Topic
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.
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28 May 1999
TL;DR: In this article, the authors reported the use of soliton formation to create permanent waveguides by selectively reorienting ferroelectric domains within the incident light beam, via the Pockels effect.
Abstract: Summary form only given. Optical spatial solitons in photorefractive crystals have shown the potential to form optical circuitry by forming graded index waveguides which can guide other beams. A soliton forms when a photoinduced index change in the material exactly compensates for the diffraction of the beam; i.e. the beam creates its own waveguide. In photorefractive materials, a screening soliton is formed by applying an external electric field that within the incident light beam is screened by photoinduced charges. The external field then lowers the refractive index around the screened area, via the Pockels effect, creating a waveguide. However, these induced waveguides disappear if the applied field is removed from the material. In the paper we report on the use of soliton formation to create permanent waveguides by selectively reorienting ferroelectric domains within the incident light beam.
28 Aug 1994
TL;DR: In this article, a finite difference technique was used to model the photorefractive grating formations and provide more detailed numerical analysis for the first time, including both diffraction and energy transfer, in BSO as function of modulation index and fringe velocity.
Abstract: but only in the limit of small modulation. In practice, most experimental conditions cannot be adequately described by the linearized theory. The correction function used by Refregier et al.' describes the effect of modulation, but only for twowave mixing at the optimum velocity. Au and Solyma? have demonstrated numerically a complicated photorefractive response. In this paper we provide more detailed numerical analysis, and for the first time, experimental characterization of the photorefractive response, including both diffraction and energy transfer, in BSO as function of modulation index and fringe velocity. A finite difference technique was used to model the photorefractive grating formations. This approach calculated the full space charge field within the resolution of the element size, providing spatial and temporal evolution of the space charge field up to modulation m = 1. The experimental arrangement utilized an argon-ion or a double Nd:YAG laser to write the holograms. A HeNe laser was used in the non-degenerate four-wave mixing configuration to measure the diffraction efficiency. At large modulation the space charge field characteristics exhibited a complicated dependence on the fringe velocity, as demonstrated for the case of m = 0.9 in Fig. 1, where the calculated amplitude, phase, and imaginary part of the fundamental component of the space charge field are plotted versus normalized velocity. Here vOpt is the resonant velocity at small modulation. Experimental results are shown in Fig. 2, which compare the measured two-beam coupling gain and diffraction efficiency as a function of fringe detuning. The optimum frequency at small modulation was 2.4 Hz. The fringe velocity that optimized the diffraction efficiency depended strongly on modulation index, particularly at very large modulation, and was not always the same as the optimum velocity for energy transfer. In general, the optimum velocity for diffraction increased with increasing modulation, but at very large modulation shifted to very small fringe velocities. This effect is demonstrated in Fig. 3. , The numerical results predict the saturation in the two-wave mixing associc ._ ?. 0.6 1
16 Jul 1990
24 Apr 2008
TL;DR: In this paper, the first step in the optical recording process in these materials is the building up of a spatial modulation of electric charges via charge carriers excitation from localized to extended states where they diffuse and/or are drifted and then retrapped in a localized state.
Abstract: Photorefractive materials exhibit photoconductive and electro‐optic properties. The first step in the optical recording process in these materials is the building up of a spatial modulation of electric charges via charge carriers excitation from localized to extended states where they diffuse and/or are drifted and then retrapped in a localized state. In this way the pattern of light onto the sample is converted into a spatial modulation of charges and its corresponding space‐charge electric field produces a volume index‐of‐refraction modulation via electro‐optic effect. The latter is the resulting volume phase hologram. The position of the photoconductive centers in the localized states in the material band gap as well as the density and properties of the donor/acceptor centers and charge carriers transport properties are therefore important parameters characterizing the materials and determining their performance as far as optical recording is concerned. For determining these parameters we use optical, ...
12 Nov 2001
TL;DR: By doping nonlinear optical chromophores into liquid crystals, the threshold voltage could be reduced significantly and the mechanism involved was investigated in this article, which is attributed to reorientation of liquid crystal molecules by light induced space-charge field.
Abstract: Photorefractive effect in nematic liquid crystals is attributed to reorientation of liquid crystal molecules by light induced space-charge field. In the absence of external field, nematic liquid crystals form domain structure, which is responsible for high threshold voltage. By doping nonlinear optical chromophores into liquid crystals, the threshold voltage could be reduced significantly and the mechanism involved was investigated.