P A Thomas

Publications (2)2.54 Total impact

• Article: Quantitative x-ray Bragg diffraction topography of periodically domain-inverted LiNbO3

  M Drakopoulos, Z W Hu, S Kuznetsov, A Snigirev, I Snigireva, P A Thomas
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  ABSTRACT: Periodic domain inversion in a ferroelectric material (lithium niobate) has been studied using high-resolution x-ray diffraction topography. A domain-inverted structure of period 30 µm was fabricated in a LiNbO3 crystal with a thickness of 300 µm via electric-field poling. The synchrotron-radiation x-ray experiments were carried out at the ESRF micro- fluorescence, imaging and diffraction beamline (ID22). The experimental topograms and numerical simulations show that the image contrast can be explained in terms of a phase shift of the polarizability coefficient, h, in the domain-inverted region relative to the non-inverted part. This phase shift, 1.72, was found to be equivalent to the reflection, 00, from the domain-inverted part of the structure rather than to the reflection, 006, from the non-inverted part. The numerical simulation shows that the width of the transition region between inverted and non-inverted domains (domain walls) is 0.3 µm.
  Journal of Physics D Applied Physics 12/1998; 32(10A):A160. · 2.54 Impact Factor
• Source

  Available from: A. Snigirev

  Article: Phase-mapping of periodically domain-inverted LiNbO3 with coherent X-rays

  Z W Hu, P A Thomas, A. Snigirev, I. Snigireva, A Souvorov, P G R Smith, G W Ross, S Teat
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  ABSTRACT: A varying refractive index across a wavefront leads to a change in the direction of propagation of the wave. This provides the basis for phase-contrast imaging of transparent or weakly absorbing materials with highly coherent X-ray beams. Lattice distortions can also change the direction of propagation of a wave field diffracted from a crystal. Here we report the use of this principle to effect phase-contrast imaging of the domain structure of a ferroelectric material, lithium niobate. A periodically domain-inverted structure for quasi-phase-matching of second-harmonic generation is created in this material, in which the direction of spontaneous polarization is sequentially inverted. Because of complex interactions during domain-inversion processing, this is accompanied by lattice distortions across the domain walls. These distortions split the diffracted wavefront of a beam of coherent X-rays from an advanced synchrotron source, giving rise to a pattern of interference that reflects the underlying pattern of lattice distortions. These results show that this phase-contrast imaging technique with sub-micrometre spatial resolution permits the non-destructive, highly sensitive phase-mapping of various structural defects and distortions introduced into materials during processing.