Towards perfectly linearly polarized x-rays

Scanning high-sensitive x-ray polarization microscopy

“…For the first time, it has been possible to focus and recollimate x-rays without changing the polarization (within the limits of measurement accuracy). Second, a degree of polarization purity has been measured that is half an order of magnitude better than previously achieved purities (δ 0 = 8 × 10 −11 at 6.456 keV [32]), at twice the photon energy.…”

“…The development of x-ray polarimetry has considerably progressed during the last ten years [6][7][8]. Driven by the quest for the first observation of vacuum birefringence [9], x-ray quantum optics exploiting nuclear resonant scattering [10][11][12], and x-ray polarization-sensitive spectroscopy [4,13], the degree of polarization purity has been improved to the level of 5.5 × 10 −11 [14]. High precision x-ray polarimeters are based on multiple reflections in channel-cut crystals at Bragg angles close to 45 • [15].…”

X-ray polarimetry and its application to strong-field quantum electrodynamics

“…Tischler and Batterman [ 63 ] provided that the resulting contribution of all reflections is dependent on the amplitude for each detour: Based on Equation (8), they calculated the -beam integrated intensities for the (622) reflection of germanium (Ge) and silicon (Si). The ratio of intensities is very close to the ratio of atomic numbers to the fourth power [ 51 , 55 , 58 , 59 ] :

Figure 6 Schematic of a channel-cut polarizer with reflections. Thin lines indicate the lattice planes for the 45° Bragg reflection, which are parallel to the surface in this case.

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“…In 2022, Schulze et al . [ 59 ] reported an unprecedented purity of linear polarization of X-rays at the High Energy Density (HED) instrument of the European XFEL of , provided by silicon channel cuts. They calculated the theoretical limitation of polarization purity as by Equation (7) with the horizontal divergence of 0.27 μrad and a negligible vertical divergence.…”

“…However, they used more realistic laser and XFEL parameters, for example, the accelerator setpoint and bunch charge dependency on the number of probe photons, yielding . This number is valid for the SASE mode of the European XFEL; the spectral matching aspect was published later [ 59 ] , which effectively reduces the available number of photons. They also discussed XFEL pulse lengthening for channel-cut polarizers (cf.…”