Diffraction gratings with two-orders-of-magnitude-enhanced dispersion rates for sub-meV resolution soft X-ray spectroscopy

Shvyd'ko, Yu.

doi:10.1107/S1600577520008292

Figure 2
Reflectivity and angular dispersion $[{{\cal D}}]$ of soft-X-ray diffraction gratings similar to those in Fig. 1

, but calculated in non-coplanar asymmetric scattering geometry as presented in panels (a) and (a′). In the non-coplanar case, the scattering plane ( $[{\bf{K}}_{0},{\bf{K}}_{\rm{H}}]$ ) and the dispersion plane ( $[{\bf{H}},\hat{{\bf{z}}}]$ ) are no longer parallel. They are perpendicular in the case presented here. The Bragg reflectivity dependences shown in rows (b)–(d) are calculated for different asymmetry angles η. In each (b), (c) or (d) case, the azimuthal angle of incidence $[\phi]$ = $[\phi_{0}]$ [see Shvyd'ko (2004

) for the definition] is chosen such that $[\Phi_{0}]$ = $[\Phi^{\,{\prime}}_{0}]$ , where $[\Phi_{0}]$ and $[\Phi^{\,{\prime}}_{0}]$ are the angles between the crystal surface and K₀ and K_H, respectively, as measured at the peak reflectivity. The Bragg reflectivities at fixed photon energy E = E₀ = 930 eV and $[\phi]$ = $[\phi_{0}]$ as a function of θ and Φ are shown in (b₁)–(d₁) and (b₂)–(d₂), respectively. Bragg reflectivities calculated as a function of E with θ fixed at the peak reflectivity values are presented in (b₃), (c₃), and (d₃), while graphs in (b₄), (c₄), and (d₄) show the reflectivity mapped on Φ′ that changes simultaneously with E due to angular dispersion. Largest $[{{\cal D}}]$ is at smallest $[\Phi_{0}]$ and $[\Phi^{\,{\prime}}_{0}]$ .

JOURNAL OF
SYNCHROTRON
RADIATION

ISSN: 1600-5775

Volume 27| Part 5| September 2020| Pages 1227-1234

https://doi.org/10.1107/S1600577520008292

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