Birefringence Response Research Articles

Designing Polar Covalent Hybrid Cadmium‐Based Chalcohalides Ultraviolet Nonlinear Optical Crystal with Strong Optical Anisotropy via Double‐Site Dual FBUs Tailoring

AbstractThe pressing demand for both established and innovative technologies to expand laser wavelengths has rendered high‐performance nonlinear optical (NLO) crystals with large optical anisotropy indispensable. Here, centrosymmetric [SHC(NH2)2]2CdBr4 (1) and pseudo‐2D layered [SC(NH2)2]2CdBr2 (2), as well as pseudo‐3D noncentrosymmetric [SC(NH2)2]2CdCl2 (3) are successfully synthesized through the introduction of π‐conjugated SC(NH2)2 groups. Compared to ionic compound 1 containing full‐halogen coordination tetrahedra, covalent compounds 2 and 3 featuring novel polar [SC(NH2)2]2CdX2 (X = Br, Cl) tetrahedral units demonstrate enhanced bandgaps (>4 eV) and birefringences (>0.3@546 nm) due to the unique coordination environment. Remarkably, 3 exhibits a strong second‐harmonic generation (SHG) response (2.1 × KH2PO4(KDP)), high laser‐induced damage thresholds (30 × AgGaS2(AGS), and excellent water stability. The birefringence of 3 is the largest among the hybrid halides NLO crystals containing d10 metal cations. Detailed theoretical calculations confirm that such a modified double‐site dual functional building units (FBUs) substitution is an effective strategy for designing superior optical materials with large birefringence and strong SHG response, paving the way for the development of high‐performance devices in related fields.

Simultaneous measurement of liquid refractive index and temperature based on the birefringence response of a water-filled D-shaped photonic crystal fiber

In this paper, a water-filled D-shaped photonic crystal fiber (WFDSPCF) sensor based on the birefringence response for simultaneously measuring the liquid refractive index (LRI) and liquid temperature (LT) is proposed. We undertake theoretical and simulation calculations, and the results show that the proposed WFDSPCF can achieve ultrahigh LRI and LT sensitivities when operating around the group birefringence turning point. By optimizing the structural parameters, the proposed WFDSPCF sensor can achieve LRI and LT sensitivities of -25642.86 nm/RIU and 12.8 nm/°C, respectively. In addition, in order to eliminate the sensing crosstalk between the LRI and LT, a parallel Lyot interferometer structure is also proposed. The proposed WFDSPCF sensor is expected to have potential use in biochemical sensing, measurement science, and environmental monitoring.

Non-destructive ultrasonic measurement of residual stress in metallic materials

<p>The relationship between the applied stress σ, and the measured shear wave birefringence <b>B</b> was measured in the laboratory for several low alloy steel. The birefringence response was measured with a dual polarization electromagnetic transducer comparing the time of flight for the two polarizations, in the rolling direction and the transverse direction. This stress-birefringence relationship showed a linear dependence and can be described with the relation σ = <b>K</b> * <b>B</b> + σ<sub>0</sub>. The slope of this relationship when applying a tensile stress in the transverse direction of the sample, <b>K</b>, was measured to − 1280 MPa/<b>B</b>(%) and was independent of material chemistry, whereas the position/offset of the curves, i.e., σ<sub>0</sub> , varied in between steel grades, assumed to be due to microstructural texture. A non-contact EMAT probe has been installed in a levelling mill at SSAB Special Steel in Oxelösund, Sweden, to measure the residual stress dependence on the levelling process, in daily production of steel plates. The EMAT probe has been provided by Nordinkraft AG, Remchingen, Germany. This single EMAT probe has been applied along the centerline of plates. Measurements have been made on more than 2000 plates. The responsive or reactive residual stress was successfully measured and calculated for all plates using the above stress-birefringence relationship, showing typical residual stress difference values on the production plates after levelling in the range of less than ± 100 MPa.

Strong terahertz pulse induced Pockels and Kerr effect in crystalline quartz for ultrafast pulse switching

Ultrafast pulse switching is one of the key elements for ultrahigh speed communication technology. We study the terahertz (THz) induced birefringence response on the laser pulse through the quartz with different THz electric field strength. The magnitude of the observed Pockels signals scales linearly with the THz field amplitude, while the Kerr signals scale quadratically with the THz field amplitude. We demonstrate that the quartz is a good candidate for polarization modulation of 800 nm laser pulse, which has the advantages of low-cost, large bandgap, and negligible dispersion. Furthermore, our investigation finds application beyond ultrafast polarization switching, and the THz-induced polarization gating technique works as a tool for intense THz pulse detection.

Ultrasensitive refractive index and temperature sensor based on D-shaped photonic crystal fiber by group birefringence response in a Sagnac interferometer

In this paper, a D-shaped photonic crystal fiber (PCF) sensor based on a Sagnac interferometer is proposed, and it can achieve ultrahigh refractive index (RI) and temperature sensitivity when operating around the turning point of group birefringence (Bg). We undertake a theoretical analysis on Bg and a simulation calculation to study the sensing characteristics and obtain the optimized structure parameters of the D-shaped PCF sensor. The simulation results show that the maximum average RI sensitivities can reach 3253.33 and 15500 nm/RIU in the RI range of 1.33 to 1.35 and 1.40 to 1.42, respectively. When the temperature changes from -50 to 0 °C and 0 to 50 °C, the maximum average temperature sensitivities are up to 10.11 and 10.67 nm/°C, respectively. The proposed D-shaped PCF sensor can achieve dual-parameter sensing and has great potential for practical applications in biochemical and environmental science.

Annealing temperature-dependent induced supramolecular chiroptical response of copolymer thin films studied by pump-modulated transient circular dichroism spectroscopy

Copolymer thin films showing induced supramolecular chirality are of considerable interest for optoelectronic applications such as organic light-emitting diodes. Here, we introduce a new helicene-like chiral additive with two octyloxy substituents which displays excellent chiral induction properties in an achiral polyfluorene copolymer, leading to a circular dichroism (CD) response of up to 10,000 mdeg. This chiral inducer also displays very good thermal stability, which enables us to perform an extended study on the induced chiroptical properties of the cholesteric copolymer thin films annealed at different temperatures in the range 140–260 °C. Starting from about 180 °C, a distinct change in the morphology of the CD-active film is observed by CD microscopy, from micrometre-size granular to extended CD-active regions, where the latter ones display skewed distributions of the dissymmetry parameter gabs. Broadband Müller matrix spectroscopy finds a pronounced CD and circular birefringence (CB) response and only weak linear dichroism (LD, LD’) and linear birefringence (LB, LB’). Ultrafast transient CD spectroscopy with randomly polarised excitation reveals a clean mirror-image-type transient response, which shows a second-order decay of the S1 population due to singlet–singlet annihilation processes.

Highly anisotropic and stretchable birefringent elastomers for multicolored strain displays

The birefringent response of elastomer materials with rich polarized interference colors is promising in the field of stretchable optical areas. Increasing the accessible change number of interference colors during stretching birefringent materials is important for optical strain display. Here, we can fabricate birefringent elastomers with multicolor response of polarized interference color via compositing with highly oriented cellulose nanocrystals (CNCs), transparent one-dimensional biomass nanocrystals with excellent birefringent properties, which exhibit sensitive, reversible, and controllable changes of interference color during stretching in perpendicular to the orientation of the CNCs. Employing a layer-by-layer shearing process of CNC aqueous dispersion, solvent exchange of monomers, and in-situ polymerization, we can produce birefringent elastomers with high optical path difference (>1500 nm) due to the high birefringence (2.81 × 10−3) and high thickness (within 1 mm). In addition, the high retardation of the birefringent elastomers is conducive to more interference color changes when stretching perpendicularly to the direction of oriented CNCs. Then, we demonstrate this birefringent material capable of fabricating a polarized-optical strain display by utilizing the multicolored responses during the stretching process.

(C8H7N2O2)2[Bi2Br8]·2H2O and (C8H7N2O2)6[Bi2Cl10]Cl2·2H2O: Exploring Birefringent Crystals in Hybrid Halide Systems.

In this study, new hybrid birefringent crystals of (C8H7N2O2)2[Bi2Br8]·2H2O and (C8H7N2O2)6[Bi2Cl10]Cl2·2H2O were successfully synthesized by introducing a new birefringent group [C8H7N2O2]+ by a simple aqueous solution evaporation method. They crystallize in the P21/n space group, and their structure consists mainly of the π-conjugated group [C8H7N2O2]+ and the octahedron centered on Bi3+. By first-principles calculations, the birefringence response comes from the [C8H7N2O2]+ group with a planar π-conjugated structure. Meanwhile, the synthesis, structure, first-principles calculations, and optical properties are reported in this paper.

Two-dimensional strain rate imaging study using a polarization camera and birefringent aqueous cellulose nanocrystal suspensions

The birefringence response of aqueous cellulose nanocrystal (CNC) suspensions in a two-dimensional laminar flow is measured and studied. The suspensions have CNC concentrations of 1.0 wt% (weight percentage) and 1.2 wt%. Cellulose nanocrystals are optically anisotropic rod-like particles that align when subjected to local velocity gradients, whereas at rest, they remain randomly orientated by Brownian motion. The alignment causes birefringence, a phenomenon also known as flow-induced birefringence. We study the flow through an additively manufactured flow channel and measure the amount of birefringence as well as the position of the refractive index axes by using polarizers and a polarization camera. With the help of reference data published in a previous study (Lane, Rode, et al., 2022a), strain rates are derived from the birefringence measurements and compared with numerical simulations. Two flow situations are studied, a plane Poiseuille flow and the flow around a cosine-shaped constriction. The experimentally derived shear rates for the plane Poiseuille flow are consistent with theoretical and computational results. The derived strain rates for the flow around the cosine-shaped constriction show an unexpected asymmetric profile, with the strain rates in the contraction zone being larger than in the expansion zone. The averaged orientation of the CNCs in the flow is linked to the position of the refractive index axes. In the contraction zone, the CNCs tend to align parallel to the flow, whereas in the expansion zone, the CNCs tend to align perpendicular to the flow. The results of this study are discussed in the context of previous, similar studies. The asymmetric strain rate profile around the cosine-shaped constriction is thought to originate from history effects, and the alignment of the CNCs is influenced by extensional rates.

Birefringent optical responses of single-chirality carbon nanotube membranes

Membranes composed of single-walled carbon nanotubes (SWCNTs) with a specific chiral structure (chirality) possess unique optical properties dominated by thermally robust quasi-one-dimensional excitons. Therefore they have emerged as promising materials for photonic and/or thermo-optic applications. As SWCNTs in the membranes are usually aligned two-dimensionally in a plane, and the optical responses of individual SWCNTs are highly anisotropic, the macroscopic responses of membranes are expected to depend on the light-propagation direction. However, the complex refractive-index spectra of some membrane axes are unknown, hindering the optical design of SWCNT-based devices that respond to arbitrarily propagating light. Here, we report the anisotropic complex refractive index spectra of a single-chirality SWCNT membrane fabricated via vacuum filtration. The polarization- and angle-resolved reflection spectra were obtained in the near-infrared-to-visible region. All spectral features in different polarizations and incident angle configurations were consistent with a uniaxial birefringent membrane, reflecting the random in-plane orientations of the SWCNTs. The ordinary (in-plane) refractive index spectra presented a series of sharp resonances of parallel-polarized excitons. The extraordinary (out-of-plane) refractive index in the 0.8–2.4 eV range was determined as ∼1.9. The extraordinary spectra included small but indispensable contributions from the cross-polarized exciton resonance, which are necessary for properly predicting the angle-dependent optical responses of the membrane. By completely unveiling the birefringent optical responses of single-chirality SWCNT membranes, this work paves the way for integrating SWNCT membranes into precise and diverse photonic and/or thermo-optic devices.

Graphene oxide integrated polarization maintaining microfiber refractometer based on effective birefringence response

Graphene oxide integrated polarization maintaining microfiber refractometer based on effective birefringence response

Rapid in situ quantification of rheo-optic evolution for cellulose spinning in ionic solvents

It is critical to monitor the structural evolution of complex fluids for optimal manufacturing performance, including textile spinning. However, in situ measurements in a textile-spinning process suffer from the paucity of non-destructive instruments and interpretations of the measured data. In this work, kinetic and rheo-optic properties of a cellulose/ionic liquid solution are measured simultaneously while fibers are regenerated in aqueous media from a model wet-spinning process via a customized polarized microscope. This system enables to capture key geometrical and structural information of the fiber under spinning at varying draw ratios and residence time, including the flow kinematics extracted from feature tracking, and the flow-induced morphology and birefringent responses. A physics-oriented rheological model is applied to connect the kinematic and structural measurements in a wet-spinning process incorporating both shear and extensional flows. The birefringent responses of fibers under coagulation are compared with an orientation factor incorporated in the constitutive model, from which a superposed structure-optic relationship under varying spinning conditions is identified. Such structural characterizations inferred from the flow dynamics of spinning dopes exhibit strong connections with the mechanical properties of the fully-regenerated fibers, thus enabling to predict the spinning performance in a non-destructive protocol.

Ba4 (S2 )][ZnGa4 S10 ]: Design of an Unprecedented Infrared Nonlinear Salt-Inclusion Chalcogenide with Disulfide-Bonds.

Salt-inclusion chalcogenides (SICs) have been receiving widespread attention due to their large second harmonic generation (SHG) responses and wide bandgaps, however most of them suffer from small birefringence limiting their technical application. Herein, by introducing the π-conjugated (S2 )2- units in the ionic guest of salt-inclusion structure, the first disulfide-bond-containing SIC, [Ba4 (S2 )][ZnGa4 S10 ] has been synthesized. It exhibits the widest bandgap up to 3.39eV among polychalcogenides and strong SHG response as large as that of AgGaS2 (AGS). Importantly, its birefringence reaches a max value of 0.053@1064nm among AGS-like SICs, indicating it is a promising IR nonlinear optical (NLO) material. Theoretical calculations reveal that the π-conjugated (S2 )2- units and covalent GaS layers favor the enhanced birefringence and large SHG response. This work provides not only a new type of SIC for the first time, but also new lights on the design of IR NLO materials.

Theoretical Prediction‐Assisted Synthesis and Characterization of Infrared Nonlinear Optical Material NaSrBS3

AbstractNaSrBS3, the first noncentrosymmetric alkali and alkaline earth metal mixed thioborate with the isolated [BS3] as the building units, has been synthesized successfully under the guidance of theoretical prediction. Comprehensive characterizations reveal that NaSrBS3 exhibits wide bandgap (3.94 eV), large birefringence (0.185 at 1064 nm), a high laser‐induced damage threshold (9 × AGS), and a suitable phase‐matching second‐harmonic generation (SHG) response (0.3 × AGS). Structure‐properties analyses illustrate that the [BS3] units determine the bandgap and contribute the most to the birefringence and SHG response. This work is the first successful case of “prediction to synthesis” involving infrared (IR) nonlinear optical (NLO) crystals in the thioborate system and provides an avenue to SHG materials design.

Arbitrary Achromatic Polarization Control with Reconfigurable Metasurface Systems

AbstractDynamic control over the polarization state of light is foundational for many scientific and technological applications, yet it remains a challenge to dynamically tailor responses with arbitrary polarization bases over a broad bandwidth. Broadband metasurface systems that utilize microscale displacements between two metasurfaces to enable reconfigurable polarization responses within a predefined polarization basis are reported. The metasurface pairs form an interferometer, and the lateral displacements produce detour phase shifts within the interferometer beam paths that mediate polarization state tuning. It is shown how the metasurface systems can be designed using freeform topology optimization to enable tailorable elliptical birefringence responses over a large bandwidth and how cascaded metasurface systems can enable the mapping of input and output polarization states between any two points on the Poincare sphere. It is anticipated that these concepts will have utility in imaging, display, communications, and metrology applications in classical and quantum optical domains.

The induced polarization enhanced birefringence in AlPS4 family: A first-principles investigation

As an important infrared nonlinear optical compound, metal-sulfur compounds have been widely used in various advanced optical systems. In this paper, the electronic structures, optical properties, and polarization under different external electronic field of AlPS4 (I222, P222,P4¯2c) compounds have been investigated using the first-principles method. The obtained results show that all these compounds have relatively large birefringence which are 0.256, 0.096, and 0.079@1064 nm, respectively. The relatively large birefringence has relation with the induced polarization under external electronic field rather than distorted polyhedron and spontaneous dipole moment. Both AlS4 and PS4 tetragonal give main contribution to the birefringence and second harmonic generation response.

Photothermally Induced Birefringence in an Optical Nanofiber for All‐Optical Polarization Manipulation

AbstractThis study reports the experimental observation of photothermally induced birefringence (PIB) in an optical nanofiber (NF). The PIB originates from the interaction between the azimuthally asymmetric evanescent field of a guided pump beam in mode and the gas molecules surrounding the NF. Light absorption of gas molecules results in azimuthal inhomogeneity in gas density, which induces birefringence of the NF waveguide. The swift heat transfer and molecular transportation in sub‐micrometer scale accounts for the fast response of the PIB with a measured rising and falling time within 9 and 70 ns, respectively. With a 12‐mm‐long NF, phase retardance as large as 3π is achieved. A theoretical model based on the rate equation is also developed for studying the photothermal dynamics and gas kinetics in PIB generation. This novel model is well consolidated by the numerical simulations, with the results agreeing well with the experiments. In consideration of the extremely low insertion loss, fast response, and reconfigurable principal axes of birefringence, the PIB can be used for all‐optical polarization manipulation. In addition, NF with PIB can also be an interesting platform for studies of gas–surface interaction, light–sound interaction controlling, sub‐micrometer scale heat and mass transfer, and molecular spectroscopy.

Tailoring chiral optical properties by femtosecond laser direct writing in silica

An object that possesses chirality, that is, having its mirror image not overlayed on itself by rotation and translation, can provide a different optical response to a left- or right-handed circular polarized light. Chiral nanostructures may exhibit polarization-selective optical properties that can be controlled for micro-to-nano optical element engineering. An attractive way to induce such complex nanostructures in three-dimension in glass is femtosecond laser direct writing. However, the mechanism of femtosecond laser induced chirality remains to be unveiled due to complex physical and chemical processes occurring during the ultrashort light-matter interaction. Here, a phenomenological model is proposed and is built on two-layers phase shifters to account for this laser-induced optical chirality in an initially achiral material (silica glass). This model is based on the observation that femtosecond laser induced nanogratings own two principal contributions to its aggregate birefringent response: a form and a stress-related one. By refining this formalism, a multilayer approach is developed to imprint on demand optical rotation. Values up to +/-60° at 550 nm within an optimal 80 μm thickness in silica glass are possible, corresponding to the highest value in a glass to date. These results provide new insights of circular-optical control in micro-nano optical manufacturing and open new opportunities for photonics applications.

Recent progress in borate-based short-wavelength nonlinear optical crystals with boron–oxygen skeleton modification

Recent progress and prospects of borate-based short-wavelength NLO crystals with modified boron-oxygen skeleton have been surveyed and analyzed focusing on the crystal structure features, cutoff edges, birefringence and SHG responses.

A0.5H2C6N7O3·4H2O (A = Ca2+, Sr2+) iso-cyamelurates with ultra-large π-conjugated group and excellent nonlinear optical properties

Two isocyamelurates of A0.5H2C6N7O3·4H2O (A= Ca2+, Sr2+) were successfully synthesized. Both of them showed excellent properties of wide band gap, large birefringence, and strong second order harmonic generation response.