Photoinduced electric current in Fe-doped KNbO_3
Н. НогиноваN. KukhtarevT. KukhtarevaM. A. NoginovH. John CaulfieldPutcha VenkateswarluDavid ParkerPartha P. Banerjee
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Photorefractive KNbO3:Fe is characterized by monitoring of the electric currents induced in the crystal that are due to applied illumination. Important photorefractive parameter values, such as the Maxwell relaxation time, carrier-diffusion length, carrier-screening length, and the magnitude of the photogalvanic current are thereby estimated.Keywords:
Electric current
Photoconductivity
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In the past, the photorefractive properties of BaTiO 3 crystals doped with chromium [1] and iron [2, 3] have been described. Iron impurities, present in nominally undoped .crystals at levels between 40 and 150 ppm, have been identified as the microscopic centers correlated with the photorefractive effect [4]. The observed photorefractive effect in high purity crystals, however, with an iron level claimed to be smaller than 0.3 ppm [3], has been interpreted as evidence for another photorefractive species in these samples. The exact role of transition metal dopants in photorefractive BaTiO 3 is still unclear.
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The photoconductivity of BSO was investigated through the dependence of the photocurrent on wavelength and power. The variation of the photocurrent and the photorefractive effect as a function of the mode of illumination was determined. The evidence indicates that different transport mechanisms (with different transport parameters) are effective in the photoconductive and photorefractive effects. Hopping mechanisms appear to be important in charge transport in these materials.
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This review article describes the current state-of-the-art research on organic photorefractive polymer composites. A historical background on photorefractive materials is first introduced and is followed by a discussion on the opto-physical aspects and the mechanism of photorefractivity. The molecular design of photorefractive polymers and organic compounds is discussed, followed by a discussion on optical applications of the photorefractive polymers. This review article describes the current state-of-the-art research on organic photorefractive polymer composites. A historical background on photorefractive materials is first introduced and is followed by a discussion on the opto-physical aspects and the mechanism of photorefractivity. The molecular design of photorefractive polymers and organic compounds is discussed, followed by a discussion on optical applications of the photorefractive polymers.
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N.V. Kukhtarev and T. Kukhtarev, Optical and Electrical Properties of High Contrast Dynamic Gratings. S. Erdei, Growth and Characterization of Single-Crystal Photorefractive Fibers. P.A. Yeh, Cross-talk in Photorefractive Hologram Memory. D. Psaltis, Photorefractive Memory. F. Zhao, Spectral and Spatial Diffraction in a Nonlinear Photorefractive Hologram. S. Yin, Z. Wu, and D. McMillen, Specially Doped LiNbO3. K. Itoh, Dyamic Interconnections Using Photorefractive Crystals. P.P. Banerjee, N.V. Kukhtarev, and J.O. Dimmoctz, Nonlinear Self-Organization in Photorefractive Materials. S. Kawata, Three-dimensional Bit-memory Using Photorefractive Materials. A. Chiou, Phase Conjugate Microscopy for Optical Trapping and Image Processing. A. Yang, Three-dimensional Photorefractive Memory Based on Phase-code and Notation Multiplexings. J. Zhang and S. Yin, Dynamic Process of Photorefractive Holograms. F.T.S. Yu and S. Yin, Dynamics of Photorefractive Fiber Holograms and Applications. A.L. Mikaelian, Photorefractive Optics for Information Technology.
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Lithium niobate (LN) is attractive material for the frequency mixers and doublers, integrated optical devices, electro-optical modulators, holographic data recording and storage thanks to the acousto-optical, non-linear optical, piezo-electrical, electro-optical and photorefractive properties. However, the overall understanding of certain phenomena that is photorefractive effect occurring in the crystal is still under heavy discussion. The mentioned plays a key role: on one side it substantially restricted the main part of the wavelength conversion applications as when illuminated by visible light or near infrared, there are changes semi-permanent in the refractive index of the crystal, causing a distortion of the beam, greatly reducing the efficiency of the device, on the other hand it need to improve for holographic applications. The dissertation is devoted to the investigation of the photorefractive, structural, electro-optical (EO) and dielectrical properties depending on the intrinsic and extrinsic (introduced by incorporation of non photorefractive (〖Zr〗^(4+),〖In〗^(3+)) and photorefractive (〖Fe〗^(2+/3+)) ions) defects in LN crystals resulting to the purposeful control the photorefractive effect taking into account the features of the applications of LN crystals. The aim of the thesis is a development of a vision on advanced photorefractive and electro-optic properties in lithium niobate crystals doped with the transition metal and non-photorefractive ions on the basis of a full investigation of the structural, compositional, electro-optical, photorefractive properties of the mentioned crystals, to work out the parameters of a strong control of the photorefractive properties of this material and optimal conditions for the growth of high quality mentioned crystal with controlled physical properties and to grow this crystals as well.
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Ten years have passed since discovery of photorefractive polymer. This paper reviews the progress made respecting photorefractive polymers. The mechanism of the photorefractive effect in photorefractive polymers is also explained. Finally the applications of photorefractive polymers are described.
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Abstract : Photorefractive materials offer great promise for applications in optical data processing and phase conjugation using degenerate four-wave mixing. BaTiO3 is a particularly promising material, primarily because the very large value of the electro-optic tensor component r42 yields correspondingly large values of grating efficiency, beam coupling gain, and four-wave mixing reflectivity. Unfortunately, the commercial availability of BaTiO3 crystals is limited, and samples which are available are relatively small and impure and have not been characterized or optimized for photorefractive applications. In the program reviewed here, we have addressed two of the most important problems in the development and use of photorefractive BaTiO3: stabilization of the cubic phase in order to permit more rapid crystal growth than is now possible, and determination and characterization of the photorefractive species in commercial BaTiO3. The second major effort of this program was the identification and characterization of the photorefractive species in BaTiO3. Using the results of a number of experiments, we have concluded that iron (in the forms Fe2+ and Fe3+) is the dominant photorefractive species in commercial BaTiO3. We have been able to measure the densities of Fe2+ and Fe3+, along with the sign of the photocarriers, the effective electro-optic coefficient, and a lumped parameter taking into account the transport properties of holes and electrons.
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The article consists of two main parts: the first one contains a short summary of the photorefractive effect, discussing the phenomena and the main aspects related to practical applications, followed by a synopsis of the recent progress of photorefractive materials. The second part is devoted to one of the fastest photorefractive materials, sillenite inorganic crystals, focusing in particular on the enhanced photorefractive properties in the near‐infrared spectral range. Examples of real‐time data processing with significant recording speed, as well as realized quasi‐nondestructive holographic recording are also presented. Finally, photonic devices based on the photorefractive nonlinearity, such as optically addressed spatial light modulators and all optically controlled light valves, are discussed.
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We have used a number of experimental techniques to identify the photorefractive species in commercial samples of BaTiO3. We find that Fe impurities (in the Fe2+ and Fe3+ states) are the predominant photorefractive species. Techniques for optimizing the photorefractive properties of BaTiO3 are discussed.
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