Birefringent Structures Research Articles

Application and validation of a viscosity approach to the existence of nanogratings in oxide glasses

Nanogratings are self-organized and sub-wavelength birefringent structures that are formed upon the action of high intensity ultrashort light pulses in the bulk of a transparent material. They have found interest in optics/photonics, microfluidics, optical data storage or sensing applications. However, the ability to successfully imprint 3-dimensional (3D) nanogratings in silicate glasses is a strong function of the glass composition. In this work, we investigate the role of glass viscosity on the ability to induce these nanogratings. We first study the nanogratings formation window in an energy-repetition rate laser parameter landscape for five common oxide glasses: SiO2 (Suprasil), GeO2, and Schott glasses AF32, Borofloat, and BK7. Secondly, and based on previous work, we define a domain of existence of the nanogratings using viscosity-based arguments. The lower limit corresponds to a temperature at which the viscosity is ∼106.6 Pa⋅s, where nanocavitation of the glass occurs, forming the nanopores that compose the nanogratings. An upper temperature limit, set for a viscosity value of ∼103.0 Pa⋅s, relates to either collapse or growth of the nanopores, resulting in the erasure of the nanopores, hence the nanogratings. The experimental results agree with the predictions made by this viscosity approach and literature data. This work opens the door to future glass viscosity engineering to maximize 3D nanogratings imprinting.

Polarization mode dispersion correction in endoscopic polarization-sensitive optical coherence tomography with incoherent polarization input states.

The incorporation of polarization sensitivity into optical coherence tomography (PS-OCT) imaging can greatly enhance utility by allowing differentiation via intrinsic contrast of many types of tissue. In fiber-based OCT systems such as those employing endoscopic imaging probes, however, polarization mode dispersion (PMD) can significantly impact the ability to obtain accurate polarization data unless valuable axial resolution is sacrificed. In this work we present a new technique for compensating for PMD in endoscopic PS-OCT with minimal impact on axial resolution and without requiring mutually coherent polarization inputs, needing only a birefringent structure with known orientation in view (such as the catheter sheath). We then demonstrate the advantages of this technique by comparing it against the current state of the art approach.

Bioactive potential of Bio‐C Pulpo is evidenced by presence of birefringent calcite and osteocalcin immunoexpression in the rat subcutaneous tissue

As the biocompatibility and bioactive potential of repair materials are desired characteristics in dentistry, the tissue response of Bio-C Pulpo, a bioceramic material launched on the marked by Angelus (Brazil), was compared with Biodentine (Septodont, France) and White MTA (WMTA; Angelus, Brazil). In 32 rats, 148 polyethylene tubes filled with Bio-C Pulpo, Biodentine or WMTA, and empty (CG, control group) were implanted into subcutaneous tissues for 7, 15, 30, and 60 days. The capsule thickness, numerical density of inflammatory cells (IC) and fibroblasts (Fb), amount of collagen, immunohistochemistry detection of interleukin-6 (IL-6) and osteocalcin (OCN), von Kossa and analysis under polarized light were performed. Data were subjected to two-way ANOVA followed by Tukey's test (p ≤ 0.05). At 7 and 15 days, the capsules around Bio-C Pulpo were thicker than in WMTA while, at 30 and 60 days, significant differences were not observed among the groups. Although at 7, 15, and 30 days, a greater number of IL-6-immunostained cells was found in Bio-C Pulpo and Biodentine than in WMTA, no significant difference was detected among the groups at 60 days. In all groups, the number of Fb and collagen content increased significantly over time. The capsules around materials exhibited von Kossa-positive and birefringent structures, and OCN-immunostained cells whereas, in the CG, these structures were not observed. Bio-C Pulpo, similarly to Biodentine and WMTA, is biocompatible, allows the connective tissue repair and presents bioactive potential in connective tissue of rats.

One-Step Synthesis of Cross-Linked Esterified Starch and Its Properties

Cross-linked esterified starch (CES) was prepared using a one-step method, where maize starch was selected as the raw material, sodium trimetaphosphate as the cross-linking agent, and acetic anhydride as the esterifying agent, respectively. A response surface experiment was systematically conducted for analyzing the correlation of the experimental variables (cross-linked temperature, pH, reaction time, sodium trimetaphosphate and acetic anhydride dosage) and properties of the product (peak and final viscosity). The Brabender viscosity, freeze-thaw stability, shearing resistance, and acid tolerance of the cross-linked acetylated dual modified starch were studied under different conditions of crosslinking degree and acetyl content. Meanwhile, the granular structure and morphology of the modified starch were analyzed. The results indicated that: after cross-linked acetylated dual modification, the starch had a distinct birefringence and granular structure, along with the creation of new carbonyl groups. The low degree of crosslinking and high acetyl contents were beneficial to the viscosity, which was significantly increased at both low and high temperatures. Moreover, the freeze-thaw stability of CES was elevated sharply after five cycles. In addition, CES displayed increased shear and acid tolerance compared to the original waxy maize, and their lowest differences between waxy maize and CES were only 0.62% and 0.59%, respectively. In summary, a novel method for starch modification was provided, and the synthesized CES was suggested to have exceptional performance for the food industry.

Numerical modeling of optical modes in topological soft matter

Vector and vortex laser beams are desired in many applications and are usually created by manipulating the laser output or by inserting optical components in the laser cavity. Distinctly, inserting liquid crystals into the laser cavity allows for extensive control over the emitted light due to their high susceptibility to external fields and birefringent nature. In this work we demonstrate diverse optical modes for lasing as enabled and stablised by topological birefringent soft matter structures using numerical modelling. We show diverse structuring of light-with different 3D intensity and polarization profiles-as realised by topological soft matter structures in radial nematic droplet, in 2D nematic cavities of different geometry and including topological defects with different charges and winding numbers, in arbitrary varying birefringence fields with topological defects and in pixelated birefringent profiles. We use custom written FDFD code to calculate emergent electromagnetic eigenmodes. Control over lasing is of a particular interest aiming towards the creation of general intensity, polarization and topologically shaped laser beams.

In vivo PS-OCT needle probe scan of human skeletal muscle.

Polarization-sensitive optical coherence tomography (PS-OCT) derived birefringence values effectively identify skeletal muscle structural disruption due to muscular dystrophy and exercise-related muscle damage in animal models in ex vivo tissue. The purpose of this investigation was to determine if a PS-OCT needle probe inserted into the leg of a human subject could accurately identify various anatomical structures with implications for use as a diagnostic tool for the determination of skeletal muscle pathology. A healthy middle-aged subject participated in this study. A custom-built PS-OCT system was interfaced with a side-viewing fiber-optic needle probe inserted into the subject's vastus lateralis muscle via a motorized stage for 3D data acquisition via rotation and stepwise pullback. The deepest recorded PS-OCT images correspond to a depth of 6 mm beneath the dermis with structural images showing uniform, striated muscle tissue. Multiple highly birefringent band-like structures with definite orientation representing connective tissue of the superficial aponeurosis appeared as the depth of the needle decreased. Superficial to these structures the dominating appearance was that of adipose tissue and low birefringent but homogeneous scattering tissue. The data indicate that a PS-OCT needle probe can be inserted into live human skeletal muscle for the identification of relevant anatomical structures that could be utilized to diagnose significant skeletal muscle pathology.

Hierarchical Modulation of Optical Anisotropy Driven by Metal Cation Polyhedra in Fluorooxoborates MII B4 O6 F2 (MII =Be, Mg, Pb, Zn, Cd).

The enhancement mechanism of birefringence is very important to modulate optical anisotropy and materials design. Herein, the different cations extending from alkaline-earth to alkaline-earth, d10 electron configuration, and 6s2 lone pair cations are highlighted to explore the influence on the birefringence. A flexible fluorooxoborate framework from AEB4 O6 F2 (AE=Ca, Sr) is adopted for UV/deep-UV birefringent structures, namely, MII B4 O6 F2 (MII =Be, Mg, Pb, Zn, Cd). The maximal enhancement on birefringence can reach 46.6 % with the cation substitution from Ca, Sr to Be, Mg (route-I), Pb (route-II), and Zn, Cd (route-III). The influence of the cation size, the stereochemically active lone pair, and the binding capability of metal cation polyhedra is investigated for the hierarchical improvement on birefringence. Significantly, the BeB4 O6 F2 structure features the shortest UV cutoff edge 146 nm among the available anhydrous beryllium borates with birefringence over 0.1 at 1064 nm, and the PbB4 O6 F2 structure has the shortest UV cutoff edge 194 nm within the reported anhydrous lead borates that hold birefringence larger than 0.1 at 1064 nm. This work sheds light on how metal cation polyhedra modulate birefringence, which suggests a credible design strategy to obtain desirable birefringent structures by cation control.

Fabrication influences on a miniaturised stokes polarimeter consisting of stacked nano-optical wire grid polarizer and retarders

The polarization properties of light can be fully controlled with nano-optical wire grid polarizers and artificial birefringent grating structures. We demonstrate an integrated polarimeter based on stacked layers of such elements. However, the optical performance of such elements is fundamentally limited and may be further altered by deviations arising from the fabrication processes. In this contribution we investigate the influences on the polarimetry performance for such a device.

PyLlama: A stable and versatile Python toolkit for the electromagnetic modelling of multilayered anisotropic media

PyLlama is a handy Python toolkit to compute the electromagnetic reflection and transmission properties of arbitrary multilayered linear media, including the case of anisotropy. Relying on a 4×4-matrix formalism, PyLlama implements not only the transfer matrix method, that is the most popular choice in existing codes, but also the scattering matrix method, which is numerically stable in all situations (e.g., thick, highly birefringent cholesteric structures at grazing incident angles). PyLlama is also designed to suit the practical needs by allowing the user to create, edit and assemble layers or multilayered domains with great ease. In this article, we present the electromagnetic theory underlying the transfer matrix and scattering matrix methods and outline the architecture and main features of PyLlama. Finally, we validate the code by comparison with available analytical solutions and demonstrate its versatility and numerical stability by modelling cholesteric media of varying complexity. A detailed documentation and tutorial are provided in a separate user manual. Applications of PyLlama range from the design of optical components to the modelling of polaritonic effects in polar crystals, to the study of structurally coloured materials in the living world. Program summaryProgram Title: PyLlama – Python Toolkit for the Electromagnetic Modelling of Multilayered Anisotropic MediaCPC Library link to program files:https://doi.org/10.17632/dzw8x5vyrv.1Developer's repository link:https://github.com/VignoliniLab/PyLlamaLicensing provisions: GPLv3Programming language: PythonSupplementary material: User guide and tutorials at https://pyllama.readthedocs.io/Nature of problem: Computation of the optical reflection and transmission coefficients of arbitrary multilayered linear media, composed of an arbitrary number of layers, possibly mixing isotropic and anisotropic, absorbing and non-absorbing materials, for linearly or circularly polarised light.Solution method: Implementation of both the transfer matrix method (faster) and the scattering matrix method (more robust) relying on a 4×4 matrix formalism.Additional comments including restrictions and unusual features: Integration of a physical model to handle cholesteric structures, blueprint for the integration of user-created custom systems, hassle-free export of spectra for non-programmers even for complex and/or custom systems. External routines include: Numpy [1], Scipy [2], as well as Sympy [3] (optional).

Orthogonal manipulations of phase and phase dispersion in realization of azimuthal angle-resolved focusings

In conventional achromatic metasurfaces configurations where the engineering paths of phase and phase dispersion are the same, limited phase dispersion control range inevitably imposes a restriction on the broadband device size, which otherwise can be arranged in a periodic manner to achieve infinite size at a single wavelength. In addition to this, the adoption of geometric-phase structures imparts the orthogonal circular polarization conversion, whereas the birefringent propagation-phase structures bring an uncertain polarization state, thus resulting in an incomplete polarization conversion. In this study, we propose an azimuthal angle-resolved beam-deflection metasurface at the same polar angle with orthogonal phase and phase dispersion control paths. Periodic expansion is implemented to achieve unlimited device size along the phase control path and the broadband light is monotonously and azimuthally deflected to the designated polar angle with the delicate design along the dispersion path. In addition, the non-crossed polarized light arising from the incomplete geometric phase control would naturally separate from the cross-polarized light when adjusting the planar geometric parameters of the birefringent metaatoms to realize dispersion control. This design scenario may find applications in phased-array detection applications where beams are azimuthally swept to search targets at one polar angle.

Single-Shot Quantitative Polarization Imaging of Complex Birefringent Structure Dynamics.

Polarization light microscopes are powerful tools for probing molecular order and orientation in birefringent materials. While a number of polarization microscopy techniques are available to access steady-state properties of birefringent samples, quantitative measurements of the molecular orientation dynamics on the millisecond time scale have remained a challenge. We propose polarized shearing interference microscopy (PSIM), a single-shot quantitative polarization imaging method, for extracting the retardance and orientation angle of the laser beam transmitting through optically anisotropic specimens with complex structures. The measurement accuracy and imaging performance of PSIM are validated by imaging a birefringent resolution target and a bovine tendon specimen. We demonstrate that PSIM can quantify the dynamics of a flowing lyotropic chromonic liquid crystal in a microfluidic channel at an imaging speed of 506 frames per second (only limited by the camera frame rate), with a field-of-view of up to 350 × 350 μm2 and a diffraction-limit spatial resolution of ~2 μm. We envision that PSIM will find a broad range of applications in quantitative material characterization under dynamical conditions.

Spatially resolved birefringence measurements with a digital micro-mirror device.

We demonstrate a novel technique to measure spatially resolved birefringence structures in an all-digital fashion with a digital micro-mirror device (DMD). The technique exploits the polarization independence of DMDs to apply holographic phase control to orthogonal polarization components and requires only a static linear polarizer as an analyzer for the resulting phase shift polarization measurements. We show the efficacy of this approach by spatially resolving complex polarization structures, including nano-structured metasurfaces, customized liquid crystal devices, as well as chiral L-Alanine and N-Acetyl-L-cystein crystals. Concentration dependent measurements of optical rotation in glucose and fructose solutions are also presented, demonstrating the technique's versatility. Unlike conventional approaches, our technique is calibration free and has no moving parts, offers high frame rates and wavelength independence, and is low cost, making it highly suitable to a range of applications, including pharmaceutical manufacturing, saccharimetry and stress imaging.

Azimuthally modulated axicon vortical beams for laser microprocessing

Non-diffracting beams have contributed greatly to recent developments in high power applications such as laser micromachining. Well known for their elongated focal region (also known as a focal line) are zeroth-order Bessel and Bessel vortical beams which allow achieving high aspect ratio modifications inside transparent materials. A superposition of several optical Bessel vortices of different topological charges allows generating high aspect ratio beams with complexly engineered transverse intensity patterns. Non-diffracting Bessel vortices commonly are created using a conical prism — an axicon. Therefore, they can be referred to as axicon beams. In this work, we have studied the formation of high power and energy axicon vortical beams both numerically and experimentally. We have inscribed sub-wavelength birefringent structures inside fused silica glass to create geometrical phase elements for the azimuthal modulation of the spatial spectra of a zeroth-order axicon (Bessel) beam which allows creating a high power superposition of several Bessel vortices. To prove the concept, we apply azimuthally modulated axicon vortical beams to create modifications inside fused silica glass samples.

Comparison of Bio-C Pulpo and MTA Repair HP with White MTA: effect on liver parameters and evaluation of biocompatibility and bioactivity in rats.

To evaluate the tissue response promoted by Bio-C Pulpo (Bio), MTA Repair HP (MTA-HP) and White MTA (WMTA) and whether these materials cause liver changes in a rat experimental model. Polyethylene tubes filled with Bio, MTA-HP and WMTA, and empty tubes (control group, CG) were implanted into the subcutaneous tissues of rats for 7, 15, 30 and 60days. Inflammatory reaction score (IRS), capsule thickness, number of inflammatory cells (IC), von Kossa reaction, interleukin-6 (IL-6) and alkaline phosphatase (ALP) immunohistochemistry reactions were performed. Combined methods, von Kossa followed by immunohistochemistry for detection of ALP, were performed. At 60days, the serum glutamic-oxaloacetic transaminase (GOT) and glutamic-pyruvic transaminase (GPT) levels were measured and liver fragments were collected for histological analysis; the data were assessed by one-way ANOVA analysis followed by Sidak's post-test. The biocompatibility and bioactivity data were subjected to the two-way ANOVA analysis followed by Tukey post hoc test, except the IRS. The IRS data were subjected to the Kruskal-Wallis ANOVA non-parametric test followed by Dunn's test (p≤.05). No significant difference was detected in serum GOT and GPT concentrations and in the number of hepatocytes among the experimental and CG samples. Although Bio-C Pulpo had the highest IC and IL-6-immunolabelled cells (p<0.0001) at all periods, no significant difference was observed in the IRS among the materials, except at 60days. In this period, the WMTA had lower IRS. All groups had a significant reduction in the capsule thickness and in the number of IC and IL-6-immunolabelled cells over time. Bio-C Pulpo, MTA-HP and WMTA specimens had greater immunoexpression of ALP than CG (p<.0001). At all periods, von Kossa-positive and birefringent structures were observed in the capsules around the materials. ALP-immunolabelled cells were also seen near von Kossa-positive structures. Bio-C Pulpo, MTA-HP and WMTA materials did not cause morphological changes in the liver and no significant alteration in the serum GOT and GPT levels. Moreover, these bioceramic materials were biocompatible and exhibited bioactive potential. However, Bio-C Pulpo induced greater inflammatory infiltrate than MTA-HP and WMTA at all periods.

Analysis and calibration of linear birefringence orientation parameters derived from Mueller matrix for multi-layered tissues

Mueller matrix polarimetry can provide abundant microstructural information of tissues. Mueller matrix polar decomposition (MMPD) is capable of extracting intrinsic polarimetric characteristics of tissue-like media, including the orientation of the linear birefringence axis. However, when measuring a multi-layered sample with linear birefringence of different orientation directions, there is a deviation between the measured and ideal values of the MMPD linear birefringence orientation parameter. Since the multi-layered anisotropic structures widely exist in biomedical samples, a modified MMPD parameter to calculate linear birefringence orientation more precisely for layered tissues is crucial. Here we propose a modified MMPD parameter to calculate linear birefringence orientation for multi-layered media. By measuring different customized phantoms and pathological tissue slices, we demonstrate that the modified parameter can show more accurately the linear birefringence orientation angle of multi-layered media. The proposed parameter can be helpful for the quantitative evaluation of not only the pathological tissue slices with fibers, but also many other material samples with layered birefringent structures.

Femtosecond laser‐induced birefringent microdomains in sodium‐borate glass for highly secure data storage

AbstractIn this paper, the inscription of polarization‐sensitive birefringent structures of two types by femtosecond laser pulses is described. Depending on the laser beam parameters, the orientation of the slow axis of birefringent structures can be either parallel or perpendicular to the polarization of the laser beam. The dependence of retardance and slow axis of birefringence on laser exposure parameters is revealed. The thermal stability of both types of structures is examined. The possibility of highly secure data storage based on the different thermal behavior of the laser‐modified region is demonstrated.

Laser Writing of Crystalline Structures in Lithium-Niobium-Germanate Glasses

It is demonstrated that spatially selective crystallization of lithium-niobium-germanate glasses with the compositions (mol.%) 25Li2O∙30Nb2O5∙45GeO2 and 30Li2O∙25Nb2O5∙45GeO2 can be formed by using a femtosecond laser beam with formation of birefringent structures containing lithium niobate. A correlation was established between the orientation of the fast axis of birefringence of crystallized tracks and the polarization plane of the laser beam.

Manifestações clínicas bucais da paracoccidioidomicose: um relato de caso

A Paracoccidioidomicose é uma doença fúngica decorrente do fungo dimórfico Paracoccidioides brasiliensis que possui predileção por lugares quentes e úmidos, por essa razão há uma grande incidência da doença no Brasil. O sítio primário da doença envolve a região pulmonar, mas com o avanço das pesquisas e estudos voltados à doença, a região da mucosa bucal vem sendo bastante afetada com o fungo. O artigo tem como objetivo demonstrar as manifestações clínicas bucais da paracoccidioidomicose em uma paciente do sexo feminino que foi diagnosticada aos 79 anos, tratada com antifúngico oral pela equipe de odontologia e encaminhada para clínica médica para tratamento da doença. A paciente apresentou lesão ulcerada de fundo moriforme com pontos hemorrágicos no rebordo alveolar direito. Foi realizada a biópsia incisional e o resultado microscópico revelou estruturas birrefringentes sugestiva de Paracoccidioidomicose. A paciente foi tratada pela equipe de odontologia da clínica odontológica da Unifenas e posteriormente encaminhada ao setor de Infectologia do Hospital Alzira Vellano, de Alfenas-MG para avaliação e tratamento dos sintomas sistêmicos. Embasado nos resultados dos exames físico, clínico e histológicos e nas características que predispõe à susceptibilidade a doença, como ser tabagista há mais de 30 anos, hipertensa e trabalhadora da zona rural, levou-se ao diagnóstico final da lesão.

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Highly sensitive near-infrared surface plasmon resonance (SPR) sensor based on birefringent six-core photonic crystal fibre

A new type of highly sensitive near-infrared birefringent six-core photonic crystal fibre sensor using surface plasmon resonance (SPR) is proposed. By using the full-vector finite element method, the impacts of the fibre parameters on the wavelength sensitivity and amplitude sensitivity are numerically studied. The numerical results indicate that, benefiting from the high birefringent multi-core fibre structure, an average sensitivity of 8083 nm/refractive index unit (RIU) within the wavelength range from 1.532 to 2.02 µm is achieved when the analyte refractive index (RI) lies in (1.372, 1.432). Moreover, the maximum amplitude sensitivity is as high as 226 RIU−1 if the analyte RI is adjusted from 1.372 to 1.382. In consideration of its excellent sensing performance, the proposed SPR multi-core PCF sensor can be applied in environmental, food safety, and (bio)chemical detection.