PHASE-MAPPING OF PERIODICALLY DOMAIN-INVERTED LINBO3 WITH COHERENT X-RAYS

A varying refractive index across a wavefront leads to a change in the direction of propagation of the wave(1,2). This provides the basis fo r phase-contrast imaging of transparent or weakly absorbing materials with highly coherent X-ray beams(3,4). Lattice distortions can also ch ange the direction of propagation of a wave field diffracted from a cr ystal. Here we report the use of this principle to effect phase-contra st imaging of the domain structure of a ferroelectric material, lithiu m niobate. A periodically domain-inverted structure for quasi-phase-ma tching of second-harmonic generation is created in this material, in w hich the direction of spontaneous polarization is sequentially inverte d. Because of complex interactions during domain-inversion processing, this is accompanied by lattice distortions across the domain walls. T hese distortions split the diffracted wavefront of a beam of coherent X-rays from an advanced synchrotron source, giving rise to a pattern o f interference that reflects the underlying pattern of lattice distort ions. These results show that this phase-contrast imaging technique wi th sub-micrometre spatial resolution permits the non-destructive, high ly sensitive phase-mapping of various structural defects and distortio ns introduced into materials during processing.