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Takeo Sasaki - One of the best experts on this subject based on the ideXlab platform.

  • Photorefractive Effect in ferroelectric liquid crystals
    Optical Review, 2014
    Co-Authors: Takeo Sasaki, Yumiko Naka
    Abstract:

    In this paper, we review recent progress of research on the Photorefractive Effect of ferroelectric liquid crystals. The Photorefractive Effect is a phenomenon that forms a dynamic hologram in a material. The interference of two laser beams in a Photorefractive material establishes a refractive index grating. This phenomenon is applicable to a wide range of devices related to diffraction optics including 3D displays, optical amplification, optical tomography, novelty filters, and phase conjugate wave generators. Ferroelectric liquid crystals are considered as a candidate for practical Photorefractive materials. A refractive index grating formation time of 8–10 ms and a large gain coefficient are easily obtained in Photorefractive ferroelectric liquid crystals.

  • real time dynamic hologram in Photorefractive ferroelectric liquid crystal with two beam coupling gain coefficient of over 800 cm 1 and response time of 8 ms
    Applied Physics Letters, 2013
    Co-Authors: Takeo Sasaki, Daisuke Miyazaki, Masashi Ikegami, Satoshi Kajikawa, Yumiko Naka
    Abstract:

    The Photorefractive Effect in photoconductive ferroelectric liquid crystals (FLCs) that contain photoconductive chiral compounds was investigated. Terthiophene compounds with chiral structure were chosen as the photoconductive chiral compounds and mixed with an achiral smectic C liquid crystal. The mixture exhibited the ferroelectric chiral smectic C phase and photoconductivity. The photorefractivity of the mixture was investigated by two-beam coupling experiment. It was found that the FLC containing the photoconductive chiral compound exhibits a large gain coefficient of over 800 cm−1 and a fast response time of 8 ms. The high Photorefractive performance was considered to be due to enhanced charge mobility.

  • Photorefractive Effect of photoconductive ferroelectric liquid crystalline mixtures composed of photoconductive chiral compounds and liquid crystal
    Journal of Materials Chemistry, 2011
    Co-Authors: Takeo Sasaki, Daisuke Miyazaki, Komei Akaike, Masashi Ikegami, Yumiko Naka
    Abstract:

    The Photorefractive Effect in photoconductive ferroelectric liquid crystals (FLCs) that contain photoconductive chiral compounds was investigated. A series of novel photoconductive chiral compounds were synthesized. Terthiophene compounds with four chiral structures were chosen as the photoconductive chiral compounds and mixed with an achiral smectic C liquid crystal. The mixtures exhibit the ferroelectric chiral smectic C phase. The photorefractivity of the mixtures was investigated by two-beam coupling experiments. It was found that the FLCs containing the photoconductive chiral compound exhibit a large gain coefficient of 110 cm−1 and a fast response time of 5 ms.

  • Photorefractive Effect of ferroelectric liquid crystals
    Chemical Record, 2006
    Co-Authors: Takeo Sasaki
    Abstract:

    This paper reviews our recent work on the Photorefractive Effect of ferroelectric liquid crystals (FLCs). The Photorefractive Effect is defined as the optical modulation of the refractive index of a medium as a result of a variety of processes. The interference of two laser beams in a Photorefractive material establishes a refractive index grating. This phenomenon enables the creation of different types of photonic applications. FLCs exhibit fast electric field response, and the orientation of the molecular axis of FLCs changes its direction according to the change in direction of the spontaneous polarization (Ps). When two laser beams interfere in a photoconductive FLC, an orientational grating is formed. The mechanism of the formation of the grating is based on the response of the Ps to the photoinduced internal electric field. The time of formation of the refractive index grating is significantly shorter in FLC materials.

  • Photorefractive Effect of Liquid Crystalline Materials
    Polymer Journal, 2005
    Co-Authors: Takeo Sasaki
    Abstract:

    This paper reviews our recent work on the Photorefractive Effect in liquid crystalline materials. The Photorefractive Effect is defined as the optical modulation of the refractive index of a medium as a result of various processes. The interference of two laser beams in a Photorefractive material establishes a refractive index grating. This phenomenon enables the creation of different types of photonic applications. Recently, the development of organic Photorefractive materials has been attracting great interest. Liquid crystalline materials are a strong candidate for practical Photorefractive materials and application. In this paper, the photorefractivity of liquid crystalline polymers and ferroelectric liquid crystals is described.

Gabriella Cipparrone - One of the best experts on this subject based on the ideXlab platform.

  • Photorefractive Effect due to a photoinduced surface charge modulation in undoped liquid crystals
    Physical Review E, 2004
    Co-Authors: P Pagliusi, Gabriella Cipparrone
    Abstract:

    We demonstrate that some peculiarities of the surface-induced Photorefractive Effect (SIPRE) in undoped nematic planar cells can be simply explained considering the electric field induced by a modulated surface-charge distribution. Polarization-dependent forced light scattering and two-beam coupling experiments indicate that the observed anisotropy of the diffraction efficiency and the energy transfer between the pump beams strongly depend on the experimental geometry. The investigation suggests that the unusual dichotomy between local and nonlocal behavior can be ascribed to a modulated longitudinal electric field component, in phase with the interference pattern, which is not accountable by the conventional photorefractivity. In a simple and general approach we demonstrate that the conceived charge distribution model for the SIPRE produces a space-charge field having two orthogonal modulated components, in-phase and $\ensuremath{\pi}∕2$ out of phase, respectively. The electric field configuration within the nematic sample gives reason for the main experimental features.

  • dynamic grating features for the surface induced Photorefractive Effect in undoped nematics
    Journal of The Optical Society of America B-optical Physics, 2004
    Co-Authors: P Pagliusi, Gabriella Cipparrone
    Abstract:

    We investigate the highly sensitive surface-induced Photorefractive gratings, observed in undoped nematic planar cells for low dc voltage (few volts) and laser intensity (few milliwatts per square centimeter). Forced-light-scattering and two-beam coupling measurements on E7 nematic samples, aligned with rubbed polyvinyl alcohol layers, verify the orientational Effect of a space-charge field and the crucial role of the polymer–liquid-crystal interface in the photoinduced processes, through a wavelength-dependent photoelectric activation. The experimental behavior supports the surface-induced Photorefractive Effect model, according to which light with the proper wavelength locally reduces the interfacial charge density, thus producing a space-charge electric field in the cell.

  • Orientational gratings in dye-doped polymer-dispersed liquid crystals induced by the Photorefractive Effect.
    Optics letters, 1998
    Co-Authors: Gabriella Cipparrone, Alfredo Mazzulla, Francesco Simoni
    Abstract:

    We report the observation of orientational gratings induced by the Photorefractive Effect in dye-doped polymer-dispersed liquid crystals. The Photorefractive origin of the grating-induction Effect is supported by the results of two-beam coupling experiments and by the possibility of erasing the grating by uniform illumination. For all the samples a stable memory Effect was observed.

Andy Yingguey Fuh - One of the best experts on this subject based on the ideXlab platform.

  • optically switchable biphotonic Photorefractive Effect in dye doped liquid crystal films
    Applied Physics Letters, 2004
    Co-Authors: Meiru Lee, Jyunruei Wang, Chiarong Lee, Andy Yingguey Fuh
    Abstract:

    This study reports the optically swichable Photorefractive (PR) Effect induced in a biphotonic grating in the presence of an applied dc voltage, in an azo-dye-doped liquid crystal (LC) film. When one green light is switched on (off), the PR grating can be turned on (off) by irradiating an interference field generated by two linearly polarized red lights. Experimental results demonstrate that such a PR Effect follows primarily from a biphotonic process, with two mechanisms—the generation of green light-induced space charges by trans–cis isomerization, and the suppression of the formation of space charges by the red light in cis–trans back isomerization. These mechanisms apply to the dark and bright fringes of the red interference field, respectively. A spatially inhomogeneous space-charge field is then established to modulate the orientation of LCs, forming the PR grating in the presence of a dc voltage. Strong coupling of the two red lights is observable and measured dynamically during the formation of th...

  • optically switchable biphotonic Photorefractive Effect in dye doped liquid crystal films
    Applied Physics Letters, 2004
    Co-Authors: M L Lee, Jyunruei Wang, Chiarong Lee, Andy Yingguey Fuh
    Abstract:

    This study reports the optically swichable Photorefractive (PR) Effect induced in a biphotonic grating in the presence of an applied dc voltage, in an azo-dye-doped liquid crystal (LC) film. When one green light is switched on (off), the PR grating can be turned on (off) by irradiating an interference field generated by two linearly polarized red lights. Experimental results demonstrate that such a PR Effect follows primarily from a biphotonic process, with two mechanisms—the generation of green light-induced space charges by trans‐cisisomerization, and the suppression of the formation of space charges by the red light in cis‐transback isomerization. These mechanisms apply to the dark and bright fringes of the red interference field, respectively. A spatially inhomogeneous space-charge field is then established to modulate the orientation of LCs, forming the PR grating in the presence of a dc voltage. Strong coupling of the two red lights is observable and measured dynamically during the formation of the PR grating in this study. © 2004 American Institute of Physics. [DOI: 10.1063/1.1836864]

Paras N Prasad - One of the best experts on this subject based on the ideXlab platform.

  • observation of the Photorefractive Effect in a hybrid organic inorganic nanocomposite
    Journal of the American Chemical Society, 1999
    Co-Authors: Jeffrey G Winiarz, Liangmin Zhang, Manjari Lal, Christopher S Friend, Paras N Prasad
    Abstract:

    We report the observation of the Photorefractive Effect in an organic−inorganic polymer composite photosensitized with nanosized cadmium sulfide particles, the surface of which is passivated utilizing p-thiocresol. The semiconductor nanoparticles are dispersed in a poly(N-vinylcarbazole) (PVK) polymer matrix that also acts as the charge-transport species. The ability of these particles to behave as the photosensitizer in a PVK matrix has been characterized through a dc photoconductivity experiment. In addition, for the Photorefractive experiments, the second-order optically nonlinear chromophore 4-nitrophenyl-l-prolinol is also doped into the PVK matrix to elicit electro-optic response. Tricresyl phosphate is used to lower the glass-transition temperature of the material, allowing for room temperature in situ poling of the sample. In addition to the electric field dependence of the degenerate four-wave mixing diffraction efficiency, the Photorefractive nature of the grating is confirmed via two-wave mixin...

  • temperature dependence studies of Photorefractive Effect in a low glass transition temperature polymer composite
    Journal of Applied Physics, 1997
    Co-Authors: Bogdan Swedek, Yiping Cui, Jeffrey G Winiarz, Ning Cheng, Jaroslaw W Zieba, Paras N Prasad
    Abstract:

    The temperature dependence of the Photorefractive Effect in a polymer composite containing poly(9-vinycarbazole), tricresyl phosphate, buckminsterfullerene, and 4-(N,N- diethylamino)-β-nitrostyrene is presented. The photoconductive, electro-optic and Photorefractive properties of the material have been studied in the temperature range of 22–61 °C. An apparent increase of electro-optic modulation with temperature and its eventual saturation is observed. This behavior is attributed to the temperature activated orientational mobility of the second-order nonlinear chromophores. The polarization anisotropy between the p- and s-polarized readouts is consistent with what would be expected on the basis of directly measured Effective electro-optic coefficients. By correlating the electro-optic value with the diffraction efficiency, the temperature dependence of the space-charge field is obtained and explained by temperature dependencies of the dark conductivity and the photoconductivity of the material.

  • Photorefractive Effect in a new organic system of doped nonlinear polymer
    Applied Physics Letters, 1992
    Co-Authors: Yiping Cui, Yue Zhang, Paras N Prasad, Jay S Schildkraut, David J Williams
    Abstract:

    We report an experimental observation of the Photorefractive Effect in a new polymeric system in which a nonlinear organic polymer was doped with a photosensitizer, borondiketonate (BDK), and a hole transport agent, tri‐p‐tolylamine (TTA). The photoconductivity and the electro‐optic Effect have been studied. The process of grating formation with the applied field is presented. A strong electric field dependence of the diffraction coefficient has been observed.

Francesco Simoni - One of the best experts on this subject based on the ideXlab platform.