Optical and thermal control of domain structures in ferroelectric crystals
This thesis presents the results of investigations into the thermal and optical control of ferroelectric domains within lithium tantalate and strontium barium niobate crystals. The aim of the work was to develop techniques for optically pattering domain inverted structures within ferroelectric crystals. Initial studies involving strontium barium niobate revealed an enhanced temperature sensitivity for transient repoling occurring at room temperatures for this material. This has important consequences for the optical manipulation of domains in this material. Further work indicated that the optical control of domains in this material were limited by the variation in crystal properties of strontium barium niobate crystals. Subsequent work concentrated on lithium tantalate, in which domain pattering was successfully accomplished at room temperature via the simultaneous application of optical and electric fields. The technique consisted of illuminating the x-face of a 200 μm thick lithium tantalate z-cut crystal which had been polished to form a biprism. The resulting interferometric pattern, formed between planar electrodes applied to the +z and -z crystal faces, had a period of ~6 μm. This optical pattern defined where poling occurred by effectively increasing the coercive field within the illuminated regions of the crystal. This effect was used to inhibit ferroelectric switching within the illuminated regions so that the optical pattern is thereby translated into a corresponding domain structure. The increase in coercive field is a consequence of internal field relaxation within the crystal, for which the underlying principles of light induced ferroelectric switching are addressed. This is the first demonstration of optical periodic domain pattering using interferometric techniques.