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-focusing in photorefractive two-wave-mixing in drift- and diffusion-type material

Abstract: We report experimental results on self-focusing and self-defocusing of light in two-wave-mixing. The complex coupling coefficient for two-wave-mixing and the corresponding first-order (linear) and nonlinear (third-order) susceptibility were derived. Amplification and self-focusing were measured as functions of the frequency shift between signal and pump beam in two-wave-mixing in BSO and BaTiO/sub 3/. The frequency dependence of the self-focusing is found to have a dispersion shape as is plausible from the analogy of the photorefractive and the laser amplification. In a drift-type material, the self-focusing in two-wave-mixing has to be distinguished from photorefractive self-focusing. This is possible because two-wave-mixing self-focusing requires coherent fields, while photorefractive self-focusing does not. We were able to observe pure two wave-mixing self-focusing by using pump/signal ratios above 10, at which value the photorefractive self-focusing is suppressed. The self-focusing in two-wave-mixing in diffusion-type material (BaTiO/sub 3/) is isotropic in the transverse plane, whereas in the case of drift-type material (BSO) we found that the amount of self-focusing in two-wave-mixing is larger by a factor of about three along the direction of the external field than along the direction perpendicular to the external field. This anisotropy can be explained by pump depletion in BSO. Consequences of gain saturation for the measurements of self-focusing in BaTiO/sub 3/ are discussed. In general two-wave-mixing self-focusing can be changed to defocusing by a change of frequency shift between signal and pump beam and by a change of orientation of the crystal.

Investigation of temporal and spatial charge dynamics by wave mixing techniques

Abstract: Summary for only given. Under spatially non-uniform photoexcitation of photorefractive crystal, a diffusive transport of high mobility carriers (electrons) builds-up a space charge field (SC) which later affects the spatial distribution both of electrons and holes. Recent studies on free carrier (FC), photorefractive (PR), and absorptive nonlinearities in GaAs and CdTe:V revealed variety of effects related to the room-temperature EL2 defect metastability and defect-association assisted carrier generation.

Energy transfer between surface plasmon polariton modes with hybrid photorefractive liquid crystal cells

Abstract: In this thesis, a hybrid photorefractive liquid crystal cell structure with the addition of a thin 40nm Gold layer is proposed that demonstrates significant photorefractive control of Surface Plasmon Polaritons (SPP). The photorefractive effects are generated through optically controlling the conductivity of a ~100nm photoconducting poly-N-vinyl-carboxyl (PVK) layer. Therefore, when a potential is applied across the cell, the liquid crystal alignment and the SPP wavevector is able to be controlled with light. The aim for developing this device is for the eventual demonstration of SPP gain to offset the high optical losses and increase the characteristically short propagation length of SPP. The mechanism we intend to use to demonstrate gain is analogous to the asymmetric energy transfer in a wave mixing system for two laser beams used to typically characterise photorefractive materials. We first characterise the electrical and optical behaviour of the novel photorefractive plasmonic structure proposed with uniform illumination. Our system demonstrates a good photorefractive wavevector shift of 0.207µm-1 for a 1.24eV SPP; this shift is in excess of the FWHM of the SPP resonance in the attenuated total reflection spectrum (0.154µm-1). However, the electric behaviour of the system is found to be highly complex and cannot be fully characterised by an equivalent electrical circuit. In addition, due to electronic stability issues, we require a slow AC potential to demonstrate consistent photorefractive effects. In a step towards realising SPP gain, we then consider the SPP interaction with a refractive index grating written into the liquid crystal layer with the interference pattern of crossed laser beams. We find that a SPP is diffracted into additional SPP modes. Our investigation then determines the ideal parameters that maximise the energy transfer by examining the diffraction efficiency dependence of each variable of the system. The maximum energy transfer observed is 25.3±2.3% for a 1.05eV SPP from a 4µm grating. With the assistance of a numerical simulation of our system we present a series of qualitative and semi-analytical descriptions to describe the mechanisms behind the observed trends. We discover that the diffraction efficiency is dependent of three important effects; the orientation of the grating, the penetration depth of the SPP into the liquid crystal and the magnitude of the periodic electric field in the liquid crystal. In addition, to fully describe the quantitative values observed we must also consider the presence of a thin 100nm region of the liquid crystal near the photoconductor interface that does not strongly respond to the applied electric field due to anchoring forces.

Optical Image Cross Connector with Multiple-layered Photorefractive Polymers

Abstract: We propose an image cross connector with multiple-layered photorefractive polymers that arbitrarily changes and interconnects vertically-disposed input images into horizontally without blur We verify its fundamental operation with a photorefractive polymer PATPD experimentally

Orientational photorefractive effect in photosensitive-dye doped nematic liquid crystals

Abstract: Theoretical analysis of photorefractivity in dye-doped nematic liquid crystal film is discussed. Analytical solutions of refractive index distribution and the first order diffraction efficiency are presented. The relationship between the diffraction efficiency and the applied DC voltage shows very good agreement to the experimental result in photorefractive region.