Natural focusing of x rays from ferroelectric lithium niobate wafers

The interaction of waves with inhomogeneous media leads to the natural focusing of light, the channelling of waves into stable caustics. We have extended natural focusing to x rays, observing caustics in topographs of ferroelectric lithium niobate. Voltage across domains of reversed polarity induces perturbations to the local crystal planes, producing dramatic variations in the images. Ray tracing shows a catastrophic discontinuity, causing bright focal lines. Analysis reveals details of boundary strains and local ferroelectric properties. Controlled focusing could be extended to designed domain patterns to probe microstructural properties, and also to a type of voltage-controlled ferroelectric optics for x rays. (c) 2007 American Institute of Physics