Birefringence Properties Research Articles

Thermal, Mechanical, and Optical Properties of Maleimide Copolymers Containing Twisted N‐Phenyl Substituents in the Side Chain

AbstractUV absorption spectroscopic measurements and DFT calculations revealed that N‐(alkyl‐substituted phenyl)maleimides with substituents at the ortho position favored a twisted N‐phenyl conformation, due to the steric hindrance between the maleimide ring and the substituted N‐phenyl moiety. High‐molecular‐weight copolymers were synthesized by radical copolymerization of the N‐(alkyl‐substituted phenyl)maleimides with n‐butyl vinyl ether and n‐butyl acrylate. The thermal properties of the copolymers were determined by thermogravimetric analysis and differential scanning calorimetry. The mechanical tensile tests under temperature control revealed the mechanical features of the copolymers depending on their repeating structure and composition. The significant temperature dependence of the modulus and strain of the copolymers was also clarified. Then, the transparency, refractive indices, and birefringence properties of the copolymer films were evaluated. It was confirmed that the maleimide copolymers had negative orientational birefringence with small absolute values and positive photoelastic birefringence. The effect of the conformational structure of the N‐phenyl groups on the thermal, mechanical, and optical properties of the copolymers was discussed.

Input polarization-independent polarization-sensitive optical coherence tomography using a depolarizer.

Polarization-sensitive optical coherence tomography is gaining attention because of its ability to diagnose certain pathological conditions at an early stage. The majority of polarization-sensitive optical coherence tomography systems require a polarization controller and a polarizer to obtain the optimal polarization state of the light at the sample. Such systems are prone to misalignment since any movement of the optical fiber normally coupled to the light source will change the polarization state of the incident beam. We propose and demonstrate an input polarization-independent polarization-sensitive optical coherence tomography system using a depolarizer that works for any input polarization state of the light source. The change in the optical power at the sample for arbitrary input polarized light for the standard polarization-sensitive optical coherence tomography system was found to be approximately 84% compared to 9% for our proposed method. The developed system was used to measure the retardance and optical axis orientation of a quarter-wave plate and the obtained values matched closely to the expectation. To further demonstrate the capability of measuring the birefringent properties of biological samples, we also imaged the nail bed. We believe that the proposed system is a robust polarization-sensitive optical coherence tomography system and that it will improve the diagnostic capabilities in clinical settings.

Design and analysis of dispersion-compensating chalcogenide photonic crystal fiber with high birefringence

The photonic crystal fiber (PCF) with a bunch of air holes enclosing the silica core field has momentous and compelling attributes when compared with the ordinary single-mode fibers. In this work, both the birefringence and dispersion properties of a polarization-maintaining chalcogenide (ChG) photonic crystal fiber are numerically investigated by means of the finite element method. Through simulation, it is found that the birefringence of the proposed $${\mathrm{G}\mathrm{e}}_{11.5}{\mathrm{A}\mathrm{s}}_{24}{\mathrm{S}\mathrm{e}}_{64.5}$$ PCF can reach as high as $$0.03$$ when compared with the conventional fiber that has merely $$5\times {10}^{-4}$$ for wavelengths in the 2–10 $$\upmu \mathrm{m}$$ range. The PCF is designed with zero-dispersion wavelengths for x- and y-polarized modes in the 2–10 $$\upmu \mathrm{m}$$ range. It is also observed that over the entire MIR wavelength range, the GVD remains positive and has a maximum value of 30,000 ps2/nm-km. Hence, the proposed $${\mathrm{G}\mathrm{e}}_{11.5}{\mathrm{A}\mathrm{s}}_{24}{\mathrm{S}\mathrm{e}}_{64.5}$$ PCF plays the dual role of acting as a very good polarization-maintaining fiber due to its very high birefringence and an excellent dispersion-compensating fiber due to its large positive GVD. This $${\mathrm{G}\mathrm{e}}_{11.5}{\mathrm{A}\mathrm{s}}_{24}{\mathrm{S}\mathrm{e}}_{64.5}$$ PCF serves as a very good candidate for ultra-broadband high bit-rate transmission. Supercontinuum generation is another important application of PCF. Supercontinuum generation is a generation of coherent and broadband light. SC generation in PCFs has several applications in optical coherence tomography (OCT), optical frequency metrology (OFM), pulse compression, and design of ultrafast femtosecond laser pulses.

Thermotropic cholesteric liquid crystals. Thermo-morphologic, optical refracting and birefringent properties: Direct and reverse phase transitions

Abstract Temperature dependences of the average refractive index 〈n〉, refractive indices of the ordinary ray no and the extraordinary ray ne, and the birefringence Δn have been investigated in two cholesteric liquid crystals. Investigations have been carried out for the heating – cooling reversible cycle. Thermal hysteresis for the ne = ne(T), no = no(T) and ∣Δn ∣ = ∣ Δn ∣ (T) and also shift of the reverse isotropic liquid state – cholesteric mesophase phase transition to lower temperatures have been found. Comparative estimations of temperature changes of the 〈n〉, no, ne and ∣Δn∣ with the thermo-morphologic properties of the heterophase regions of the direct cholesteric mesophase – isotropic liquid state and reverse isotropic liquid state – cholesteric mesophase phase transitions have been carried out. Results of investigations exhibit connection of temperature behavior of the optical properties and the thermo-morphologic peculiarities of the heterophase regions, and indicate that phase transition between cholesteric mesophase and isotropic liquid state is the first order.

Single-photon-level narrowband memory in a hollow-core photonic bandgap fiber

An experimental platform operating at the level of individual quanta and providing strong light-matter coupling is a key requirement for quantum information processing. In our work, we show that hollow-core photonic bandgap fibers filled with laser-cooled atoms might serve as such a platform, despite their typical complicated birefringence properties. To this end, we present a detailed theoretical and experimental study to identify a fiber with suitable properties to achieve operation at the single-photon level. In the fiber, we demonstrate the storage and on-demand retrieval as well as the creation of stationary light pulses, based on electromagnetically induced transparency, for weak coherent light pulses down to the single-photon level with an unconditional noise floor of 0.017(4) photons per pulse. These results clearly demonstrate the prospects of such a fiber-based platform for applications in quantum information networks.

The effect of temperature and pressure on polycaprolactone morphology

The morphology and melting behavior of poly(ε-caprolactone) (PCL) processed at varying pressure-temperature-time conditions (2000–20,000 lbf, 22–70 °C, and 5–15 min) were studied using polarized light microscopy (PLM), differential scanning calorimetry (DSC), and X-Ray diffraction (XRD). Samples processed well below the melting region at 22 °C displayed minimal to no birefringent properties, with broadened crystalline XRD scattering patterns, indicative of plastic crystal mesophase morphology. Plastic crystal quantity was shown to gradually increase from 16% to 30% with processing pressure increasing from 2000 lbf to 20,000 lbf. The mechanism of this formation is thought to be the result of crystal disorganization upon plastic deformation, related to the low-energy barrier slip-planes in the crystalline structure. With sufficient chain mobility achieved at higher processing temperatures (50 °C and 60 °C), samples displayed broad birefringent strokes under PLM and were characterized by XRD scattering patterns of broad anisotropic arcs around the equator of the 2D azimuthal pattern, which are indicative of condis crystal mesophase orientation. As opposed to plastic crystal, the condis crystal quantities showed no correlation with increased pressure, ranging between 28% and 40% as processing pressure increased. The additional chain mobility at these temperatures is thought to enable the mesophase to orient radially (normal to the direction of the external load), allowing the transition from plastic crystal to condis crystal. Thus, this paper reports the formation of four distinct morphologies upon processing PCL namely; crystalline, condis crystal mesophase, plastic crystal mesophase, and amorphous.

Birefringence and photoluminescence properties of diphenylacetylene-based liquid crystal dimers

We herein report phase transitions, mesomorphism, birefringence behavior and photoluminescence properties of symmetric liquid crystal (LC) dimers based on diphenylacetylene or tolane.

Facile synthesis of cesium trithiocyanurate with high ionic conductivity and large birefringence properties

A new trithiocyanurate with enhanced proton conductivity and large birefringence has been synthesized by a facile aqueous solution method.

A liquid-crystal-based immunosensor for the detection of cardiac troponin I.

Cardiac troponin I (cTnI) is one of the most sensitive and specific markers of myocardial cell injury, which can detect even minor myocardial damages. It is recognized as the main biochemical marker of the rapid diagnosis of acute myocardial infarction (AMI) and acute coronary syndrome (ACS). In this study, a label-free biosensor that utilizes the birefringence property of a nematic liquid crystal (LC) for the detection of cTnI is demonstrated. A chemically sensitive film with specific molecular recognition ability was decorated on the surface of a substrate, and the LC molecules were arranged in a vertically oriented order under the influence of the sensitive film, and a dark background signal was obtained using a polarizing optical microscope. When the antigen-antibody specifically binds to form a stronger acting force, the orientation of the LC molecules changes, resulting in a bright optical appearance. This LC-based immunosensor not only has the advantages of a facile structure, low cost and excellent specificity but also high sensitivity (a low detection limit of 1 pg ml-1), and has a promising future in biomedical related fields.

Polarimeter for measuring the properties of birefringent media in reflective mode.

This work presents a description of a polarimetric system for measuring the properties of birefringent media. In our reflection system the applied Stokes polarimeter acts both as a generator of the light's selected polarization states as well as a light analyzer leaving the examined medium. The method is based on six intensity distribution measurements realized in six different configurations of polarizers/analyzers: four linear and two circular ones. Thus, we have achieved parallel polariscope for linear polarizers and the crossed polariscope for circular polarizers. Such a setup can be easily applied for linearly birefringent media properties measurements including dichroic ones. This measurement setup and the measurement method were successfully tested in a homogeneous medium and a medium with variable phase difference.

Effective structural chirality of beetle cuticle determined from transmission Mueller matrices using the Tellegen constitutive relations

Several beetle species in the Scarabaeoidea superfamily reflect left-handed polarized light due to a circular Bragg structure in their cuticle. The right-handed polarized light is transmitted. The objective here is to evaluate cuticle chiral properties in an effective medium approach using transmission Mueller matrices assuming the cuticle to be a bianisotropic continuum. Both differential decomposition and nonlinear regression were used in the spectral range of 500–1690 nm. The former method provides the sample cumulated birefringence and dichroic optical properties and is model-free but requires a homogeneous sample. The materials chirality is deduced from the circular birefringence and circular dichroic spectra obtained. The regression method requires dispersion models for the optical functions but can also be used in more complex structures including multilayered and graded media. It delivers the material properties in terms of model functions of materials’ permittivity and chirality. The two methods show excellent agreement for the complex-valued chirality spectrum of the cuticle.

Cellulose-Based Microparticles for Magnetically Controlled Optical Modulation and Sensing.

Responsive materials with birefringent optical properties have been exploited for the manipulation of light in several modern electronic devices. While electrical fields are often utilized to achieve optical modulation, magnetic stimuli may offer an enticing complementary approach for controlling and manipulating light remotely. Here, the synthesis and characterization of magnetically responsive birefringent microparticles with unusual magneto-optical properties are reported. These functional microparticles are prepared via a microfluidic emulsification process, in which water-based droplets are generated in a flow-focusing device and stretched into anisotropic shapes before conversion into particles via photopolymerization. Birefringence properties are achieved by aligning cellulose nanocrystals within the microparticles during droplet stretching, whereas magnetic responsiveness results from the addition of superparamagnetic nanoparticles to the initial droplet template. When suspended in a fluid, the microparticles can be controllably manipulated via an external magnetic field to result in unique magneto-optical coupling effects. Using a remotely actuated magnetic field coupled to a polarized optical microscope, these microparticles can be employed to convert magnetic into optical signals or to estimate the viscosity of the suspending fluid through magnetically driven microrheology.

Active compensation of extrinsic polarization errors using adaptive optics.

We present a scheme for active compensation of complex extrinsic polarization perturbations introduced into an optical system. Imaging polarimeter is used to measure the polarization state across a beam profile and a liquid crystal spatial light modulator controls the polarization of the input beam. A sequence of measurements permits determination of the birefringence properties of a perturbing specimen. The necessary correction is calculated and fed back to the polarization modulator to compensate for the polarization perturbation. The system capabilities are demonstrated on a range of birefringent specimens.

Photo-active chitosan-based hybrid films

Biodegradable films for food packaging have received increasing attention from the industry in recent years. Due to its extraordinary properties, chitosan has demonstrated to be an exceptional candidate for that kind of applications. In this study, chitosan-based films modified with an azopolymer and silver nanoparticles were prepared by solvent-casting. The quality and homogeneity of the samples was satisfactory and films with thicknesses of the order of 25 µm and of various sizes, with diameters ranging from 5 to 15 cm, were obtained. The developed hybrid films were characterized by several experimental techniques including: atomic force microscopy, attenuated total reflectance-Fourier transformed infrared spectroscopy, thermogravimetric analysis, ultraviolet–visible spectroscopy and water contact angle measurements. In addition, the mechanical properties of the samples were investigated. Specifically, the tensile strength and the elastic modulus were enhanced in the films modified with azopolymer and silver nanoparticles. Moreover, the developed films showed reversible induced birefringence properties, indicating that they could be used for optical storage applications.

Polarization properties of nematic liquid crystal cell with tapered optical fiber

Abstract In the paper, an extended analysis of the polarization properties of a liquid crystal cell with a biconically tapered single-mode telecommunication optical fiber was presented. These properties are a result of a sample geometry and used LC materials. They were analyzed by using two theoretical models based on the matrix decomposition methods, i.e., polar and singular-value one. By measuring Mueller matrices, information about losses, depolarization, dichroism and birefringence was obtained. In the experiment two types of tested samples filled with well-known 6CHBT and E7 liquid crystals were prepared and all optical parameters were shown as the voltage dependence. The tested samples have dichroic properties and for both models calculated PDL is similar and it increases from 2.6 to 6.6 dB for E7 and from 0.4 to 2.7 dB for 6CHBT with voltage changes within the range of 40 – 190 V. Optical losses simultaneously decrease from 30 dB to 27 dB and from 36 dB to 28 dB, respectively. The birefringence properties cannot be directly comparable due to differences between both applied models but voltage fluctuations of these parameters are not significant. These results confirm expected dichroic properties of designed device and complete knowledge about its working principles. Moreover, presented analysis validates usefulness of the singular-value decomposition model applied to dichroic optical fiber elements.

Optical Polarimetric Detection for Dental Hard Tissue Diseases Characterization.

Dental enamel constitutes the outer layer of a crown of teeth and grows nearly parallel. This unique nanostructure makes enamel possess birefringence properties. Currently, there is still no appropriate clinical solution to examine dental hard tissue diseases. Therefore, we developed an optical polarization imaging system for diagnosing dental calculus, caries, and cracked tooth syndrome. By obtaining Stokes signals reflected from samples, Mueller images were constructed and analyzed using Lu-Chipman decomposition. The results showed that diattenuation and linear retardance images can distinguish abnormal tissues. Our result also aligns with previous studies assessed by other methods. Polarimetric imaging is promising for real-time diagnosing.

Controlling spatial hole burning in lasers using anisotropic laser mirrors

The concept of the twisted-mode laser operation, which suppresses spatial hole burning and produces single-mode operation in a standing-wave resonator, is revisited for the case of optically anisotropic laser mirrors presenting arbitrary birefringent and dichroic properties. Our analysis clarifies the relationship between the mirrors’ optical properties and the proximity of the polarization states of the counterpropagating waves, which determines the contrast of the standing-wave pattern inside the resonator. The intensity of the principal mode and the population of the upper laser level as a function of the pumping rate are then determined analytically, which enables estimates of the slope efficiency and threshold of multimode emission for a given contrast value of the standing wave. The inversion density is found to reach an upper bound as a function of the pumping rate for every value of the contrast except unity. The design rules for anisotropic mirrors to produce single-frequency operation are provided that are less strict than those to achieve pure twisted-mode operation.

Investigation of Stress Field and Fracture Development During Shale Maturation Using Analog Rock Systems

The emergence of hydrocarbons within shale as a major recoverable resource has sparked interest in fluid transport through these tight mudstones. Recent studies suggest the importance to recovery of microfracture networks that connect localized zones with large organic content to the inorganic matrix. This paper presents a joint modeling and experimental study to examine the onset, formation, and evolution of microfracture networks as shale matures. Both the stress field and fractures are simulated and imaged. A novel laboratory-scale, phase-field fracture propagation model was developed to characterize the material failure mechanisms that play a significant role during the shale maturation process. The numerical model developed consists of coupled solid deformation, pore pressure, and fracture propagation mechanisms. Benchmark tests were conducted to validate model accuracy. Laboratory-grade gelatins with varying Young’s modulus were used as scaled-rock analogs in a two-dimensional Hele-Shaw cell apparatus. Yeast within the gelatin generates gas in a fashion analogous to hydrocarbon formation as shale matures. These setups allow study and visualization of host rock elastic-brittle fracture and fracture network propagation mechanisms. The experimental setup was fitted to utilize photoelasticity principles coupled with birefringence properties of gelatin to explore visually the stress field of the gelatin as the fracture network developed. Stress optics image analysis and linear elastic fracture mechanics (LEFM) principles for crack propagation were used to monitor fracture growth for each gelatin type. Observed and simulated responses suggest gas diffusion within and deformation of the gelatin matrix as predominant mechanisms for energy dissipation depending on gelatin strength. LEFM, an experimental estimation of principal stress development with fracture growth, at different stages was determined for each gelatin rheology. The interplay of gas diffusion and material deformation determines the resulting frequency and pattern of fractures. Results correlate with Young’s modulus. Experimental and computed stress fields reveal that fractures resulting from internal gas generation are similar to, but not identical to, type 1 opening mode.

Sensing of cocaine using polarized optical microscopy by exploiting the conformational changes of an aptamer at the water/liquid crystal interface.

Liquid crystals (LCs) have the ability to transduce and amplify a molecular stimulus into optical signals due to their elastic and birefringence properties. An aptamer-based LC sensor for cocaine is described here. 3-Morpholinopropanesulfonic acid with amphipathic structure was used to establish recognition sites at a water/LC interface for the detection of cocaine. The cocaine-binding aptamer is formed at the interface. The conformation of the aptamer undergoes a change on binding cocaine, and this triggers the LCs anchoring transition from homeotropic to planar. Binding can also be detected by polarized optical microscopy. The fluorescence spectroscopy and circular dichroism results are used to prove that the conformation of aptamer changed from a hairpin structure to a special three-way junction structure on binding of cocaine at the interface. The assay works in the 1nM to 10μM cocaine concentration range and is specific. Graphical abstract Schematic representation of aptamer-based liquid crystal (LC) biosensor for the detection of cocaine. In this interface biosensing system, after the aptamer binding with cocaine, the conformation of aptamer at the aqueous/LC interface was changed from a hairpin structure to a special three-way junction structure. This triggered the Liquid crystals (LCs) anchoring transition from homeotropic to planar and the sign-on optical signal could be obtained by polarizing optical microscope (POM) in real-time.

Tunable birefringence in silica mediated magnetic fluid

The present study reports magnetic and optical properties of silica mediated lauric acid stabilized magnetic fluids. The tunable birefringence (Δn) and other properties are investigated as a function of (i) concentrations of silica suspension, and (ii) saturation magnetization (MS) 0.5099 kA m−1 (FN30) and 1.2855 kA m−1 (F30) of magnetite magnetic fluid (MF). The study reveals that Δn suppresses on addition of silica in FN30, whereas enhances (up to critical concentrations of silica) in F30. The magnetic field induced chain observed in the FN30 based fluids are long, thick and scattered, while short, thin and dense chains emerges in F30 based fluid. The magnetic field induced assembly and the magnetic parameters correlates with the results of Δn. The particle size analysis indicates increment of particle size on addition of silica nanoparticles. The thermogravimetry analysis confirms the direct interaction of silica nanoparticles and the lauric acid coated magnetite particles. This is the first report of direct interaction of silica—magnetite magnetic fluids, and its subsequent effect on tunable birefringence and other properties.