Showing papers on "Organic photorefractive materials published in 2011"

Organic Photorefractive Materials and Applications

Abstract: This review describes recent advances and applications in the field of organic photorefractive materials, an interesting area in the field of organic electronics and promising candidate for various aspects of photonic applications. We describe the current state of knowledge about the processes involved in the formation of photorefractive gratings in organic materials and focus on the chemical and photo-physical aspects of the material structures employed in low glass-transition temperature amorphous composites and organic photorefractive glasses. State-of-the art materials are highlighted and recent demonstrations of photonic applications relying on the reversible holographic nature of the photorefractive materials are discussed.

Optical surface wave in a crystal with diffusion photorefractive nonlinearity

Abstract: We consider a steady-state nonlinear photorefractive surface wave (PR SW) with TE or TM polarisation when the refractive index of the photorefractive crystal (PRC) depends on the strength of the diffusion crystal electric field emerging upon the wave propagation. We have determined the phase trajectory and transverse structure of the PR SW intensity distribution for different values of the diffusion photorefractive nonlinearity. We have investigated a photorefractive diffraction grating, which arises in the surface PRC layer during propagation of the nonlinear PR SW.

Diffraction cancellation over multiple wavelengths in photorefractive dipolar glasses.

Abstract: We report the simultaneous diffraction cancellation for beams of different wavelengths in out-of-equilibrium dipolar glass. The effect is supported by the photorefractive diffusive nonlinearity and scale-free optics, and can find application in imaging and microscopy.

Infrared sensitive liquid crystal photorefractive hybrid cell with semiconductor substrates

Abstract: Refractive index grating recording is achieved in the infrared in a nematic liquid crystal placed between semiconductor CdTe substrates. Light-induced space-charge field created in photorefractive semiconductor substrates varies an alignment of liquid crystal molecules inhomogeneously in space forming a spatial modulation of the refractive index in liquid crystal. Two-beam coupling is studied in the hybrid cell, in which a gain factor Γ=16 cm−1 is achieved in the layer of liquid crystal of the sandwich.

Photorefractive and Raman Light Scattering in Lithium Niobate Ferroelectric Crystal

Abstract: Using the methods of photorefractive and Raman light scattering, we study subtle features of the structure of LiNbO3 single crystals with different Li/Nb ratios (pure and doped with nonphotorefractive cations) grown by different methods. We reveal that, upon the irradiation of a single crystal with visible laser light, locally fluctuating micro- and nanostructures are initially formed in it, with their physical parameters being different from the corresponding parameters of the single crystal in the absence of the photorefractive effect. Upon an increase in the irradiation intensity and in the course of time, more and more such micro-structures are formed, and they are transformed into static micro- and nanoformations, which are subsequently converted into a continuous laser track. The speckle structure of photorefractive scattering is studied in detail. We show that the photorefractive effect in single crystals of the stoichiometric composition is fairly strong for their use as materials for recording and storing information.

Slowdown and speedup of light pulses using the self-compensating photorefractive response

Abstract: We study theoretically the effects of pulse slowdown and speedup in ferroelectric Sn2P2S6 possessing a self-compensating photorefractive response. It is shown that both these effects can be implemented in one sample for sufficiently large values of the coupling strength. In contrast to other types of the photorefractive response (local and nonlocal), the output pulses do not suffer from strong spatial amplification and broadening.

Change of the refractive index in PPLN waveguides due to the photorefractive effect

Abstract: In this work we report the results of the experimental investigation of the refractive index change due to the photorefractive effect in periodically poled lithium niobate (PPLN) Ti-diffused waveguides in dependence on light intensity and sample temperature. We show an experimental method that allows for the direct determination of the refractive index change. The saturation state of the change of the refractive index is reached at 775 nm with input power of 50 μW.

Photoinduced electrokinetic redistribution of nano/microparticles during holographic grating recording in the ferroelectric crystal

Abstract: We have investigated photoinduced redistribution of metal nanoparticles, placed on the surface of the ferroelectric photorefractive crystal during recording of dynamic holograms. Motivations for this study were improvement of sensitivity for recording of dynamic holographic gratings, for application in nondestructive testing of materials. The home- made biosynthesized gold and silver colloidal solutions were spread as a thin layer on the ferroelectric photorefractive crystal surface. Holographic gratings were recorded in photorefractive crystal of Fe:LiNbO 3 (Fe:LN) by the HeNe laser (λ=633nm) to avoid direct influence of laser light on nanoparticles. Photorefractive holographic grating initially recorded in the crystal volume produce spatially modulated electric field on the crystal surface. This field led to electrophoretic redistribution of the nanoparicles on the crystal surface that result also in additional contribution to the electric field pattern and also change diffraction efficiency of hologram. In addition, we have recorded holographic grating in Fe:LN placed in 5mm cuvette with silver nanoparticles nanofluid and observed nanoparticles distribution along grating line. We have calculated electrophoretic (EP) and dielectrophoretic (DEP) forces on the crystal surface with holographic photorefractive grating, recorded in the crystal. It is shown that longitudinal (along the crystal surface) components of the DEP-force can be described only with high-contrast approach.

Four-wave mixing real-time intensity filtering with organic photorefractive materials

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. Some simulation results also are provided.

Influence of Photoconductivity on the Photorefractive Effect of Ferroelectric Liquid Crystal Mixtures

Abstract: The influence of photoconductivity on the photorefractive effect of ferroelectric liquid crystals (FLCs) was investigated. Mixtures of phenylpyrimidine derivatives, a chiral dopant, and a viscosity reducer were used as host FLC materials and two types of photoconductive compounds and an electron acceptor compound were added. The photorefractive effect was evaluated using two-beam coupling experiments. It was found that the magnitude of the gain coefficient was affected by the difference between the mobility of the photoconductive compound and that of the electron acceptor.

Photorefractive manipulation of plasmons in hybrid liquid crystal cells

Abstract: Surface Plasmon Polaritons (SPP) are of fundamental interest in a wide variety of applications including optical signal processing and sensing. The ability to manipulate these SPP is essential for continued development in this field. The high sensitivity of SPP to variations in the refractive index near the metal opens up the possibility of manipulating them using a photorefractive liquid crystal cell [1] adjacent to a thin gold layer, see Figure 1 (A).

Non-linear Control of Surface Plasmon Polaritons with Photorefractive Liquid Crystal Cells

Abstract: Photorefractive liquid crystal cells with a spatially varying refractive index are used to couple energy between surface plasmon modes. Presented are details on maximising this energy transfer and the behaviour of our liquid crystal cells.