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Showing papers on "Organic photorefractive materials published in 2010"


Journal ArticleDOI
TL;DR: A comprehensive, satisfactory explanation of most important questions on photorefractive optical damage is provided: photovoltaic currents, refractive index changes and, especially relevant, in degraded beam-profiles.
Abstract: Photorefractive optical damage of single beams in LiNbO(3) crystals is analyzed within a framework of two photoactive centres (Fe(2+)/Fe(3+) and Nb(Li) (4+)/Nb(Li) (5+)). It compares model simulations and significant experimental measurements in LiNbO(3) waveguides. A good agreement is found in the performed comparisons: photovoltaic currents, refractive index changes and, especially relevant, in degraded beam-profiles. The progress of the degraded wavefront has been simulated by implementing a finite-difference beam-propagating method which includes the model equations. These results, together with previous ones on grating recording, provide a comprehensive, satisfactory explanation of most important questions on photorefractive optical damage.

26 citations


Journal ArticleDOI
TL;DR: Alq(3) improves the response time, efficiency, and breakdown voltage without a significant increase in absorption or loss of phase stability, which has applications for reflection displays and pulsed writing.
Abstract: The electron transporting molecule tris(8-hydroxyquinoline) aluminum (Alq(3)) was added in low concentrations to a photorefractive polymer composite to provide trapping sites for electrons. This sample exhibited larger two-beam coupling gain, higher diffraction efficiency at lower voltages, and an increased dielectric breakdown strength compared to a control sample. The dynamics also revealed the presence of a competing grating, and a bipolar charge transport model is shown to fit the data. Overall, Alq(3) improves the response time, efficiency, and breakdown voltage without a significant increase in absorption or loss of phase stability. This has applications for reflection displays and pulsed writing, where charge trapping and generation are major factors limiting the usefulness of photorefractive polymers.

20 citations


Journal ArticleDOI
TL;DR: In this article, the authors analyzed the photorefractive dependence of two-beam coupling between the pump beam and the signal beam in a non-degenerate wave mixing under the undepleted pump approximation method.
Abstract: Photoconductive dependence of two-beam coupling between the pump beam and the signal beam in photorefractive materials have been analyzed in case of non-degenerate wave mixing under the undepleted pump approximation method. During the two-wave mixing in photorefractive materials, steady state amplification of the signal beam and oscillation characteristics of a single unidirectional ring resonator has been studied. The domination of the two-beam coupling gain over the combined absorption and resonator losses such as Fresnel reflections from the crystal and imperfect mirrors builds up unidirectional oscillation. The buildup of such an oscillation leads to a saturation of the gain, which can be explained in terms of the photorefractive phase-shift. The existence of this phase-shift between the photorefractive index grating and the illumination intensity pattern, which is of characteristic of the photorefractive effect, leads to an energy transfer between the two beams. For a single unidirectional ring resonators, the effects of photoconductivity of the materials, two-beam energy coupling coefficient, dielectric constant, crystal thickness, and material's absorption coefficient on amplification of the two-beam coupling gain and photorefractive phase-shifts of the signal beam have also been studied in detail. It has been found that amplification of the signal beam and phase-shift can be enhanced by taking the photorefractive crystal having higher photoconductivity and lower dielectric constant, which improves performance of the resonators.

11 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of carbon nanotubes (CNTs) on photoinduced changes in refractive index, non-linear refraction, and nonlinear third-order optical susceptibility in organic materials based on polyimides, pyridines, and prolinols is briefly considered.
Abstract: The phenomenon of a significant increase in the photoinduced changes in refractive index, non-linear refraction, and nonlinear third-order optical susceptibility in organic materials based on polyimides, pyridines, and prolinols upon the introduction of fullerenes and carbon nanotubes (CNTs) into the organic matrix is briefly considered (with emphasis on the dominating effect of CNTs) It is established that the values of these photorefractive parameters determined in said fullerene- and CNT-doped materials using a four-wave-mixing scheme are close to the analogous values in bulk silicon-based materials The results can be useful in developing thin-film nonlinear filters, thin diffraction gratings for passive data recording, and optically-addressed light modulators, in medical applications, and in display technology (eg, for creating a three-dimensional medium prototype)

5 citations


Journal ArticleDOI
TL;DR: In this paper, the authors theoretically studied photorefractive surface waves supported by polymers with orientationally enhanced photore-fractive effect and found that the profile, frequency and especially the penetration depth of polymeric photoreflourish surface waves strongly depend on external electric field, which makes it more controllable than that in polymeric inorganic crystals.

5 citations


Journal ArticleDOI
TL;DR: The observation of the photorefractive effect in undoped aluminum nitride and an absorption grating was also formed, which is attributed mainly to an ionized trap density modulation process.
Abstract: We report our observation of the photorefractive effect in undoped aluminum nitride. We measured the coupling constant and the formation rate as a function of pump intensity at a wavelength of 405 nm in a two-wave mixing experiment. The photorefractive gain coefficient was 0.47 cm−1 at I = 6.9 W/cm2, and the actual saturated value was probably larger than this. The time constant was 59 ms at I = 1.0 W/cm2. In addition to a refractive index grating, an absorption grating was also formed, which is attributed mainly to an ionized trap density modulation process.

3 citations


Journal ArticleDOI
TL;DR: In this article, a theory of photorefractive effect in organic PR materials based on exciton formation, diffusion, and dissociation in organic polymer semiconductors is presented, and exact numerical and approximate analytical solutions of the model indicate that an increase in the exciton diffusion constant reduces the amplitude of the resulting space-charge electric field.
Abstract: A theory of photorefractive (PR) effect in organic PR materials based on exciton formation, diffusion, and dissociation in organic polymer semiconductors is presented. The exact numerical and approximate analytical solutions of the model indicate that an increase in the exciton diffusion constant reduces the amplitude of the resulting space-charge electric field. The model also shows that a space-charge field is produced even in the absence of traps, and particular combinations of the detrapping rates and the trap depths could be used to enhance the space-charge field. It is suggested that an organic semiconductor with a smaller exciton diffusivity and traps with optimal detrapping rates would be a better candidate for photorefractivity.

3 citations


Journal ArticleDOI
Xiangkui Ren1, Tianhao Zhang1, Huihui Ma1, Weiwei Shao1, Jingjun Xu1, Jianguo Tian1 
TL;DR: The spatial frequency of photorefractive surface waves can be changed by an applied external electric field, which indicates a method for transforming the surface waves between high-frequency modes and low-frequency mode.
Abstract: We present the evolution equation of surface waves due to the two-photon photorefractive effect. It is shown theoretically that the surface waves can be supported by two-photon photorefractive media. The spatial frequency of photorefractive surface waves can be changed by an applied external electric field, which indicates a method for transforming the surface waves between high-frequency modes and low-frequency modes.

1 citations


Journal ArticleDOI
TL;DR: In this article, the authors predict the formation of electrically and optically controlled photorefractive surface waves in liquid crystal, with orientational photore-fractive effects.
Abstract: We predict the formation of electrically and optically controlled photorefractive surface waves in liquid crystal, with orientational photorefractive effects. In contrast to the case for photorefractive surface waves in inorganic crystals, the penetration depth of photorefractive surface waves in liquid crystal can be controlled by means of the applied external electric field, while the position of the photorefractive surface waves in the liquid crystal can be controlled by means of the applied external electric field and the polarization of incident light beams.

1 citations


Journal ArticleDOI
TL;DR: In this article, the photorefractive mechanism of light beam self-action in nematic liquid crystals was investigated, which consists in a decrease in the density of surface charges screening an external electric field upon light exposure.
Abstract: Photocurrents in liquid crystal cells of different structures were experimentally studied. The results of the study confirm the photorefractive mechanism of the light beam self-action in nematic liquid crystals, which consists in a decrease in the density of surface charges screening an external electric field upon light exposure. The data obtained from photoelectric and optical measurements suggest that the photorefractive effect appears in cells with different orientants and in the absence of orientant. In a planar cell oriented by rubbed polyimide, the crucial role is played by the interface between the liquid crystal and polyimide deposited on the anode.

1 citations


Journal ArticleDOI
TL;DR: In this article, the photorefractive scattering of light in nonlinear single crystals of lithium niobate with congruent compositions (LiNbO3) doped with "photore-fractive" Cu [0.015 mass %] and "non-photorefractional" Zn [ 0.5 mass %].
Abstract: Comparative studies are made of the photorefractive scattering of light in nonlinear single crystals of lithium niobate with congruent compositions (LiNbO3) doped with "photorefractive" Cu [0.015 mass %] and "nonphotorefractive" Zn [0.5 mass %] cations. For the first time it is found that single crystals doped with "photorefractive" and "nonphotorefractive" cations have different indicatrices for photorefractive light scattering. The aperture angle for photorefractive scattering reaches its steady state value more rapidly with high laser powers than with low. However, at high powers laser induced heating of the crystal is greater, and this leads to a narrowing of the scattering indicatrix. It is also found that photorefractive scattering in these single crystals depends on the region of the boule from which a sample has been cut. This indicates that there is a nonuniform distribution over the boule of the imperfections with localized electrons which determine the magnitude of the photorefractive effect.

Proceedings ArticleDOI
TL;DR: In this paper, the authors exploit the nonlinearity inherent in four-wave mixing in organic photorefractive materials and demonstrate edge enhancement, contrast conversion, and defect enhancement in a periodic structure.
Abstract: In this paper, we exploit the nonlinearity inherent in four-wave mixing in organic photorefractive materials and demonstrate edge enhancement, contrast conversion, and defect enhancement in a periodic structure. With the availability of these materials, which have large space-bandwidth products, edge enhancement, contrast conversion and defect enhancement are possible.

Journal ArticleDOI
TL;DR: In this article, a change in the refractive index of a photorefractive barium-sodium niobate crystal in an alternating electric field during the propagation of intensity-modulated coherent radiation in it is studied.
Abstract: A change in the refractive index of a photorefractive barium-sodium niobate crystal in an alternating electric field during the propagation of intensity-modulated coherent radiation in it is studied. It is shown experimentally that a change in the refractive index in the soliton regime in a photorefractive crystal with a small nonlocal response is independent of the external-field amplitude and intensity-modulation depth.

Journal ArticleDOI
TL;DR: The relationship between the thermal properties and the photorefractive effect of various ferroelectric liquid-crystal compositions was investigated in this article, where a mixture of phenyl pirimidine derivatives were used as host liquidcrystal materials to which chiral dopants and photoconductive compounds were added.
Abstract: The relationship between the thermal properties and the photorefractive effect of various ferroelectric liquid-crystal compositions was investigated. Mixtures of phenyl pirimidine derivatives were used as host liquid-crystal materials to which chiral dopants and photoconductive compounds were added. The photorefractive two-beam coupling gain coefficient was strongly dependent on the magnitude of spontaneous polarization and the uniformity of the surface-stabilized state.