High-Transmission Planar X-Ray Waveguides

Abstract

We have studied the propagation of hard x rays in a planar x-ray waveguide with a sub-20 nm guiding layer. To optimize the transmission and to minimize absorption losses, a novel waveguide design based on a two-component cladding was implemented. Optimized transmission is achieved by placing an appropriate interlayer between the cladding and the guiding core. The experimental results along with simulations of field propagation show that high transmission values can be obtained in waveguide optics at parameters relevant for x-ray imaging. These are small beam diameters below 20 nm and the relatively long guiding length necessary for efficient blocking of multi-keV photon energy beams.

Advanced x-ray multilayer waveguide optics

“…For example, the theoretical limits for beam collimation was shown and demonstrated to be in the range of 10 nm depending on the material [26]. With thin film deposition techniques, notably 8 nm [27,28] for the given material could be reached in a planar thin film waveguide with an optimized cladding material (Mo/C /Mo structure embedded in Ge wafers [29]). Furthermore, the single guiding film [30,31] or the cladding film [32,33] can be generalized to a multilayer structure.…”

“…The theoretical limits for beam collimation was shown to be in the range of 10 nm depending on the material [26], and experimental values in the predicted range have been demonstrated, notably 8 nm [27,28] in a planar thin film waveguide with an optimized cladding material (Mo/C /Mo structure embedded in Ge [29]). Several different ways have been used to generate x-ray modes, or more precisely to couple x-ray beams into WGs.…”

“…we can conclude that multi-guide RBCs can result in multiple reflected beams, linked to the incidence angles α i of mode excitation. We use the finite-difference (FD) method to design the waveguides and the corresponding experiments [20,22,25,29,37,38,56,57]. To this end, the precise layer structure is used to simulate the field propagation both inside and outside the waveguide.…”

“…More details on the instrument can be found in [73]. [29]. The beam exiting from the source is filtered by a Si (111) double crystal monochromator (E = 19.9 keV), which is placed in between two conjugate P t mirrors.…”

“…In this diagram, we assume ϕ r is the reflection phase and k z L G H is the phase accumulated during that propagation. Based on Artmann's model [48], ϕ r is given by 29) where k z is the z component of the wave vector, θ i = π/2 − α i , and n 0 is the index of air. Thus the phase shift d ϕ r is given by…”