Investigations of the photorefractive effect in potassium tantalum niobate

Citation

Leyva, Victor (1991) Investigations of the photorefractive effect in potassium tantalum niobate. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/cayt-6896. https://resolver.caltech.edu/CaltechETD:etd-11152005-081932

Abstract

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. This thesis describes results of investigations of the photorefractive effect in potassium tantalum niobate ([...]) crystals. A band transport model is used to describe the photorefractive effect. The coupled mode equations are then introduced and used to solve self-consistently for the interaction of the light and space charge fields in a photorefractive material. The design and construction of a high temperature crystal growth system is discussed. The growth of photorefractive KTN crystals doped with a variety of transition metal dopants using the top seeded solution growth method is described. Two applications in the areas of volume holography are described which take advantage of the unique ferroelectric properties of KTN. The first makes use of the quadratic electrooptic effect in paraelectric KTN to control the magnitude of a diffracted wave with an externally applied field. Full amplitude modulation at speeds much faster than the grating formation time demonstrated. The second application described is a procedure used to fix a holographic diffraction grating in KTN. It invovles the writing of a photorefractive grating in the paraelectric phase of KTN and cooling the sample under an applied field through successive phase transitions into the rhombohedral phase. Materials investigations of the photorefractive effect are described. Investigations focused on the optimization of the photorefractive properties of IKTN by the control of the concentration and the valence state of the photorefractive donor ions both during and after the growth stage. Absorption, photoconductivity, and electron microprobe measurements are used to identify the photorefractive species and to determine all relevant parameters which enter into the band transport model in a KTN:CuV sample after a series of thermal oxidation and reduction treatments. Holographic diffraction measurements are compared with those expected from theory. The oxidation and reduction process is modelled. Approaches to optimize the photorefractive sensitivity are discussed. The photorefractive properties of Fe and Ti doped KTN samples are investigated. Absorption and photoconductivity measurements indicate that the double dopant combination of Fe and Ti leads to an increased [...] and total Fe concentrations as compared to single doped samples. A corresponding increase in photorefractive sensitivity is measured. The dependence of the photorefractive properties of Fe and Ti doped KTN on electric field, grating period, and temperature is characterized.

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