Birefringence Of Films Research Articles

Багатопараметрична поляризаційна джонс-матрична репрографія цифрових зображень двопроменезаломлення поліграфічних матеріалів

A model-design of the polycrystalline structure of polyethylene films is proposed. Within the framework of reprography, a method of statistical, correlation and fractal analysis of the distributions of characteristic values of graphic Jones matrix images of birefringent polyethylene films has been developed. The diagnostic efficiency of determining a set of statistical moments of the 1st - 4th orders, which characterize the distributions of characteristic values of the phase Jones matrix image of polyethylene films in the differentiation of their external mechanical and thermal deformations, has been established.

Photoinduced Anisotropy in Thin Films of Azobenzene-Containing Liquid Crystalline Supramolecular Complexes of Various Polymer Architecture.

Light patternable colorless liquid crystalline (LC) polymers are promising materials for functional photonic devices with broad applications in optical communication, diffractive optics, and displays. This work reports photoinduced optical anisotropy in thin films of azobenzene-containing (Azo) LC block copolymer supramolecular complexes, which can be decolorized after light patterning providing colorless patterned birefringent polymer films. The supramolecular complexes are prepared via intermolecular pyridine-phenol hydrogen bonding between a low-molecular-weight Azo phenol and host LC AB diblock and ABA triblock copolymers consisted of LC phenylbenzoate (PhM) blocks and poly(vinylpyridine) units. The molecular architecture of the host polymers and the morphological pattern formed by the complexes can affect orientational behavior of Azo groups under irradiation with linearly polarized light. Photoorientation of hydrogen-bonded Azo groups is accompanied by the cooperative orientation of non-photochromic PhM units, which form individual microphases and stabilize the orientation of Azo groups. This effect is specific for block copolymer complexes and it is absent for random copolymer complex, which is used as a reference sample. Optical anisotropy induced in films of the block copolymer complexes can be amplified by heating above the glass transition temperature and subsequent rinsing with diethyl ether allows colorless birefringent polymer films to be prepared.

Bioinspired transparent ultratough birefringent photonic films with engineerable interference colors derived from in-situ synthesis of CaCO3

Chameleons can rapidly modify their coloration by manipulating the arrangement of iridophores encompassing guanine crystals in their dermis, which enables incident light to undergo birefringence. Various biomaterials have been designed to mimic the arrangement of guanine crystals, yet instances of synthesizing bottom-up structures with anisotropy for optical functionality remain rare. In this study, we report a novel two-step gas diffusion method for in-situ synthesis of CaCO3 (Vaterite) within a hydrogel to fabricate a bio-photonic film displaying birefringence interference colors. This strategy enables the successful fabrication of an inorganic–organic photonic film with superior mechanical properties and flexibility, resulting in high transparency, superior toughness, and adjustable optical anisotropy. Through a combination of experiment and simulation results, we elucidated the critical role played by shape factor (distribution) and structural factor (particle size) in producing transmitted interference colors. Finally, the birefringent photonic films prepared using the dot-plate method can function as optical patterns accurately representing the “on”/“off” state within a binary system. This system offers high spatial resolution, excellent repeatability, and precise controllability of optical properties, making it applicable in fields such as information encryption and decrytion. Our study has successfully synthesized photonic material with anisotropic structure though in-situ method while elucidating the underlying mechanism governing their ability to generate transmission interference colors, thus opening up new avenues for transparent flexible polarized optics, imperceptible wearable devices, and advanced information encryption.

Modular Optical Diodes for Circular Polarization Based on Glass‐Supported Cellulose Nanocrystal/Polyethylene Glycol Composite Films

Depending on processing methods and conditions, cellulose nanocrystal (CNC) films exhibit linear birefringence or selective Bragg reflection. The latter means reflection of light with left‐handed circular polarization (LCP) due to CNC in a helicoidal microstructure of the same handedness. Herein, glass‐supported CNC/polyethylene glycol (CNC/PEG) composite films with PEG concentrations in the range of 0–30% w/w with selective Bragg reflection at wavelengths from 440 to 550 nm are prepared. A modular device comprised of a dip‐coated birefringent CNC‐glass sample sandwiched between two CNC/PEG‐glass samples shows different responses to light with LCP and to light with right‐handed circular polarization (RCP). The device suppresses selective Bragg reflection from the rear (front) CNC/PEG sample for incident light with LCP (RCP), even when the birefringent film does not meet the condition for a halfwave plate. This behavior resembles the performance of optical diodes for circular polarization. Polarization properties of composite films and optical diodes in terms of degree of polarization and ellipticity are discussed within the Stokes–Mueller formalism. Electromagnetic simulations of Mueller matrices reveal the equivalence of modular and in‐tandem film approaches of optical diodes.

Investigating the Trade‐off between Optical and Mechanical Properties during Constrained Sintering of Mesomorphic Ceramic Films

AbstractRobust, transparent, and birefringent inorganic films are demanded for polarization control of high‐power lasers. While single crystals or films obtained via glancing angle deposition exhibit desirable optical properties and laser damage resistance, these methods are limited by cost and scalability. Mesomorphic ceramics as inorganic solids with liquid crystalline superstructure offer appealing transparency and birefringence but lack mechanical robustness due to their high porosity. Here, the effect of sintering on optical and mechanical properties of mesomorphic ceramics is evaluated. Films prepared by blade coating are sintered under varying conditions. Constrained sintering accomplished crystallite growth, densification, and morphological changes including necking as well as cracking while preserving the crystallographic orientation. The extent of sintering as a function of thermal treatment is quantified by morphology, surface area loss, and crystallite growth. Moreover, activation energies for surface diffusion and grain growth are estimated by surface area analysis and X‐ray diffraction peak narrowing, respectively. After sintering, birefringence decreases while Young's modulus and hardness improve as the film densifies. Upon partial sintering, mesomorphic ceramics retain transparency, high birefringence, and enhanced modulus. Laser‐induced damage threshold is measured as well. The reported results represent an important step toward the assembly and sintering of robust waveplates with high laser damage resistance.

Transparent Multicolor Electrochromic Displays with Ingenious Hues Adjustment by Integrating Cholesteric Liquid Crystal with Viologen Gel

AbstractThe colorization of electrochromic displays (ECDs) has become an intriguing hotspot with fast‐growing demands for the development of displays. Reported colorful inorganic ECDs incorporating optical nanocavity or metal‐dielectric stacks sacrifice transparency and have intrinsic structural color, thus confining plenty of applications as transparent displays. Additionally, most transparent ECDs adopt plane alignments of EC materials that can only show one or several kinds of colors under electrical stimuli. Herein, vertically stacked viologen‐based ECDs integrating cholesteric liquid crystal (CLC) are proposed. By applying voltage, rotation, and changing chiral dopants’ concentration, the combined ECDs show enlarged color palette and multi‐mode color modulation. Moreover, red, blue, and green viologen gels are also synthesized by producing dioctyl‐, diethyl‐, and diphenyl‐substituted dipyridyl, which exhibit outstanding performance in terms of high optical variation, fast response speed, long cyclability, etc. Furthermore, the palette area of the CLC layers is dramatically expanded about 5 times more than reported by introducing a birefringent film. The vertically stacked ECDs integrate merits of both CLCs (high color purity and rich hues) and viologens (large variation and low voltage response), which will likely encourage attempts at three‐dimensional colorful EC displays and broaden its applications.

High sensitivity ethanol vapor sensor based on a nematic liquid crystal film embedded optical fiber Sagnac interferometer

Interferometric optical fiber sensors have become the preferred choice for ethanol vapor detection because of their high sensitivity and figure of merit. However, the response time of interferometric fiber optic ethanol vapor sensors is very long. To address this issue, we experimentally investigated an ethanol vapor sensor based on a nematic liquid crystal (NLC) film embedded optical fiber Sagnac interferometer. The high birefringent NLC film, which worked as the sensing media of ethanol vapor for its absorption of ethanol vapor, was penetrated into the Sagnac ring to generate the spectral interference. The results showed that the measurement sensitivity of ethanol gas concentration reached 2.22 pm ppm−1. The detection range was about 1210 ppm–10 000 ppm. Most importantly, the response time of the proposed sensor is only 15 s. The designed sensor, which showed the advantages of fast response, high sensitivity, and stability, could be a competitive candidate for ethanol vapor sensing.

Zero–Zero Birefringence Cellulose Acetate-Based Optical Films by Benzoylation

Zero–zero birefringence film is one of the key components in optical displays, and its design and preparation remain a challenge nowadays. Here, we report the synthesis of benzoylated cellulose acetate (BCA), the preparation of BCA films by solution casting, and the birefringent properties of unstretched and stretched BCA films. It is found that zero–zero birefringence films can be fabricated using both unstretched and stretched BCA films. As the degree of substitution of benzoyl (DSBz) increases, the out-of-plane birefringence (Δnth) gradually decreases and changes from positive to negative. Particularly, for DSBz = 0.511, both the in-plane birefringence (Δnin) and out-of-plane birefringence (Δnth) of stretched BCA films are close to zero. The orientations of the acetyl and benzoyl groups under stretching are measured to interpret the underlying compensation mechanisms. Finally, we show that the wavelength dispersion of BCA films with DSBz = 0.511 varies significantly with the increase in draw ratio, and formulize the normalized birefringence with the relative orientation degree of the benzoyl and acetyl groups. Our results suggest that the birefringence and wavelength dispersion of cellulose acetate-based optical films can be well regulated by a combination of chemical modification and stretching, and have potential significance to the industrial production of zero–zero birefringence films.

Thermally stable birefringent films from a liquid crystalline polymer having side groups containing N-benzylideneaniline

Polymethacrylate liquid crystalline polymer having side groups containing N-benzylideneaniline moiety was synthesized, and its photoinduced reorientation behavior was investigated using linearly polarized UV light. Films of these polymer exhibited axis-selective trans-cis-trans photoreorientation of the side groups upon irradiation. Annealing the film in the liquid crystalline temperature range of the polymer after irradiation greatly amplified their otherwise minimal photo-induced optical anisotropy. Due to the extended mesogenic structure of the side groups, the polymer showed significant thermal stability and a high degree of optical anisotropy after annealing.

Shear-Coated Linear Birefringent and Chiral Cellulose Nanocrystal Films Prepared from Non-Sonicated Suspensions with Different Storage Time.

Nanocelluloses are very attractive materials for creating structured films with unique optical properties using different preparation techniques. Evaporation-induced self-assembly of cellulose nanocrystals (CNC) aqueous suspensions produces iridescent films with selective circular Bragg reflection. Blade coating of sonicated CNC suspensions leads to birefringent CNC films. In this work, fabrication of both birefringent and chiral films from non-sonicated CNC suspensions using a shear-coating method is studied. Polarization optical microscopy and steady-state viscosity profiles show that non-sonicated CNC suspensions (concentration of 6.5 wt%) evolve with storage time from a gel-like shear-thinning fluid to a mixture of isotropic and chiral nematic liquid crystalline phases. Shear-coated films prepared from non-sonicated fresh CNC suspensions are birefringent, whereas films prepared from suspensions stored several weeks show reflection of left-handed polarized light. Quantification of linear and circular birefringence as well circular dichroism in the films is achieved by using a Mueller matrix formalism.

Azobenzene-containing liquid crystalline block copolymer supramolecular complexes as a platform for photopatternable colorless materials

Using liquid crystalline triblock copolymer complexes with hydrogen-bonded azobenzene moieties, photopatterned colorless birefringent films were prepared by irradiation with linearly polarized light and subsequent extracting azobenzene moieties.

Gas Sensing Through Mixed Polarization in Birefringent Porous Silicon Thin Film

We interrogate a sensor based on a highly birefringent film, irradiated by an incident beam whose polarization is oriented 45° with respect to the normal film axes. The reflected spectrum is shown to display exceptional features and resolve some outstanding issues in interferometric sensing. By means of optical signal processing based on Fourier analysis, three different periodicity patterns can be elucidated when sensing a single event, improving the sensing process in several ways: It allows sensing at several sensitivity scales, and it clears out the problems of phase and direction ambiguities. A novel effect is observed in which the phase displacement of different patterns move in opposite directions as sensing takes place. We present a theoretical analysis of the process, as well as experimental measurements with different ethanol concentrations.

Highly chromatic retardation via multi-twist liquid crystal films

Here we study birefringent films with highly customizable chromatic retardation spectra, using multi-twist liquid crystal (LC) films. These are made of two or more layers of chiral nematic LC polymer network materials, also known as reactive mesogens, which form a monolithic thin-film wherein the in-plane orientation of subsequent layers is automatically determined by the single alignment layer on the substrate. The multiple layer thicknesses and twists present many degrees of freedom to tailor the retardation. While prior work examined achromatic spectra, here we show how to use Mueller matrix analysis to create highly chromatic spectra. We experimentally demonstrate both a uniformly aligned retarder as a green/magenta color filter and a “hot” polarization grating (PG) that diffracts infrared while passing visible light. The three-twist color filter shows a contrast ratio in transmittance between polarizers as high as 10:1 between the half- and zero-wave retardation bands. The “hot” PG shows an average first-order efficiency of about 90% for 1000–2700 nm and an average zero-order efficiency of about 90% for 500–900 nm. The principles here can be extended to nearly any chromatic retardation spectra, including high/low/bandpass, and to nearly any LC orientation pattern, in general known as geometric-phase holograms.

Linear Birefringent Films of Cellulose Nanocrystals Produced by Dip-Coating.

Transparent films of cellulose nanocrystals (CNC) are prepared by dip-coating on glass substrates from aqueous suspensions of hydrolyzed filter paper. Dragging forces acting during films’ deposition promote a preferential alignment of the rod-shaped CNC. Films that are 2.8 and 6.0 µm in thickness show retardance effects, as evidenced by placing them between a linearly polarized light source and a linear polarizer sheet in the extinction configuration. Transmission Mueller matrix spectroscopic ellipsometry measurements at normal incidence as a function of sample rotation were used to characterize polarization properties. A differential decomposition of the Mueller matrix reveals linear birefringence as the unique polarization parameter. These results show a promising way for obtaining CNC birefringent films by a simple and controllable method.

Polarization-sensitive beam steering from quantum emitters coupled with birefringent metamaterials.

One-dimensional metal/dielectric subwavelength periodic patterns have dielectric or metallic material dispersions depending on the polarization of incident light. This feature enables the development of artificial, ultrathin, birefringent films. In this study, we report polarization-sensitive beam steering from quantum emitters coupled with one-dimensional metal/dielectric metamaterial films. Electromagnetic simulations show that an Al/ITO metamaterial film functioning as a quarter-wave plate leads to vertically directed radiation for one polarization and a saddle-shaped, diverging radiation pattern for the orthogonal polarization. The strategy studied herein is extended to achieve polarized, vertically directed emission from organic light-emitting diodes. A tailored Al/ITO metamaterial mirror yields an approximately 30-fold improvement in polarization ratio, in conjunction with polarization-dependent Purcell factor enhancement.

New fabrication approach to develop a high birefringence photo-crosslinked film based on a sulfur-containing liquid crystalline molecule with large temperature dependence of birefringence

ABSTRACTWe present a new fabrication approach to achieve a high birefringence film by means of photopolymerization based on an alkylthio-containing rod-like liquid crystalline molecule exhibiting large temperature dependence of birefringence. We designed a new reactive mesogen having alkylthio linkages (BPM–S). It was found that BPM–S had a larger increment of birefringence with decreasing temperature, relative to commercially available alkoxy analog LC242. This result could be thought to be due to enhanced intermolecular attractive interaction for an alkylthio mesogen implied by the proximity of laterally neighboring molecules and cybotactic nematic tendency based on wide-angle X-ray measurement. The uniaxially-aligned photo-polymerized film for BPM–S showed higher birefringence than that for LC 242.

Optical coating on a corrugated surface to align the polarization of an unpolarized wave without loss

A multilayer comprising birefringent thin films is devised to present to function as a polarization beam splitter and waveplate simultaneously. By arranging such a multilayer on a right triangle-shaped corrugated surface, a polarizer is realized to align the randomly oscillating electric field of an unpolarized wave into a linear polarized wave without loss.

Optical manipulation and defect creation in a liquid crystal on a photoresponsive surface.

Light-induced modulations of the refractive index and pattern formation are desirable to generate complex photonic structures via exposure to light. Here we show that local modulations of the effective refractive index and reconfigurable defects can be locally induced in a hybridized thin birefringent film of a nematic liquid crystal (LC) on a photoresponsive (generating photoinduced electric fields) iron doped lithium niobate surface via exposure to a focused laser beam. Samples were studied with a tailored imaging approach, which provided the ability to investigate these optically excited, field-induced responses on a microscopic level. Upon exposure with a focused laser beam, the fluent LC was expanded on the substrate's surface and localized field-induced defects were optically created. Both umbilic (central) and line defects were observed. The formation of field-induced umbilic defects was modeled in numerical simulations. In addition, line defects were experimentally studied. It was seen that line defects interconnected the centers of two central defects (field-induced defects, which were present at the upper and lower surfaces of the LC layer). In addition, line disclinations separating reverse tilt domains (caused by the inhomogeneous distribution of the photogenerated fields) were seen. These line disclinations were pinned to the central defects. By exposure with two adjacent focused laser beams two umbilic defects were created side by side and interconnected with a line defect (the line defects pinned to each umbilic defect were joined in a single defect line). An alternative technique is presented to field-induce promising photonic motives (microlenses, resonators, line defects) in a liquid crystalline, hybridized birefringent film on a microscopic scale by using a low-power laser (opposed to the high power necessary to induce optical Kerr responses in a neat LC).

Zero birefringence films of pullulan ester derivatives

High-performance films with almost zero-birefringence and zero-wavelength dispersion were succeeded to prepare from pullulan esters derivatives (PLEs) without any additives. Optical transmittance analysis, birefringence measurement of PLE cast film and hot stretched films, and infrared dichroism analysis were conducted to characterize optical properties of PLE films comparing with cellulose triacetate which is commercially used as low-birefringence in optical devices. The aims of this study, characterization of optical properties of pullulan esters, can develop a deep understanding of the fundamental knowing and applicability of polysaccharides. Accordingly, authors believe this paper will open the gate for researches in the application of polysaccharides.

Thermostable birefringent copolyimide films based on azobenzene-containing pyrimidine diamines

This work shows the key role played by the chemical structure of polyimides in the thermal stability of birefringence.