & de Waard, 1999, 2000; Rohlsberger, 2004) to the realization of quantum optical phenomena (Siddons et al, 1995; Toellner et al, 1995; Rohlsberger et al, 2010, 2012; Schulze, 2018). Nuclear resonances have a very narrow energy bandwidth of typically 10À7 to 10À11 eV, in the case of 57Fe the natural linewidth is 4.7 neV The challenge of this method is to discriminate the small fraction of nuclear resonant scattered photons against the energetically broad synchrotron beam. The last one is a technique that makes use of the strong optical activity that is inherent to the nuclear scattering process In this technique an X-ray polarimeter is used to filter the resonantly scattered photons that have undergone a change in their polarization state with respect to the white beam, if the nuclei are exposed to a magnetic field (see Fig. 1). For the equipment of a nuclear resonance beamline with a zero beam-offset polarimeter, we have improved these values by using four reflection channel-cut crystals with smaller asymmetry angles. The corresponding design and its performance are discussed in this article
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