Quantitative investigation of linear arbitrary polarization in an APPLE-II undulator

Abstract

Insertion devices are utilized at synchrotron radiation facilities around the world for their capability to provide a high-brilliance X-ray beam. APPLE-II type undulators are especially important for their capacity to switch between a variety of photon beam polarization states. A high-precision soft X-ray polarimeter has been used to investigate the polarization calibration of an APPLE-II undulator (period length u = 64 mm) installed on beamline I06 at Diamond Light Source. Systematic measurement of the beam polarization state at a range of linear arbitrary angles has been compared with the expected result for a given set of undulator gap and row phase parameters calculated from theory. Determination of the corresponding Stokes-Poincaré parameters from the measured data reveals a discrepancy between the two. The limited number of energy/polarization combinations included in the undulator calibration tables necessitates the use of interpolated values for the missing points which is expected to contribute to the discrepancy. However, by modifying the orbit of the electron beam through the undulator by at least 160 mm it has been found that for certain linear polarizations the discrepancies can be corrected. Overall, it is suggested that complete correction of the Stokes-Poincaré parameters for all linear angles would require alteration of both these aspects.

Probing photoinduced rearrangements in the NdNiO3 magnetic spiral with polarization-sensitive ultrafast resonant soft x-ray scattering

“…The x-ray pulses were produced using the hybrid filling mode of the storage ring, consisting of a contiguous train of electron bunches followed by a single bunch with a higher charge of 3 nC, which was separated by 250 ns from the bunch train. A pair of APPLE-II undulators were then used to generate soft x-ray pulses of ∼80 ps duration with control over the linear polarization direction [35]. A grating monochromator then selected an x-ray photon energy of 852 eV with 0.1 eV bandwidth, which is resonant with the nickel L 3 edge.…”