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A kind of citrus fruit with special flavor, Citrus sudachi harvested in Japan, are exported to various countries. However, the Citrus sudachi needs to be sterilized using aqueous solution of sodium hypochlorite because there is a possibility of the adhesion of citrus bacterial canker (CBC) which is not found in Europe. Due to the sterilization with time-consuming work, a more effective decontamination technique is required. A decontamination method using ultraviolet (UV) light irradiation is thus anticipated. Especially, the use of light emitting diodes (LEDs) wi UV light has many advantages in terms of energy consumption, lifetime, and compactness； although an appropriate method is yet to be established. In this study, we evaluate the fundamental effectiveness of UV-LED decontamination on the basis of the bactericidal ability on CBC in petri dishes, using six kinds of UV-LEDs (265, 280, 285, 300, 310, and 365 nm) . For each irradiation, the resultant bactericidal abilities (BAs) were evaluated precisely taking into account the differences in their optical absorptions. In addition, BAs per unit photon number were also estimated, as a fundamental wavelength-dependence of BA. As a result, the effectiveness of UV-LED irradiation with relatively short wavelengths was demonstrated clearly.

This paper proposed a board-mounted ultrasonic variable-focus liquid crystal (LC) lens. The lens controls the focus using the acoustic radiation force generated by the resonant flexural vibration mode. The LC lens was fixed to an aluminum substrate with a hole whose aperture corresponded to the inner diameter of the transducer. The part of the LC lens attached to the substrates functioned as a fixed condition, and the flexural vibration mode was successfully generated. The fixed lens exhibited a gradual focal change with current, confirming that fixing the condition affected the rate of focal change.

The orientation angles of liquid crystal (LC) molecules were measured during ultrasound vibrations. Light transmitted through a fabricated LC lens was analyzed via the crossed Nicol condition and a crystal rotation method. The LC orientation angle was estimated with a theoretical model, and its distribution in the lens was determined. There was a strong correlation between the molecular angles and ultrasonic vibrational distributions, indicating that the angle was changed by the acoustic radiation force. The maximum tilt angle was 12° for a 50 V peak-to-peak input.

A method to improve the performance of an ultrasound liquid crystal lens is proposed. A double-layer-based lens model tailored based on the liquid crystal’s physical properties, e.g., its dielectric anisotropy and elastic constants, is presented as an alternative method to improve the lens’s optical performance while forming weak anchoring surfaces for nematic liquid crystals, thus promoting easier reorientation of the liquid crystal molecules. The lens configuration was simulated by finite-element analysis using Ansys software. The lens’s physical and optical characteristics were evaluated via comparison using two different liquid crystal materials: 5CB and RDP-85475. The birefringence distribution within the liquid crystal layer was investigated under ultrasound excitation, and the molecular angles of inclination were estimated. A higher birefringence distribution, greater molecular inclination, and a longer focal length were obtained for the double-layered liquid crystal lens using the 5CB material.

In this paper, we propose a novel approach to fabricate fluidic chips. The method utilizes molecular cross-diffusion, induced by photopolymerization under ultraviolet (UV) irradiation in a channel pattern, to form the channel structures. During channel structure formation, the photopolymer layer still contains many uncured molecules. Subsequently, a top substrate is attached to the channel structure under adequate pressure, and the entire chip is homogenously irradiated by UV light. Immediately thereafter, a sufficiently sealed fluidic chip is formed. Using this fabrication process, the channel pattern of a chip can be designed quickly by a computer as binary images, and practical chips can be produced on demand at a benchtop, instead of awaiting production in specialized factories.

The effect of the liquid crystal (LC) layer thickness on the optical characteristics of an ultrasound LC lens was explored. Three LC lenses with differing LC layer thicknesses (100, 200, and 300 μm) were fabricated, and the optical focal lengths were measured by an optical microscope with a varying driving voltage. For the lens with a 200 μm thick LC layer, a larger change in the focal length was observed for a smaller driving voltage compared with that of the other two lenses, indicating that the LC layer thickness is appropriate for a variable-focus lens.

In the previous study, we evaluated the effectiveness of an orthogonal polarizer array to suppress the inter-pixel cross talk with respect to the page data recording in holographic memory (Nobukawa et al. in Opt Express 25:22425, 2017). The reconstruction quality was improved by the use of the orthogonal polarizer array applied for the signal beam, based on the reduction of inter-pixel cross talk. In the present study, we also employed a similar polarizer array for the detection of a reconstructed image. Simultaneously, some phase shift masks and various apertures restricting the recording spot were also applied for the holographic recording. As a result, we found that the areal density and reconstruction quality were improved significantly based on the suppression of inter-pixel cross talk and reduction of recording spot size. These findings can be used for the realization of practical high-density holographic memory.

The formation of submicron polystyrene (PS) particles based on dewetting process during spin-coating was investigated. The surface morphologies on glass substrates were analyzed. The formation of particles was achieved using PS with relatively high molecular weight (Mw ≥ 3250). In addition, it was observed that the particle formation proceeded through sequential morphological changes in the order of initial wet thin film, secondary spinodal-decomposed structures, and eventual dewetted particles. One of the fabricated samples exhibited obvious optical resonance in the visible region based on the relationship between particle dimeters and optical wavelengths in the visible region. The optical resonance strongly depended on the ambient refractive index, which can be used for optical sensor-chips. Finally, a multi-functional biosensor-chip was demonstrated to detect glucose in water solutions.

In this paper, we evaluate a novel flaw-detection technique for metallic surfaces based on the use of phase-type blazed gratings. Transparent blazed gratings were prepared by the soft nanoi...

A random phase mask is often used for Fourier transform holography to improve its recording and reconstruction characteristics. However, a conventional random phase pattern has the disadvantage of expanding the recording spot, which is caused by the high-resolution phase modulation. Previously, we proposed a random phase pattern that makes the recording spot narrower than the conventional one with maintaining a moderate reconstruction quality. In the present study, we apply the proposed random phase pattern to computer-generated binary holograms and evaluate both the hologram distribution and reconstruction quality in terms of practical holographic memory systems. The results confirm the effectiveness of the random phase in the reconstruction for an elementary data pattern.

New technologies for adaptive optics are becoming increasingly important for miniature devices such as cell-phone cameras. In particular, motion-free autofocusing and optical image stabilization require sophisticated approaches for alternative lens architectures, materials, and processing to replace multiple solid elements. We discuss a new method, to the best of our knowledge, that provides image stabilization via an annular piezoelectric ceramic that uses ultrasound to drive a liquid crystal layer sandwiched between two circular glass substrates. The piezoelectric ceramic is divided into four quadrants that are independently driven with sinusoidal voltages at the resonant frequency of the lens. The technique is based on ultrasound vibrations with a suitable driving scheme. The lens configuration was modeled via finite-element analysis. Various combinations of the four-channel ultrasound transducer can be used to define the focal point of the liquid crystal lens. Clear optical images could be obtained with the lens. By using two-dimensional fast Fourier transforms, the focal point position was defined and shifted in the radial direction.

In this paper, we propose a ring-type grating in which grating vectors formed by periodic molecular alignments are superimposed radially. Depending on incident polarization states, the anisotropic gratings generate polarization dependencies for the ring-like first order diffraction. To determine the polarization states of incident light for both single and multi-wavelengths, we attempted to extract the optical intensity distribution on the ring-like diffraction from each single-shot diffraction image. In addition, a system that enables the detection of spatial modulation of optical birefringence is proposed. Finally, we concluded that the optical intensity distribution on the circumference of the ring-like diffraction has sufficient potential to be available.

エラストマーの一種であるポリジメチルシロキサンのようなシリコーン樹脂は多くの製品に使用されている。シリコーン粘着剤もまた多くのテープやラベルに用いられている。本研究では、市販のシリコーン粘着剤の各種基板に対する接着特性を90°剥離試験を用いて調査した。結果として、金属系基板、プラスチック系基板、ケイ素系基板の中で、その種類ごとに、異なる接着特性を示した。これらの知見は、異種材料接合などに有効となると考えられる。, A kind of elastic polymer, silicone polymers like a polydimethylsiloxane is used for many products exceptionally. Pressure-sensitive silicone adhesives are also used for many kinds of tapes or labels. In this study, we investigated the adhesion characteristics of a commercial product of silicone pressure-sensitive adhesive tape to various substrates based on a method of 90 °-peel test. As a result, the adhesion characteristics were dependent on the materials of the substrates among metals, plastics, and silicone series. This find would be useful for joining different kinds of materials.

A high-density array of barnacle-like porous structures was fabricated using monolayers of polystyrene spheres and various types of poly(vinyl alcohol). We first prepared the polystyrene sphere monolayer as a close-packed hexagonal array on a glass substrate. The monolayer was then etched using a plasma treatment to isolate each sphere. Next, we spin-coated the isolated spheres with a water solution of poly(vinyl alcohol). After drying, we applied a second short plasma treatment to the substrate before immersing it in a toluene bath, which promoted opening formation due to polystyrene swelling. As a result, a high-density array of barnacle-like porous structures was homogenously formed on the substrate. These porous structures are expected to be used for various applications including functional coatings, protective cell cultures, and sensor chips.

In our previous study, we developed an array of unique porous structures (an array of barnacle-like porous structures) to apply to biosensing chips. The porous structure was formed by an internal swelling phenomenon of a polystyrene colloidal particle monolayer, which was surrounded by a poly(vinyl alcohol) layer, for the duration of the monolayer's immersion in a toluene bath. Barnacle-like porous structures were formed when polystyrene particles that had rapidly swelled broke the outer layer around the top of the particles. However, after the surface was coated with a thin Ag layer, the porous structure showed a relatively broad extinction spectrum that was undesirable for sensing chips based on both surface plasmon extinction and grating coupling. In this paper, we propose an approach to obtain relatively sharp extinction spectra based on the decimation of the spatial frequencies of the porous structures. This study also investigates formation properties in more detail to control the structural features of the resultant porous structures. A relatively sharp peak in the extinction spectrum was ultimately obtained.

Sensitive and functional biosensor chips are required to detect various molecules or substances. We have developed a fabrication process for an unique porous structure which was fabricated from poly(vinyl alcohol)-coated polystyrene template. In this study, the formation mechanism such porous structure is investigated in detail.

Fresnel lens has a distinct wavelength dispersion for the focal lengths. This characteristic allows to apply Fresnel lens to a wavelength dispersion element for spectrometers. We have simulated the focusing characteristics of an advanced Fresnel lens which has a feature of eccentric modification to realizing a compact spectrometer.

Low-temperature radical polymerization of achiral N-allyl-N-tert-butylacrylamide (AltBAAm) was conducted in toluene in the presence of chiral tartrates, such as diethyl l -tartrate (L-EtTar) and di-n-butyl l -tartrate. The 1H NMR spectra of the polymers obtained indicated progress of cyclopolymerization at low temperatures such as −80 °C. Optical properties of the poly(AltBAAm)s examined by optical rotation and circular dichroism measurements indicated asymmetric induction in the cyclopolymerization of achiral AltBAAm. For example, addition of L-EtTar at −80 °C provided the polymer with specific rotation of −4.8°. The tert-butyl groups of poly(AltBAAm)s were removed by treatment with CF3SO3H, transforming into poly(N-allylacrylamide)s [poly(AlAAm)s]. Then, stereochemistry in the stereorepeating unit was investigated by comparing 1H NMR signals of the poly(AlAAm)s with those of model compounds, cis- and trans-3-ethyl-4-methyl-2-pyrrolidones. Taking the negative specific rotation values of the poly(AltBAAm)s obtained with L-tartrates into account, it was revealed that (3S,4S)-trans-unit was predominantly formed through the hydrogen-bond-assisted complex formation of AltBAAm with L-tartrates.

Organic-inorganic hybrid films are fabricated by applying a sol-gel method using perhydropolysilazane (PHPS), which are then applied on the active layers of quadruple-layer structure organic light-emitting diodes (OLEDs). All organic layers are fabricated using wet-process. In the quadruple-layer OLEDs consisting of the active layer without the sol-gel reaction, electroluminescence (EL) emissions from the active layer is not observed. This is because the electron-transporting layer and the adjacent active layer are mixed. However, if the sol-gel reaction is performed the EL emissions from the active layer are clearly observed. This is because the active layer is not destroyed due to its insolubility.

We fabricated aluminum (Al) and gallium (Ga) co-doped ZnO films by wet-process and evaluated their sheet resistances and transmission spectra. It was found that the sheet resistance becomes minimum when the content ratios of Al and Ga are 0.02 at the annealing temperature of 550 degree. Moreover, we found that the sheet resistance can be improved by performing the spin-coating and annealing twice. In this case, the transmission probability in the visible light regime is more than 90%. This result is a simple method to fabricate fine transparence conductive ZnO films.

A method to estimate orientation direction of liquid crystal molecules three-dimensionally under ultrasound excitation was proposed and the relationship between the ultrasound vibration and the molecular orientation was discussed. Our group have reported a technique to control orientation direction of liquid crystal molecules using ultrasound vibration which could be applied to an optical variable-focus liquid crystal lens. The lens consisted of a liquid crystal layer sandwiched by two glass circular discs and a piezoelectric ring. Ultrasound vibration induces change in the refractive index of the lens, enabling the variable-focus function. The three-dimensional orientation direction of the liquid crystal molecules in the lens was predicted from the transmitted light distributions under the crossed Nicol conditions. The liquid crystal molecules were inclined from vertical alignment by the ultrasound vibration, and larger ultrasound vibration gave larger inclination of the molecules. There was a strong correlation between the distributions of ultrasound vibration and the liquid crystal molecular orientation; the molecular orientation was changed remarkably between the antinodal and nodal parts of the ultrasound flexural vibration on the glass plate and the molecules aligned towards the antinode.

As a potential means of measuring birefringence distribution, we analyzed the interference fringes based on three circularly polarized beams: a right-handed signal beam, a left-handed reference beam, and a right-handed reference beam. All beams were crossed at the same angle on the interfering plane, creating a two-dimensional interference fringe with three grating vectors. We proposed that by analyzing the interference fringes, we can measure the anisotropic phase shift in the signal beam. The obtained features of the anisotropic phase shift can be extended to the measurement of two-dimensional birefringence distributions without rotational manipulations of the objectives or polarizers. The fringes were generated by monolithic gratings, which can generate three-beam interfering fields precisely and easily. Finally, we confirmed the feasibility of a birefringence measurement system without any rotational manipulations of optics.

Nematic liquid crystal is widely used in optical devices such as liquid crystal displays. The optical characteristics of liquid crystal devices (ex, birefringence) can be controlled by applying an electric field because the liquid crystal molecules have electric dipoles. Although indium tin oxide (ITO) is generally employed as the transparent electrode material, ITO needs the rare metal indium and has problems of low electric conductivity and transparency. Our group has proposed a novel control technique of liquid crystal molecular orientation using ultrasound vibration without using ITO [1]. In this report, an optical variable-focus liquid crystal lens using ultrasound was discussed.

Submicron-size of colloidal spheres itself and their self-assembled structures are useful basis for obtaining various functional structures. Up to now, we have succeeded to fabricate several unique structures that are expected to be applied to various components of a specific optical device, or the substrate for material- and/or bio-science research purpose. Facile fabrication procedures and obtained structures for an inverse opal structure, a binary colloidal structure, an alternating photonic crystal and glass structure, and an anisotropic hemispherical structure are introduced. Their optical functions are also described.

A first-order beam diffracted by periodic arrays of GMR structures consisting of Pt/Co free layers having perpendicular magnetization without a top electrode is investigated. Linear and two-dimensional arrays of various shapes having sizes of 10–50 μm and periods of 20–100 μm embedded in SiO 2 are fabricated. The angles of the plane of polarization for first or (1,0) diffraction spots at a wavelength of 633 nm are measured to be approximately 0.5° for all samples. The polarization angles for one- and two-dimensional arrays of magnetic patterns are studied theoretically by assuming that the structures have sinusoidal magnetic distributions. They are found to depend on the Kerr rotation angle of the Pt/Co multilayer and on the difference in reflectance between the Pt/Co and SiO 2 , but they are independent of the periodicities, sizes, and shapes of the patterns. On the other hand, the diffraction efficiencies due to the magneto-optical effect depend on the reflectance and Kerr rotation angles of the magnetic materials. The diffraction efficiency of the component arising from the magneto-optical effect is discussed.

Random phase masks are important technical elements for realizing holographic memory systems that enable high density recording. However, the broadly distributed Fourier spectrum often presents a problem because wide recording spots result in reduced total storage capacity for a recording medium. In the present study, we propose modified random phase masks with phase modulation elements exhibiting Gaussian profiles to suppress the spread of the recording spot and keep it in a narrow area, based on the reduction of the high-frequency components in a random phase pattern. We confirm the effectiveness of the proposed random phase mask using simulations of a computer-generated binary hologram. However, issues still remain in terms of the fabrication of random phase masks with Gaussian profiles. Therefore, we evaluate the feasibility of fabricating the proposed random phase mask using molecular diffusion under photopolymerization. The results confirm the feasibility of this approach over a relatively wide area for actual fabrication.

We studied the polarization state in an apertureless scanning near-field microscopy (a-SNOM) operating in reflection mode by using three-dimensional Finite-difference Time-domain (FDTD) method. As a result, the electric field around tip apex in the near-field region enhanced four times stronger than the incident light for ppolarization when the tip-sample separation was 10 nm. We find that the p- and s-polarization state is maintained for the scattered light when the probe is perpendicular to the sample. When the probe is not perpendicular to the sample, the polarization state of scattered light will rotate an angle that equals to the inclination angle of probe with p-polarization illumination. On the other hand, the polarization state will not rotate with s-polarization illumination.

In this work, we report on a dichroic reflection phenomenon in the specular direction. The reflective medium is an Au-coated anisotropic hemispherical structure (AuAHeS), composed of a polymer material, which is fabricated via a replication process based on a polystyrene (PS) spherical particle array monolayer. Structural anisotropy is provided artificially by stretching the silicone rubber mold used in the replication process. Depending on the anisotropy of the resulting structure, the absorbance spectra are significantly altered for incident light that is polarized either parallel or perpendicular to the stretching direction. Based on the optical characteristics of the structures observed in the present study, the generation of unique devices for optical, photonic, and bio-photonic applications is expected to be possible.

Anisotropic diffractive gratings formed by birefringent molecular alignment are fabricated by a holographic technique using a photo-cross-linkable liquid crystalline copolymer (PLCCP). Depending on the exposure energy used for holographic recording, bright or dark regions of the interference fringe can be chosen for the molecular-aligned region, analogous to positive- and negative-type photoresist processing in photolithography. In conjunction with simultaneously generated surface relief gratings, the anisotropic refractive index modulation inherent in the PLCCP film exhibits different diffraction properties depending on the incident beam polarization. The anisotropic refractive index grating profiles are quantitatively presented for two cases determined by the exposure energy, based on the Fourier analysis of diffractive optics. The selection of different grating formations selected by varying only the exposure energy could provide a strategy for the fabrication of functionalized diffractive optical elements.

Self-assembling of binary colloidal crystals (bCCs) consisting of spherical particles with different diameters has been used for monolayer fabrication in glass cells. The procedure involves two crystallization steps. Upon crystallization of a colloidal suspension containing large spheres, a monolayer is formed on the bottom substrate of the cell. Then, a colloidal suspension containing small spheres, which assemble in the interstitial parts between the large spheres, is injected into the cell. The resulting bCC monolayers are characterized using scanning electron microscopy (SEM) and reflection spectroscopy. Reflection spectra reflect the bCC structure and forbidden bands corresponding to the grating constant of the second colloidal crystal. The structure and optical properties of the bCC monolayer can be specified depending on the ratio of the diameters of the spheres. The proposed process for bCC monolayer fabrication is extremely simple, and therefore ideal for practical uses.

Photocontrol of molecular alignment is an exceptionally-intelligent and useful strategy. It enables us to control optical coefficients, peripheral molecular alignments, surface relief structure, and actuation of substances by means of photoirradiation. Azobenzene-containing polymers and functionalized liquid crystalline polymers are well-known photocontrollable materials. In this paper, we introduce recent applications of these materials in the fields of mechanics, self-organized structuring, mass transport, optics, and photonics. The concepts in each application are explained based on the mechanisms of photocontrol. The interesting natures of the photocontrollable materials and the conceptual applications will stimulate novel ideas for future research and development in this field.

A new asymmetric polarization holography was conducted to form a blazed surface relief (SR) structure in a polymethacrylate film comprised of 4-methoxyazobenzene side groups using asymmetrically controlled polarized 325 nm He–Cd laser beams. Asymmetrical molecular migration, which generated the blazed SR structure, was achieved by adjusting the influence of both the intensity and polarization distributions of the two beams on molecular migration.

Nematic liquid crystal is widely used in optical devices such as liquid crystal displays and controlled by electric fields through the liquid crystal layer. Our group has proposed a control technique of liquid crystal molecular orientation using ultrasound vibration without indium tin oxide electrodes [1]. In this study, using ultrasound and nematic liquid crystal, we realized a variable focus liquid crystal lens. The liquid crystal lens has no transparent electrodes and consists of a simple structure; a nematic liquid crystal layer with a thickness of 50 μm is formed between two circular grass plates. An annular PZT ultrasonic transducer was bonded on the glass plate. By exciting the transducer at the resonance frequencies (28 kHz), the flexural vibration modes were generated. The acoustic radiation force from the vibration changed the molecular orientation of the liquid crystals, which induced the distribution of the execution refractive indices. The liquid crystal layer then worked as a lens. The focal...

Surface relief (SR) gratings with a molecularly oriented structure and pure polarization hologram were fabricated on a photo-cross-linkable liquid crystalline copolymer using a 325-nm laser with various two-beam polarization modes. For intensity holography, the polarization information from the two beams simultaneously provided the molecular motion and molecular reorientation; the SR height reached up to 186 nm and the concave area revealed a molecular reorientation when the exposing beams were linearly polarized. In contrast, SR formation was negligible for polarization holography when molecular reorientation due to the polarization modulation was observed. The resulting polarization gratings changed the polarization properties of the diffraction beams, and their diffraction efficiency was reached 24%, which agreed with theoretical expectations.

A series of π-conjugated alternating copolymers consisting of Th-ITN-Th and p-C 6 H 2 (OR) 2 units were synthesized. XRD indicated that the copolymers assume an interdigitation packing mode, and UV-Vis spectra revealed a strong tendency for self-assembly. Upon molecular assembly of the copolymer, the UV-Vis absorption shifted by about 100 nm to a longer wavelength from that of the single molecule. The copolymers underwent electrochemical oxidation (or p-doping) and reduction (or n-doping) at 0.2 and -2.0 V versus Ag + /Ag, respectively. A p-doped copolymer film showed an electrical conductivity of 182 S · cm -1 , and the temperature dependence of electrical conductivity was measured. The copolymer showed piezochromism and served as a p-channel material for a field-effect transistor.

A new photo-cross-linkable liquid crystalline polymer (PLCP) comprised 4-methoxycinnamoyloxy groups connected with a bistolane side group was synthesized to investigate thermally enhanced photoinduced molecular reorientation of a thin film with linearly polarized (LP) 365 nm light exposure. Due to the axis-selective photoreaction of the cinnamate groups followed by the thermally induced self-organization, large molecular reorientation parallel to the polarization of LPUV light ( S > 0.6) and large birefringence at the non-resonance region (Δ n = 0.34 at 632.8 nm) were obtained. The obtained Δ n value is the largest among transparent PLCPs in the visible region. The influence of the degree of photoreaction and the annealing temperature on the thermally enhanced molecular reorientation behavior was explored in detail. Finally, for an application of thin optical devices using the PLCP films, pure polarization holographic gratings with large birefringence, which showed periodic molecularly oriented structure, were fabricated using a 325 nm He–Cd laser in various polarization modes and characterized their optical properties.

A variable-focus lens using a combination of liquid crystals and ultrasound is discussed. The lens uses a technique based on ultrasound vibration to control the molecular orientation of the liquid crystal. The lens structure is simple, with no mechanical moving parts and no transparent electrodes, which is helpful for device downsizing; the structure consists of a liquid crystal layer sandwiched between two glass substrates with a piezoelectric ring. The tens-of-kHz ultrasonic resonance flexural vibration used to excite the lens generates an acoustic radiation force on the liquid crystal layer to induce changes in the molecular orientation of the liquid crystal. The orientations of the liquid crystal molecules and the optical characteristics of the lens were investigated under ultrasound excitation. Clear optical images were observed through the lens, and the focal point could be controlled using the input voltage to the piezoelectric ring to give the lens its variable-focus action.

Effects of recording wavelength on the recently proposed (Sasaki, 2008) three-dimensional vector holograms, in which the optical anisotropy is three-dimensionally modulated, are presented experimentally and theoretically. The polarization states of the interference light are three-dimensionally modulated due to both the polarization interference and optical anisotropy in the recording medium. These spatial distributions of the polarization states and the resulting diffraction properties in the three-dimensional vector holograms are strongly dependent on the recording wavelength. Theoretical consideration based on the finite-difference time-domain (FDTD) method reveals the mechanism of the optical characteristics of the three-dimensional vector holograms recorded by various kinds of light sources with different wavelengths.

New photo-cross-linkable liquid crystalline polymethacrylate with 4-methoxybistolane side groups was synthesized and its thermally enhanced photoinduced molecular reorientation behavior was investigated using a linearly polarized (LP) UV light. Since the bistolane mesogenic side groups were axis-selectively photoreacted under irradiating with LPUV light, annealing procedure generated the thermally enhanced molecular reorientation parallel to the polarization (E) of LP-365 nm light. The axis-selectively photoreacted bistolane moieties acted as the photo-cross-linked anchor to reorient non-photoreacted side groups along them, which direction was parallel to E. The maximum generated in-plane order parameter and birefringence were 0.43 and 0.18, respectively. The influences of degree of the photoreaction and the annealing temperature on the molecular reorientation behavior were investigated in detail. Furthermore, polarization holography using 325 nm He-Cd laser was carried out to fabricate pure polarization gratings with various polarization of the light source.

Self-assembly of polythiophenes with –C≡CR (R = alkyl, phenyl, etc.) side chains has been investigated. Seven new polymers consisting of head-to-head and tail-to-tail 2,2′-bithiophenes with –C≡CR s...

Light wave propagation in thick polarization gratings has been studied using the finite-difference time-domain (FDTD) method. The diffraction properties of the polarization Bragg gratings were strongly dependent on both the polarization state and incident angle of the probe beam. These characteristics were well explained by the FDTD calculation and the subsequent Fourier transformation. The FDTD calculation also revealed the light electric field near and/or in the polarization Bragg gratings.

We have developed holographic gratings that enable the asymmetric polarization conversion between ±1-order diffraction beams. The holographic gratings are formed by polarization holography in a poly[(methyl methacrylate)-co-(disperse yellow 7 methacrylate)] film and show both anisotropic phase and surface modulations. For an azobenzene-containing polymer film, molecular reorientation and migration are strongly dependent on the polarization state of the writing beams and can be spatially modulated. Theoretical investigation by the Jones matrix method including both modulations has shown that the polarization ellipticity of ±1-order diffraction changes as a function of relief depth. Experimental results in accordance with theoretical predictions show that the polarization gratings diffract linearly and circularly polarized beams simultaneously.

We have extensively studied the electric field of the light propagating in and/or near polarization holograms by the finite-difference time-domain (FDTD) method. Polarization holograms were fabricated using photoreactive polymer liquid crystals and showed peculiar polarization conversion. This experimental observation is well-explained by the FDTD calculation. The FDTD calculation revealed the connection between the near and far field of the light transmitted through the polarization hologram.

We present the results from some experimental and theoretical studies aimed at revealing the mechanism leading to the diffraction properties of two-dimensional cross polarization gratings in photocrosslinkable polymer liquid crystals. Although the polarization gratings are overwritten at the same place, each polarization grating works independently in our material system. The above-mentioned characteristic of our cross polarization gratings originates in the grating formation mechanism in the photocrosslinkable polymer liquid crystals, in which the molecules in the solid-state polymeric materials are not reoriented during exposure and reorientation is generated during the annealing process after multiple exposure.