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Fig. 1. Optical scheme of the diffraction instrument (dimensions not to scale). O, A, A, and P are the source plane, the lens entrance and exit plane, and the detector plane, respectively. The sample is placed at A. Real and demagnified source size are indicated by and . The angular source size and divergence angles before and after the lens are , , and , respectively. 2 is the diffraction angle. The distance of a lens element to the optical axis is x. r, and s are the object and the image distance of the source. (A double crystal monochromator between source and sample for selecting a particular wavelength is not displayed). First citation in article

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Fig. 2. (a) Scanning electron microscope image of the photonic crystal (Ref. 14) used as test sample. The inset shows the geometrical parameters relevant for diffraction. The vectors a and b have a length of 4.2  µm. The outlined zone corresponds to the coherently illuminated sample area defined by the horizontal and vertical coherence lengths _H and _V; (b) x-ray diffraction pattern recorded at an x-ray energy of 28  keV and a detector distance of 1314  mm. Data are presented without any treatment. Intensities are displayed in a logarithmic gray scale to account for large dynamic range. In addition, the scaling is adapted to the higher intensities in the central regions. The first order reflections are strongly dampened by the envelope slit scattering function, which has a minimum close-by. The inset shows the reciprocal lattice vectors for the two principal reflections. First citation in article