Showing papers on "Organic photorefractive materials published in 1988"
TL;DR: In this paper, the photorefractive effects of nominally pure and iron-doped KNbO3 crystals with concentrations between 150 and 300 ppm were investigated with a two-carrier model.
Abstract: Photorefractive effects of nominally pure and iron‐doped KNbO3 crystals with concentrations between 150 and 300 ppm have been investigated. In order to optimize the photorefractive recording times and the amplitude of the refractive changes, the crystals were thermally treated with simultaneous photorefractive testing. The photoconductivity data and the photorefractive experiments (grating spacing dependence of the beam coupling gain) show that the relative influence of electron and hole contribution is altered depending on the reduction treatment. The experimental results are discussed with a two‐carrier model.
70 citations
TL;DR: In this paper, a model that provides a means for understanding the effects of crystal growth and processing conditions on the photorefractive properties of BaTiO3 was presented, based on a thermodynamic point defect model that allows for the existence of transition-metal dopants in multiple valence states and for the incorporation of more than one species with levels in the band gap.
Abstract: We present a model that provides a means for understanding the effects of crystal growth and processing conditions on the photorefractive properties of BaTiO3. The densities of photorefractive centers are calculated from a thermodynamic point defect model. This model allows for the existence of transition-metal dopants in multiple valence states and for the incorporation of more than one species with levels in the band gap. Beam-coupling gain and response time are calculated as a function of temperature and oxygen partial pressure of treatment for various dopant types and concentrations. The predicted behavior is compared with existing experimental data on BaTiO3 crystals, and implications for improving the photorefractive performance are discussed.
48 citations
TL;DR: In this article, a set of nonlinear coupled differential equations is used to solve the interaction between optical beams incident upon and generated within a photorefractive material. And the mechanism of the emergence of a higher diffraction order is explored in particular, under favorable conditions, a significant amount of power may be transferred to the nearest higher-order wave.
Abstract: Interactions between optical beams incident upon and generated within a photorefractive material are investigated by numerically solving a set of nonlinear coupled differential equations The mechanism of the emergence of a higher diffraction order is explored In particular, it is shown that, under favorable conditions, a significant amount of power may be transferred to the nearest higher-order wave >
36 citations
TL;DR: In this article, the photorefractive effect in 4 3 m crystals shows specific symmetries in its dependence upon wave polarizations and crystal orientation, and theoretical predictions and experimental verification in semi-insulating gallium arsenide in the nanosecond regime at 1.06 μm are given.
25 citations
TL;DR: In this article, a system of nonlinear equations is solved to describe a four-wave interaction in photorefractive media generating transmission or reflection refractive index gratings in the case of a drift-diffusive nonlinearity mechanism with an arbitrary complex coupling constant.
Abstract: A system of nonlinear equations is solved to describe a four-wave interaction in photorefractive media generating transmission or reflection refractive index gratings in the case of a drift-diffusive nonlinearity mechanism with an arbitrary complex coupling constant. An analysis is made of the four-wave interaction in the geometry of a nonlinear ring resonator where a reflection grating is formed.
15 citations
TL;DR: In this paper, the magnitude and time evolution of refractive index gratings are monitored via diffraction, and quantitative information concerning the spatial variation of dark conductivity, photoconductivity, and deep level absorption can be extracted.
Abstract: Making use of the photorefractive effect, we have developed a versatile method of imaging various crystal properties of semi‐insulating compound semiconductors. The magnitude and time evolution of refractive index gratings are monitored via diffraction. The observed diffraction is directly related to the electric fields present, and quantitative information concerning the spatial variation of dark conductivity, photoconductivity, and deep level absorption can be extracted. Wafers of undoped GaAs and InP:Fe have been characterized in this manner, and comparisons of images are made which demonstrate the capabilities of this technique.
9 citations
01 Dec 1988
TL;DR: In this article, the authors investigate the photorefractive effect of non-uniform light intensity patterns in the material and identify a new important consideration in the theory of two-wave mixing between counter-propagating beams.
Abstract: : Photorefractive crystals are materials whose index of refraction is altered under illumination by light. These crystals are both photoconductive and electrooptic. When a nonuniform light intensity pattern is present in the material, photocarriers are generated and redistributed, creating space charge electric fields which change the refractive index locally. These crystals are ideal media for real time holography, and applications include wave amplification, image processing, phase conjugation, and laser beam steering for optical interconnects. This thesis investigates many novel aspects of the photorefractive effect. A study of nonreciprocal behaviour identifies a new important consideration in the theory of two-wave mixing between counterpropagating beams-namely the presence of a photocurrent, or frequency detuning between the beams results in a spatially varying beam coupling. A numerical treatment of these important cases provides the first systematic theoretical assessment the control of nonreciprocal transmission and phase shift in lithium niobate, a representative photorefractive crystal. A comparison between crystal types suggests candidates for nonreciprocal applications such as an optical diode. Theses.
1 citations
Proceedings Article•
25 Apr 1988TL;DR: For a given beam intensity, the response time of GaAs is 2 orders of magnitude taster than those of conventional photorefractive materials as discussed by the authors, which shows that GaAs has several potential advantages over other conventional materials such as barium titanate, barium strontium niobate, and bismuth silicon oxide.
Abstract: GaAs is a technologically important material for high-speed electronics, laser, and sensor applications. It also could play an important role in optical processing as a photorefractive medium. GaAs has several potential advantages over conventional photorefractive materials, such as barium titanate, barium strontium niobate, and bismuth silicon oxide. For a given beam intensity, the response time of GaAs is ~2 orders of magnitude taster than those of conventional photorefractive materials.1
1 citations