Showing papers on "Organic photorefractive materials published in 2004"
TL;DR: It is shown that the group velocity of light propagating in a photorefractive material could be significantly reduced because of a steep variation of the phase-coupling coefficient with respect to the angular frequency difference between two coupling beams in a two-wave mixing process.
Abstract: We show theoretically that the group velocity of light can be slowed down by means of phase coupling in the photorefractive two-wave mixing process. It is shown that the group velocity of light propagating in a photorefractive material could be significantly reduced because of a steep variation of the phase-coupling coefficient with respect to the angular frequency difference between two coupling beams in a two-wave mixing process. The results for the case of a photorefractive Bi12SiO20 crystal are presented and discussed in detail.
38 citations
TL;DR: In this article, a theory of beam coupling in a hybrid photorefractive liquid crystal cell is developed, which consists of layers of undoped nematic liquid crystal contained within wafers of photore-fractive crystal or photoconductors.
34 citations
TL;DR: In this article, a family of photorefractive polymer composites has been developed that enable high-performance device operation at a wavelength of 975nm, which constitutes a major extension into the near-infrared spectral region for the operation of all-organic photore-fractive devices.
Abstract: A family of photorefractive polymer composites has been developed that enable high-performance device operation at a wavelength of 975nm. This constitutes a major extension into the near-infrared spectral region for the operation of all-organic photorefractive devices. Utilizing our photorefractive materials, we demonstrate large net two-beam coupling gain of more than 100cm−1, 60% diffraction efficiency in four-wave mixing experiments, and a fast response time of 33ms, at an irradiance of 1W∕cm2.
31 citations
TL;DR: In this paper, the authors identify a specific physical mechanism that leads to circular-symmetric two-dimensional photorefractive solitons, and determine the conditions for their observation.
Abstract: By means of a comparative study, we identify a specific physical mechanism that leads to circular-symmetric two-dimensional photorefractive solitons, and determine the conditions for their observation. For a given photorefractive crystal, this allows the control of the transition from an elliptical soliton-supporting regime to a round soliton-supporting one. This indicates a basic recipe to generate electro-optic devices in three-dimensional crystals compatible with single-mode fiber.
26 citations
22 citations
TL;DR: In this paper, a two-wave mixing gain in reflection grating geometry is obtained in layered organic photorefractive polymers doped with the chromophore piperidinodicyanostyrene.
Abstract: Large two-wave mixing gain in reflection grating geometry is obtained in layered organic photorefractive polymers doped with the chromophore piperidinodicyanostyrene. With an applied field of 60 V/μm and for a grating spacing of 0.205 μm, one measures a two-wave mixing gain coefficient of 104 cm−1 and a diffraction efficiency of 4.8% in 100-μm-thick samples. Our photorefractive and electrochemical investigations suggest that the excellent material performance in reflection grating geometry is associated with an increased effective number of trapping sites.
20 citations
TL;DR: In this paper, the two-color photorefractive properties in undoped as-grown near-stoichiometric lithium tantalate crystals were investigated, where a near-infrared laser and a cw ultraviolet beam were used for writing and gating, respectively.
Abstract: The two-color photorefractive properties in undoped as-grown near-stoichiometric lithium tantalate crystals were investigated, where a near-infrared laser and a cw ultraviolet beam were used for writing and gating, respectively. The key parameters in characterizing two-color photorefractive effect, light-induced absorption change, two-color sensitivity, refractive index change, readout characteristics, and dark decay were measured by changing intensities of gating and writing beams, wavelengths of gating and writing beams for the crystals with different near-stoichiometric crystal compositions, and proton concentrations. The results showed that there exists an optimal crystal composition of around 49.65% for both sensitivity and refractive index change together with moderate lifetime of small polarons. The achieved refractive index change was on the order of 10−4, and the obtained maximum sensitivity was 0.18 cm/J. The extrapolated lifetime of holograms at room temperature in the crystals without observab...
20 citations
TL;DR: In this article, photorefractive polymer composites that exhibit stable dynamic properties under continuous operation are reported. But they are based on a bis-triarylamine side-chain polymer matrix with a low ionization potential and the evolution of the response time for exposures up to 4kJ∕cm2 was studied and compared with that obtained in poly(n-vinylcarbazole) (PVK) based composites.
Abstract: We report on photorefractive polymer composites that exhibit stable dynamic properties under continuous operation. These materials are based on a bis-triarylamine side-chain polymer matrix with a low ionization potential. The evolution of the response time for exposures up to 4kJ∕cm2 was studied and compared with that obtained in poly(n-vinylcarbazole) (PVK) based composites. In the composites, operational stability is combined with video-rate compatible dynamics, large dynamic range at moderate fields, and long shelf lifetimes.
18 citations
TL;DR: In this paper, the ultraviolet-light-induced defect centers O− responsible for the broadband absorption changes act as shallow centers in UV-lightgating two-color holography.
Abstract: We investigate the ultraviolet- (UV-) light-induced two-color photorefractivity in a near-stoichiometric LiNbO3 crystal doped with Mg above the damage-resistant threshold concentration. Measurements of holographic recording and optical fixing dynamics with a 365-nm gating beam show that complementary shallow and deep gratings are formed during recording and that at least four defect centers are involved in the two-color holographic recording process. It is confirmed that UV-light-induced defect centers O− responsible for the broadband absorption changes act as shallow centers in UV-light-gating two-color holography. These findings indicate that the physical mechanism of the UV-light-gating two-color photorefractive effect in the crystal is essentially different from that of the recently reported two-color photorefractive effect in Mg-doped near-stoichiometric LiNbO3 with a 488-nm gating beam [Appl. Opt. 41, 4891 (2002)].
13 citations
TL;DR: In this article, the photorefractive space-charge field in a chiral smectic C mesophase was measured and a model connecting the induced refractive index modulation with the electric fields within the medium was proposed.
Abstract: We report on the measurement of the photorefractive space-charge field in a chiral smectic C mesophase. The liquid crystal is intrinsically photoconducting and undoped. The space-charge field amplitude, obtained from a model connecting the induced refractive index modulation with the electric fields within the medium, is only 1% of the applied field. Nonetheless, high refractive index modulations Δn∼10−3 can be obtained because of the high spontaneous birefringence of the mesophase. The use of the standard models for inorganic crystalline photorefractive materials would have given a space-charge field amplitude two orders of magnitude higher.
10 citations
Patent•
20 Dec 2004TL;DR: In this article, an alkali alumino-silicate Na-F-containing glass material and a method of making the glass material capable of being made photosensitive and thus formed into optical elements at wavelengths ranging between about 240 to 350 nm, and more particularly at the standard 248nm wavelength of excimer lasers.
Abstract: The present invention provides an alkali alumino-silicate Na-F-containing glass material and a method of making the alkali alumino-silicate Na-F-containing glass material, with the glass material capable of being made photosensitive and thus formed into optical elements at wavelengths ranging between about 240 to 350 nm, and more particularly at the standard 248nm wavelength of excimer lasers. Also disclosed is optical element wherein a refractive index pattern formed in the alumino-silicate Na-F containing glass material, the refractive index pattern including regions of high refractive index and regions of low refractive index, the difference between the refractive indices of the high refractive index regions and the low refractive index regions being at least 4x10-5 at a wavelength of 633 nm.
TL;DR: In this paper, a photorefractive sample in which a chromophore (P-IP-DC) was dispersed showed a high diffraction efficiency of 85% at an external field of 28 V/μm.
Abstract: Optically controlled spatial light modulator was demonstrated as application of photorefractive polymeric material. Photorefractive composites based on photoconducting carbazole-substituted polysiloxane matrix (PSX-Cz) show an excellent stability against phase separation, compared to poly(N-vinyl carbazole) based composite. 2-[3-[(E)-2-(piperidino)-1-ethenyl]-5,5-dimethyl-2-cyclohexenyliden] malononitrile (P-IP-DC) has large dipole moment and large polarizability anisotropy. A photorefractive sample in which a chromophore (P-IP-DC) was dispersed showed a high diffraction efficiency of 85% at an external field of 28 V/μm. Application of photorefractive material for the optically controlled spatial light modulator which can convert incoherent optical image imposed in Xe-lamp light into coherent image in He–Ne laser wavelength is demonstrated using this composite.
TL;DR: In this article, the orientational photorefractive properties of mesogenic composites were investigated by means of two-beam coupling and degenerate four-wave mixing, and large index modulation of over 0.01 was obtained.
Abstract: The orientational photorefractive properties of photorefractive mesogenic composites have been investigated by means of two-beam coupling and degenerate four-wave mixing. Photorefractive mesogenic composites, consisting of low molar mass liquid crystals, polymer, and photoconductive sensitizer, constitute novel organic materials possessing high performance photoreractivity. The refractive index change was estimated on the basis of the theory of two-beam coupling and four-wave mixing, and large index modulation of over 0.01 was obtained.
Journal Article•
TL;DR: In this article, the optical transmission spectra of double-doped LINbO3 was studied in a series of different densities of different dopants, different concentrations of dopants and different as-grown samples (or reduced or oxidized).
Abstract: Photorefractive holographic storage and optical transmission spectra properties were studied in a series of double-doped LINbO3 crystals including different dopants, different concentrations of dopants, and different as-grown samples (or reduced or oxidized) . The experimental results show that the optical transmission spectra range is smaller in the high concentrations doped LiNbO3 crystals. The larger optical transmission spectra range can be obtained in the oxidized samples. And the greater gain of photorefractive effect two-wave mixing can be obtained in reduced samples. It is difficult to maintain the high gain of photorefractive effect two-wave mixing and the top-quality photorefractive holographic storage simultaneously.
TL;DR: In this article, the effect of a trapping molecule on two closely related monolithic organic photorefractive (PR) materials was described, and it was found that the trapping molecule C affects the PR performances differently in two materials made from either A or B, although the two molecules have similar chemical structures.
Abstract: A peculiar effect of a trapping molecule on two closely related monolithic organic photorefractive (PR) materials was described. It was found that the trapping molecule C affects the PR performances differently in two materials made from either A or B, although the two molecules have similar chemical structures. Detailed studies on the charge mobility with the time-of-flight technique and activation energies for charge transport revealed that the trapping molecule C plays the role of electron trapper in material A and bipolar trapping center for both hole and electron in material B.
TL;DR: Using circular polarization of the input HeNe laser beam, it is succeeded to create a stable self-focused, asymmetric light-beam over several hours, where a transient symmetric state is observed.
Abstract: We present experimental results on the self-focusing of light beams in a photorefractive, optically active Bi12TiO20 crystal. Using circular polarization of the input HeNe laser beam we succeeded to create a stable self-focused, asymmetric light-beam over several hours. Depending on external parameters, like the external electric field and the intensity ratio, a transient symmetric state is observed.
26 Oct 2004
TL;DR: In this article, an optical novelty filter based on the two-beam coupling effect in photorefractive polymers was proposed, which was optimized for response time and gain by changing the ionization potential and polarizability of various components.
Abstract: We have demonstrated an optical novelty filter based on the two-beam coupling effect in photorefractive polymers. The photorefractive polymer composition was optimized for response time and two-beam coupling gain by changing the ionization potential and polarizability of various components. In this study, a photorefractive polymer composition was simultaneously optimized for response time and gain, and employed as a key element in a two-beam coupling novelty filter with a high contrast ratio and a limiting frequency of 14Hz, considerably higher than any previously reported in a two-beam coupling photorefractive novelty filter.
TL;DR: In this paper, edge enhancement, a type of intensity filtering of two-dimensional optical image, was demonstrated using dye-doped photorefractive liquid crystal films, and the expected images were calculated using four wave mixing geometries.
Abstract: Edge enhancement, a type of intensity filtering of two-dimensional optical image, was demonstrated using dye-doped photorefractive liquid crystal films. We calculate the expected images using four wave mixing geometries, which show good agreement with the image that we experimentally observed using dye-doped liquid crystal as the photorefractive materials.
TL;DR: Theoretical analysis of photorefractivity in dye-doped nematic liquid crystal film is discussed in this article, where analytical solutions of refractive index distribution and the first order diffraction efficiency are presented.
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.
15 Oct 2004
TL;DR: In this article, the effect of micro-domains in polymer films on the photorefractive effect was investigated using a four-wave mixing experiment and it was shown that micro-domain structures in the polymers with the hydrogen-bonding moieties were more effective than those without them.
Abstract: The effect of the introduction of micro-domains in polymer films on the photorefractive effect was investigated. The photorefractivity of side-chain liquid crystalline polymers that possess a hydrogen-bonding moiety was examined using a four-wave mixing experiment. The photorefractivity was compared to that of a polymer which has no hydrogen-bonding moiety. A significant difference was found in the photorefractivity between hydrogen-bonding polymers and non-hydrogen-bonding polymers. This difference was likely due to the presence of micro-domain structures in the polymers with the hydrogen-bonding moieties.
26 Oct 2004
TL;DR: In this article, a tetraphenyldiaminobiphenyl (TPD) based polymer composites were developed for operation wavelengths up to 1 micron, where a new dye with enhanced near-infrared absorption was employed to extend the sensitivity into this long wavelength range.
Abstract: We describe the material characteristics and photorefractive properties of novel tetraphenyldiaminobiphenyl (TPD) based polymer composites that were developed for operation wavelengths up to 1 micron. With an optimized composite, we demonstrated more than 50% external diffraction efficiency coupled with a fast response time of about 35 ms at 980 nm. In addition to this high performing composite, we have developed a composite with high two beam coupling gain (300 cm -1 ). To accomplish these attractive photorefractive properties in the near-infrared, we explored the chemical flexibility of the guest-host approach. We employed a new dye with enhanced near-infrared absorption to extend the sensitivity into this long wavelength range. Styrene-based chromophores were utilized to enable high refractive index modulation. We explored ellipsometry as well as photo-conductivity measurements to optimize the composition of the composites. In addition to the composites that contain a single chromophore species, we also analyzed samples prepared with a mixture of chromophores. Our studies reveal the potential of this new polymer-composite family to extend the operation wavelength of the photorefractive materials to even longer wavelengths. Attractive photorefractive properties coupled with long wavelength sensitivity make these materials potential candidates for imaging and communication applications. Keywords: photorefractive polymers, holographic materials, nonlinear optical materials, charge transport matrix, TPD
02 Aug 2004
TL;DR: In this paper, the photorefractivity at 1.55 µm in a polymer composite was demonstrated using twophoton absorption, and large diffraction efficiency and holographic reconstruction of distorted images utilizing thin-film devices made of this polymer.
Abstract: Photorefractivity at 1.55 µm in a polymer composite is demonstrated using twophoton absorption. We show large diffraction efficiency and perform holographic reconstruction of distorted images utilizing thin-film devices made of this polymer.
TL;DR: In this paper, the photorefractive effect of a series of low-molecular-weight ferroelectric liquid crystals (FLCs) doped with photoconductive compounds was investigated using two-beam coupling experiments.
Abstract: The photorefractive effect of a series of low-molecular-weight ferroelectric liquid crystals (FLCs) doped with photoconductive compounds was investigated using two-beam coupling experiments. Asymmetric energy exchange was observed only in the ferroelectric phase, and the refractive index formation time was found to be ∼30 ms, which is faster than that of nematic photorefractive LCs. These results indicate that the mechanism of the photorefractive effect in FLCs is different from that in nematic LCs. The photorefractivity of a photoconductive polymer and FLC mixture was also investigated, and the effects of temperature, the strength of the applied electric field and spontaneous polarization on the diffraction efficiency were examined.