Two-Dimensional Hard X-Ray Beam Compression by Combined Focusing and Waveguide Optics

A two-dimensionally confining x-ray channel waveguide structure is combined with a high gain Kirkpatrick-Baez prefocusing mirror system yielding a hard x-ray beam with a cross section of $25\times 47{\mathrm{n}\mathrm{m}}^2$ (FWHM). Unlike the previously employed resonant beam coupling scheme, the incoming beam is coupled in from the front side of the waveguide and the waveguided beam is no longer accompanied by spurious reflected or transmitted beams. The field distribution in the waveguide channel has been calculated numerically. The calculated transmission and far-field intensity pattern are in good agreement with the experimental results.

Figure 1

(a) The lithographic structure consisting of planar waveguides (left), a grating (middle), and several separated 2D waveguides. (c) The angularly aligned structure is translated through the focus of the Kirkpatrick-Baez mirror system to locate the positions of the individual waveguide channels. (b) Scanning electron microscopy micrograph showing the front side of a 2D XWG.

Figure 2

Schematic of the experimental setup: the 2D-XWG structure is aligned in the focus of a Kirkpatrick-Baez mirror system. The focused beam is coupled into the front side of the waveguide and propagates in the WG core, as illustrated by the numerical simulation of the device: The intensity of the electric field in the 2D XWG is shown in logarithmic color scales. The overilluminating parts of the beam are damped in the absorbing cladding. Only the waveguided beam, without side peaks, spurious reflected, or primary beams, is extracted at the exit of the structure.

Figure 3

CCD images of the beam defined (a) by only the Kirkpatrick-Baez focusing optics and (b) by the combined focusing and waveguiding optics, both taken 170 mm behind the focal spot of the KB optics illustrating the filtering properties of the 2D waveguide structure.

Figure 4

Measured far-field pattern of the waveguided beam in the vertical (solid squares) and the horizontal (open stars) direction, both in linear (left) and logarithmic (right) scales. The lines show the simulated far field of a 2D XWG with a PMMA guiding layer of $30\times 70{\mathrm{n}\mathrm{m}}^2$ (solid line: vertical; dashed line: horizontal). These values correspond to a beam size of $25\times 47{\mathrm{n}\mathrm{m}}^2$ (FWHM) in the near field and directly behind the 2D-XWG structure.