Reconstruction of the near-field distribution in an X-ray waveguide array

Zhong, Q.; Melchior, L.; Peng, J.; Huang, Q.; Wang, Z.; Salditt, T.

doi:10.1107/S1600576717004630

Figure 1
(a) Schematic of the experimental setup. The X-ray waveguide array (WGA) is positioned at f, which is the distance from the exit of the Kirkpatrick–Baez (KB) device to the sample. The incoming beam with photon energy E and primary intensity I₀ is coupled into the Ni/C WGA with working length L, which tailors the near field to the desired shape. The far-field intensity distribution is recorded at a distance of D behind the WGA exit by a two-dimensional pixel detector. (b) A schematic of the structure of the WGA, consisting of seven guiding layers in red (d_i, $[i = 1,\ldots, 7]$ ) and eight cladding layers in purple (c_j, $[j = 1,\ldots, 8]$ ). After the pre-focus beam has been coupled, the guided mode is produced in the different guiding layers. With the working length L, the exit phase $[\varphi _{i}]$ from the corresponding guiding layers i can be controlled by the variation of the layer thickness d_i. The parameters at the exit of the WGA can be optimized such that the lines of the exit phase $[\varphi _{i}]$ describe a circle with radius R, resulting in constructive interference in a quasi-focal spot (F) outside the WGA. The phase of the reference sample with length L is $[\varphi _{0}]$ , with the corresponding guiding layer d₀ and cladding layers c₀. (c) Sketch of a slab waveguide with two cladding layers c_j and c_j+1. Under the influence of the electric field inside the waveguide [ $[\psi(z,x) = \psi(x)\exp(i\beta z)]$ ], the symmetrical guided modes ( $[\psi _{{0}},\psi _{{2}}]$ ) and the asymmetrical mode $[\psi _{{1}}]$ propagate inside the guiding layer depending on the different layer thickness d_i.

JOURNAL OF
APPLIED
CRYSTALLOGRAPHY

ISSN: 1600-5767

Volume 50| Part 3| June 2017| Pages 701-711

https://doi.org/10.1107/S1600576717004630

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