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X-ray catastrophe focusing from reversed domains in lithium niobate. Top panel is an x-ray topograph of the [00.12] reflection from a reverse-poled thick lithium niobate -axis wafer oriented on a six-circle diffractometer, recorded with an x-ray camera having a pixel size and using a exposure time. One large hexagonal domain covers the right half, with numerous small domains on the left. (Scale bar denotes .) Carbon films were deposited on opposite wafer faces, providing electrically conducting surfaces transparent to the x rays. Succeeding panels were obtained with static applied voltages as labeled, showing a gradual focusing into caustics. Images acquired with an undulator and Si(111) monochromator at Sector 1 of the Advanced Photon Source (Argonne).
Ray-tracing model of x-ray caustic formation. Main panel traces a set of x rays specularly reflected from a sinusoidally modulated surface, with the axis greatly expanded (millimeter units) compared to the axis (meters). Top panel shows the simple diffraction geometry, with undulator radiation well approximated as ideal parallel rays diffracting from a lithium niobate wafer with a controllable applied voltage across its thickness; inset indicates the periodic ferroelectric domain reversal pattern.
Caustic formation from induced domains in unpoled lithium niobate. Top panel is an x-ray topograph of a thick lithium niobate wafer that had not been initially polarized. (Scale bar denotes .) Subsequent panels with 412, 504, and reveal reversible caustic formation associated with induced domains of opposite polarities.
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