Organic photorefractive materials

About: Organic photorefractive materials is a research topic. Over the lifetime, 697 publications have been published within this topic receiving 13041 citations.

Self-action of light beams in planar waveguides on photorefractive crystal

Abstract: Self-action of light beams in photorefractive waveguides is theoretically and experimentally investigated. We consider the waveguide formed by sequential diffusion of titanium and iron in Z-cut of LiNbO3 and the biased waveguide Bi12TiO20 on Bi12SiO20. It is shown that the spatial averaging of nonlinear change of refractive index is valid for different mechanisms of photorefractive effect. The wave equation in parax-ial approximation for evolution of beam amplitude shape is derived. We determine the conditions of the soliton formation for different waveguide modes taking into account two-dimensional distribution of optical field in guiding layer and the overlap integral of this field with the nonlinear changes in refractive index.

Photorefractive polymers with improved efficiency

Abstract: Recently, photorefractive polymers have emerged as promising recording media for holographic storage and optical processing such as optical correlation devices.',' Because of their structural flexibility, these new materials could be optimized and materials with fully reversible refractive index modulation of An = 7 X 10K3 have been developed leading to nearly 100% diffraction efficiency in 105-pmthick samples.' However, the high electric field that needs to be applied (50-100 V/pm) to these polymers to reach that level of performance is a limitation. Thus there is a need for photorefractive polymers doped with more efficient chromophores. Here, we present a new photorefractive polymer composite based on a PVK matrix and doped with the new chromophore HR-254. The photorefractive properties of these new composites are studied by four-wave mixing and two-beam coupling experiments. The chromophore, whose structure is shown in the inset of Fig. 1, has been designed to lead to an efficient orientational effect in low glass transition temperature ( T,) photorefractive polymers. The chromophore has an absorption maximum at 500 nm as shown in Fig. 1. The structure of the molecule has been carefully designed to prevent photoisomerization and to ensure good solubility in the photoconducting matrix and to prevent crystallization. The nonlinear response of the chromophore was measured with the frequency-dependent ellip-

Picosecond Dynamics of Free-Carrier Populations, Space-Charge Fields, and Photorefractive Nonlinearities in Zincblende Semiconductors

Abstract: Generally, nonlinear optics studies investigate optically-induced changes in refraction or absorption, and their application to spectroscopy or device fabrication. The photorefractive effect is a nonlinear optical effect that occurs in solids, where transport of an optically-induced free-carrier population results in an internal space-charge field, which produces an index change via the linear electrooptic effect. The photorefractive effect has been widely studied for a variety of materials and device applications, mainly because it allows large index changes to be generated with laser beams having only a few milliwatts of average power.Compound semiconductors are important photorefractive materials because they offer a near-infrared optical response, and because their carrier transport properties allow the index change to be generated quickly and efficiently. While many researchers have attempted to measure the fundamental temporal dynamics of the photorefractive effect in semiconductors using continuous-wave, nanosecond- and picosecond-pulsed laser beams, these investigations have been unsuccessful. However, studies with this goal are of clear relevance because they provide information about the fundamental physical processes that produce this effect, as well as the material's speed and efficiency limitations for device applications.In this dissertation, for the first time, we time-resolve the temporal dynamics of the photorefractive nonlinearities in two zincblende semiconductors, semi-insulating GaAs and undoped CdTe. While CdTe offers a lattice-match to the infrared material HgxCd1-xTe, semi-insulating GaAs has been widely used in optoelectronic and high-speed electronic applications. We use a novel transient-grating experimental method that allows picosecond temporal resolution and high sensitivity. Our results provide a clear and detailed picture of the picosecond photorefractive response of both materials, showing nonlinearities due to hot-carrier transport and the Dember space-charge field, and a long-lived nonlinearity that is due to the EL2 midgap species in GaAs. We numerically model our experimental results using a general set of equations that describe nonlinear diffraction and carrier transport, and obtain excellent agreement with the experimental results in both materials, for a wide variety of experimental conditions.

Light scattering in single crystals of nonlinear-optical photorefractive LiNbO3:Cu and LiNbO3:Zn

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.

Advances in organic photorefractive materials development

Abstract: We present results on the photorefractive performance of two different classes of organic materials. One of them is based on the space-charge field induced reorientation of the optical axis of chiral smectic A phases. In this case the orientational effect is linear in the field and it is due to the so-called electroclinic effect, in contrast with the quadratic effect present in nematics and associated with dielectric anisotropy. Besides presenting data on the photorefractive properties of these new mesophases, we will consider a simple model which describes their performance as a function of several material and geometrical parameters. In the second part of the paper we introduce cyclopalladated complexes as a new class of multifunctional photorefractive materials. Such molecules form amorphous phases which are photoconducting and exhibit a field dependent refractive index. Their efficiency is among the best known to date for organic materials and the simple synthetic route makes us foresee a fast optimization of cyclometallated compounds for photorefractive applications.