Birefringence Δn Research Articles

High-Performance Birefringence of Periodic Nanostructures in FTO Thin Film Fabricated by IR-UV Femtosecond Laser

By using infrared to ultraviolet (IR-UV) femtosecond laser directing, periodic nanostructures were efficiently fabricated on an F-doped tin oxide (FTO) film with a thickness of 650 nm. The morphology of the nanostructures and duty cycle were studied in detail by changing the laser fluence and scanning speed, where three lasers with central wavelengths of 343, 515, and 1,030 nm were used in the experiments. Under the 515 nm laser irradiation with scanning speed of 0.01 mm/s and laser fluence of 23 mJ/cm2, the periods Λ is 172 nm, the ablated nanogroove with width w2 is 52 nm, the birefringence Δn reached a maximum of 0.21, and the phase retardance was up to 135 nm. The morphology of the nanostructures and the birefringence effects of the FTO film prepared by a femtosecond laser at wavelengths of 1,030 and 343 nm were also studied, where the phase retardance of the nanostructured FTO film was much lesser than for the 515 nm laser because the thickness of the nanoripples layer, and, thus, the duty cycle of periodic nanoripples was smaller. Finally, a large-area FTO film with periodic nanostructures was fabricated efficiently by direct laser writing using a 515 nm fs laser beam focused via a cylindrical lens, and demonstrated the characteristics of a quarter-wave plate for 532 nm light.

Design of a diamond-like infrared nonlinear optical material LiBS2 with ultra-wide band gap

The exploration of new infrared (IR) nonlinear optical (NLO) materials with large second-harmonic generation (SHG) responses and wide band gap (Eg) is an urgent need but challenging. Starting from the superior unit combination strategy and considering the advantages of borates, chalcogenides and Li elements, we have focused our attention on the exploration of IR NLO materials in the Li-based thioborates. Four novel non-centrosymmetric LiBS2 structures, were obtained successfully through crystal structure prediction by analogy and structural optimization based on the thermodynamic and dynamic stability analysis. Among them, LiBS2-I exhibits an ultra-wide band gap Eg = 4.4 eV, moderate SHG response 0.6 × AgGaS2, and suitable birefringence Δn = 0.04 at 1064 nm, which satisfies the good balance between Eg ≥ 3.0 eV and dij ≥ 0.5 × AgGaS2. The role of microscopic units [BS4] in NLO effect was investigated. This work enriches the structural diversity of thioborates and provides a new approach to the exploration of excellent IR NLO materials.

Opto-Thermo-Mechanical Characterization of Crazing Phenomena Observed for Isotactic Polypropylene Fibers Using Digital Photoelasticity and the Computed Tomography Techniques

Digital photoelasticity was used to characterize the crazing phenomena of isotactic polypropylene (iPP) fibers as a precursor of fracture processes. In this study, the effect of stretching at different rates on the formation of crazes was investigated for the iPP fibers. Also, the influence of drawing the iPP fibers at different temperatures on the formation of the crazes was studied. In addition, the effect of heating the crazed iPP fibers on the formed crazes was characterized using digital photoelasticity. Computed tomography was used to obtain qualitative and quantitative measurements of the crazes densities along the cross-sections of the iPP fibers. Also, the birefringence (Δn) values of the crazes were measured for different conditions of stretching and temperature and compared to the Δn of the bulk material. The photoelastic patterns of the iPP fibers are given for illustrating the crazes behavior in the iPP fibers.

Designing A New Infrared Nonlinear Optical Material, β‐BaGa2Se4 Inspired by the Phase Transition of the BaB2O4 (BBO) Crystal

AbstractInfrared nonlinear optical (IR NLO) crystals play a significant role in the development of IR laser technology. But rationally designing a new IR NLO crystal remains a huge challenge because of the unpredictability of inorganic structures. Herein, inspired by phase transformation of the famous BaB2O4 (BBO) crystal, a temperature‐induced centrosymmetric (CS) to noncentrosymmetric (NCS) transformation approach is employed in CS BaGa2Se4 to uncover a new NCS ternary chalcogenide, β‐BaGa2Se4 which can exhibit the well‐balanced NLO properties, including moderate phase‐matching SHG response (≈0.6×AgGaS2), high LDT (10×AgGaS2), and large birefringence (Δn=0.18 in the visible region). Therefore, β‐BaGa2Se4 will be a promising IR NLO crystal. The analysis for the structure‐property relationship shows that the excellent NLO properties of β‐BaGa2Se4 mainly originate from edge‐sharing GaSe4 tetrahedral chains, which are different from B3O6 groups in β‐BBO and respect a new direction for the design of IR NLO crystals. So, we believe that the current research provides not only a new IR NLO crystal but also some insights for the design of new IR NLO crystals.

Designing A New Infrared Nonlinear Optical Material, β-BaGa2 Se4 Inspired by the Phase Transition of the BaB2 O4 (BBO) Crystal.

Infrared nonlinear optical (IR NLO) crystals play a significant role in the development of IR laser technology. But rationally designing a new IR NLO crystal remains a huge challenge because of the unpredictability of inorganic structures. Herein, inspired by phase transformation of the famous BaB2 O4 (BBO) crystal, a temperature-induced centrosymmetric (CS) to noncentrosymmetric (NCS) transformation approach is employed in CS BaGa2 Se4 to uncover a new NCS ternary chalcogenide, β-BaGa2 Se4 which can exhibit the well-balanced NLO properties, including moderate phase-matching SHG response (≈0.6×AgGaS2 ), high LDT (10×AgGaS2 ), and large birefringence (Δn=0.18 in the visible region). Therefore, β-BaGa2 Se4 will be a promising IR NLO crystal. The analysis for the structure-property relationship shows that the excellent NLO properties of β-BaGa2 Se4 mainly originate from edge-sharing GaSe4 tetrahedral chains, which are different from B3 O6 groups in β-BBO and respect a new direction for the design of IR NLO crystals. So, we believe that the current research provides not only a new IR NLO crystal but also some insights for the design of new IR NLO crystals.

Millimetre-wave range optical properties of BIBO

We present the thorough studies of optical properties of BiB3O6 (BIBO) crystal in the millimeter-wave (subterahertz) range. We observe a large birefringence Δn = nZ -nX = 1.5 and the values of absorption coefficients of all three axes to be less than 0.5 cm−1 at the frequency of 0.3 THz. The difference from visible range in angle ϕ between the dielectric axis z and crystallophysical axis X is found to be more than 6°. The simulated phase-matching curves in the xz plane of the crystal show the optimal value of the angle θ to be around 25.5°±1° for an efficient millimeter-wave generation under the pump of 1064 nm laser radiation.

Optical refracting properties, birefringence and order parameter in mixtures of liquid crystals: Direct smectic A – Isotropic and reverse isotropic – Smectic A phase transitions

Due to the physical anisotropic and self-assembling nature, liquid crystalline materials holdvery important place in theoretical, experimental and applied physics. Besides, liquid crystals are important materials as working and active elements in various technical devices, optical and optoelectronic systems and technological processes.In this work investigations of the thermo-optical properties of the monomorphic smectogens are presented. Homogeneous binary mixtures of 4-n-alkyl-4′-cyanobiphenyl mesogens were objects in these investigations. The optical refracting and birefringent properties, and behavior of the order parameter at the direct smectic A – isotropic and reverse isotropic – smectic A phase transitions are considered. Temperature dependences of the mean refracting index n, refracting indices for the ordinary no and extraordinary ne rays, and birefringence Δn have been determined. Temperature dependences of the order parameter for the heating – cooling circular cycle at phase transitions are presented.

The stability, structural, electronic, and optical properties of hydrogenated silicene under hydrostatic pressures: a first-principle study.

The structural, electronic, and optical properties of hydrogenated silicene have been studied under different hydrostatic pressures using first-principle calculations. The binding energy and band structure have been calculated for chair (C-) and boat (B-) structures, which are having good stability at 0 GPa, 3 GPa, 6 GPa, 9 GPa, 12 GPa, 15 GPa, and 18 GPa hydrostatic pressures. Stability has been verified using binding energy and phonon calculations. The C- and B-structures have become metallic and unstable at 21 GPa. The optical properties of B-configuration have been studied in the energy range of 0-20eV. Five optical parameters such as conductivity threshold (σth), dielectric constant ε(0), refractive index n(0), birefringence Δn(0), and plasmon energy (ħωp) have been calculated for the first time under different hydrostatic pressures. The calculated values are in good agreement with the reported values at 0 GPa.

Single-polarization single-mode hollow-core photonic-bandgap fiber with thin slab waveguide.

A novel single-polarization single-mode hollow-core photonic bandgap fiber with thin slab waveguide (TSW) was designed and simulated. Single-polarization guidance is achieved by the high loss of a polarized fundamental mode (FM) induced by mode coupling with a higher-order TE/TM mode of TSW and low loss of another polarized FM. We achieve a polarization loss ratio ∼ 46.9 dB, birefringence Δn ∼ 2.4 × 10-4, loss ∼ 35.9 dB/km and minimum higher-order mode extinction ratio > 15 dB. Moreover, the performance could be maintained when the guidance wavelength λ = 1.44 ∼ 1.56 µm and bending radius rc > 9 mm. The proposed model will be suitable for application as resonator sensing paths of miniaturized resonator fiber optic gyroscopes, high-performance interferometers, fiber lasers, frequency metrology, quantum communications, and laser-based gas sensing, etc.

Giant Second-Harmonic Generation Response and Large Band Gap in the Partially Fluorinated Mid-Infrared Oxide RbTeMo2O8F.

Strong second-harmonic generation (SHG) and a wide band gap are two crucial but often conflicting parameters that must be optimized for practical nonlinear optical (NLO) materials. We report herein the first d0-transition-metal (TM) tellurite with half of the d0-TM-octahedra partially fluorinated, namely, quinary RbTeMo2O8F, which exhibits giant SHG responses (27 times that of KH2PO4 (KDP) and 2.2 times that of KTiOPO4 (KTP) with 1064 and 2100 nm laser radiation, respectively), the largest SHG values among all reported metal tellurites. RbTeMo2O8F also possesses a large band gap (3.63 eV), a wide optical transparency window (0.34-5.40 μm), and a significant birefringence (Δn = 0.263 at 546 nm). Theoretical calculations and crystal structure analysis demonstrate that the outstanding SHG responses can be definitively attributed to the uniform alignment of the polarized [MoO5F]/[MoO6] octahedra and the seesaw-like [TeO4], and the consequent favorable summative polarization of the three distinct SHG-active polyhedra, both induced by partial fluorine substitution on the [MoO6] octahedra.

Be2(BO3)(IO3): The First Anion‐mixed Van der Waals Member in the KBe2BO3F2 Family with a Very Strong Second Harmonic Generation Response

AbstractTo obtain new nonlinear optical (NLO) materials with a large second harmonic generation (SHG) effect has always been a great challenge. We have synthesized the first metal borate‐iodate NLO crystal, Be2(BO3)(IO3) (BBIO), by multicomponent modification of KBe2BO3F2 (KBBF), in which the structural features of KBBF were maintained and (IO3)− groups were connected to honeycomb [Be2BO3O2]∞ layers. As the first KBBF family member with mixed anionic groups, BBIO benefited from the synergistic effect of (IO3)−, (BO3)3− and (BeO4)6− groups, and exhibited a very strong SHG response of ≈7.2×KH2PO4 (KDP, @1064 nm) and a large birefringence (Δn) of 0.172 at 1064 nm. BBIO may, unexpectedly, optimize growth habits via van der Waals forces. This study presents borate‐iodate as a new NLO material and it demonstrates opportunities in KBBF structural engineering.

Be2 (BO3 )(IO3 ): The First Anion-mixed Van der Waals Member in the KBe2 BO3 F2 Family with a Very Strong Second Harmonic Generation Response.

To obtain new nonlinear optical (NLO) materials with a large second harmonic generation (SHG) effect has always been a great challenge. We have synthesized the first metal borate-iodate NLO crystal, Be2 (BO3 )(IO3 ) (BBIO), by multicomponent modification of KBe2 BO3 F2 (KBBF), in which the structural features of KBBF were maintained and (IO3 )- groups were connected to honeycomb [Be2 BO3 O2 ]∞ layers. As the first KBBF family member with mixed anionic groups, BBIO benefited from the synergistic effect of (IO3 )- , (BO3 )3- and (BeO4 )6- groups, and exhibited a very strong SHG response of ≈7.2×KH2 PO4 (KDP, @1064 nm) and a large birefringence (Δn) of 0.172 at 1064 nm. BBIO may, unexpectedly, optimize growth habits via van der Waals forces. This study presents borate-iodate as a new NLO material and it demonstrates opportunities in KBBF structural engineering.

Exploring Deep-UV Nonlinear Optical Materials with Enhanced Second Harmonic Generation Response and Birefringence in Fluoroaluminoborate Crystals.

Deep-UV (DUV) nonlinear optical (NLO) materials are of vital importance to demanding DUV laser applications; however, those with a large NLO coefficient, wide band gap, and sufficient phase-matching ability are rare. In this work, by combining π-conjugated B3O6 groups and distort AlO3F tetrahedra, we successfully designed and synthesized two fluoroaluminoborates, RbAlB3O6F (RABF) and Cs0.5Rb0.5AlB3O6F (CRABF). In addition, the solid solution CsxRb1-xAlB3O6F (0.2 < x < 0.8) polycrystalline samples were obtained by the standard solid-state reaction. It was shown that all these compounds are NLO-active and possess short UV cutoff edges (<200 nm). Interestingly, although they have the same fundamental structural units, their crystal structures and second harmonic generation (SHG) responses are significantly different owing to the cation effect. Theoretical calculations reveal that both B3O6 and AlO3F groups contribute to the SHG responses. Remarkably, it also indicates that RABF exhibits a large birefringence (Δn = 0.0946 at 1064 nm), which is capable of realizing deep-UV phase matching down to 174 nm. The exploration of fluoroaluminoborates provides a new perspective for searching excellent deep-UV NLO materials.

Electro-Optical and Photo Stabilization Study of Nematic Ternary Mixture.

Liquid crystal materials composed of mixed nematic compounds find broad use in liquid crystal displays and photonic applications. A ternary mixture formed from three different nematic compounds shows peculiar behavior such as tunable electro-optical properties dependent on the frequency of the driving voltage. The paper presents an analysis of the response time and phase retardation of a frequency tunable nematic liquid crystal mixture (under code name 5005). This material possesses high birefringence (Δn = 0.32 at 633 nm) as well as high dielectric anisotropy (Δε = 6.3 at 100 Hz). The unique property of the 5005 mixture is frequency-controlled phase modulation, as in a dual frequency liquid crystal, while dielectric anisotropy goes to zero instead of being negative at high frequencies. For each component of the mixture, details on mesomorphic properties and their role in the formulation of the mixture are reported. The 5005 mixture was characterized by multiple investigation techniques, such as temperature dependence dielectric anisotropy, transmittance measurements image polarizing microscopy, and UV stability.

The pressure effect on stability, electronic and optical properties of fluorine passivated graphene (CF)n: A first-principle study

The structural, electronic, and optical properties of fluorinated graphene under different hydrostatic pressures and thermodynamic properties under different temperatures have been studied using first-principle calculations. The calculated binding energy and phonon dispersion show that the fluorinated graphene is stable up to 90 GPa external pressure. The behavior of energy bandgap under different pressures shows that the electronic properties of fluorinated graphene are less pressure-sensitive compared to hydrogenated graphene. The functionalization increases the electron mobility of graphene. The fluorinated graphene is more temperature-sensitive compared to hydrogenated graphene and graphene. Six important parameters: energy bandgap (Eg), binding energy (Eb), dielectric constant ε(0), refractive index n(0), birefringence Δn(0), conductivity threshold (σth) and plasmon energy (ħωp) have been reported under different pressures for the first time. The calculated values agree well with the available reported values at 0 GPa pressure.

Electro-optic characteristics investigation on NLO crystal; L-Valine doped Ethylene Diamine Tetra Acetate (EDTA) composite crystal using quantum chemical calculations

In this research work, the attempt was made to fabricate efficient NLO crystal using organic composite; L-Valine doped Ethylene Diamine Tetra Acetate (EDTA). The observed XRD peaks intimate the crystal lattice as orthorhombic and respective lattice characteristics were studied. The unit cell was calculated as a = 5.811 Å, b = 11.735 Å and c = 5.014 Å and the respective refractive indices determined to be 1.547, 1.789 and 1.610. The Birefringence (Δn) Kλ/t is found to be 0.271 and the corresponding NLO efficiency calculated to be 0.846 [I/I(SiO2)]. The compositional parts activity was keenly observed from their vibrational modes and their space charge and oriental polarization characteristics were studied and thereby dielectric susceptibility for inducing NLO activity was presented. The chemical shift for both experimental and theoretical analysis was observed and the storage of chemical potential among core C was measured. The band gap and transparency for IR and UV-Visible region estimated and the wide range for both confirmed the dielectric reactance for optical energy. The DTA-DSC curve was traced and the thermal stability and Gibbs free energy profile was studied. The SEM images recorded and the surface morphology was displayed for knowing the molecular coordination arrangement. The chemi-potential energy exchange was measured for different molecular entities for non bonding system of bonded composite.

Macroscopic and microscopic order parameters of lyotropic nematic liquid crystals by polarised light microscopy

ABSTRACT In this study, the birefringence (δn) and macroscopic order parameter (Q) of lyotropic nematic calamitic (NC) mesophase were obtained in the reentrant isotropic (IRE)–NC–isotropic (I) phase transition range by only examining its optical transmittance under a polarising microscope. Moreover, the microscopic order parameter (S) was found by obtaining absorption coefficients from these transmittances. Generally, the macroscopic order parameter was larger than the microscopic one. The difference between them was small near the IRE–NC phase transition and the maximum birefringence region whereas it was relatively high near the NC–I phase transition.

Comparing polarized Raman spectroscopy and birefringence as probes of molecular scale alignment in 3D printed thermoplastics.

Polymer chain orientation is crucial to understanding the polymer dynamics at interfaces formed during thermoplastic material extrusion additive manufacturing. The flow field and rapid cooling produced during material extrusion can result in chains which are oriented and stretched, which has implications for interdiffusion and crystallization. Polarized Raman spectroscopy offers a non-destructive and surface sensitive method to quantify chain orientation. To study orientation and alignment of chains in 3D printed polycarbonate filaments, we used a combination of polarized Raman spectroscopy and birefringence (Δn) measurements. By changing the orientation of the sample with respect to polarization of incident radiation, we probe changes in the ratio between orientation-dependent vibration modes and orientation-independent modes. We used principal component analysis (PCA) and partial least squares (PLS) regression to develop correlations for birefringence and Raman measurements in samples that were pulled at different draw ratios (DRs). PCA was used to differentiate between orientation-dependent and orientation-independent modes, while PLS regression was used to calculate birefringence from Raman measurements of 3D printed samples. Birefringence measurements were compared to the polycarbonate intrinsic birefringence of 0.2, to estimate the degree of orientation. We find that measured values of birefringence underestimate orientation compared to Raman measurements.

Introduction of 5,6-dihydro-4H-cyclopenta[b]thiophene core unit into phenyl-tolane: Expanding the mesophase range and increasing the birefringence and dielectric anisotropy of liquid crystal

ABSTRACT Six novel phenyl-tolane type liquid crystals based on 5,6-dihydro-4 H-cyclopenta[b]thiophene core were designed and synthesised by Sonogashira coupling reactions in high yields. Two reference compounds were then used to clarify the effects of this new core on the mesomorphic behaviours and physical properties of phenyl-tolane type mesogens and found that these new core-based mesogens possessed wider mesophase ranges. Both the birefringence (Δn) and dielectric anisotropy (Δε) values were increased after the employment of this new core, offering an alternative option for the design and synthesis of high-performance phenyl-tolanes. The geometry, ultraviolet absorption, polarisability (α) and dipole moment (μ) of two representative compounds and their references were calculated by density functional theory to correlate the structure–property relationship of the new mesogens. The calculated energy minimum structures of the new mesogens showed well linearity and the molecular length/width ratio was increased, which would benefit the formation of the nematic phase. The orders of the calculated polarisability (α) and dipole moment (μ) of two representative compounds and their references were in accordance with the sequences of the measured birefringence (Δn) and dielectric anisotropy (Δε) values, respectively, which might shed light on the correlation between microscopic molecular structure and macroscopic physical properties.

5.3: Invited Paper: High Efficiency Phase Modulators

In communication networks, wavelength selective switch (WSS) is one of the key components in reconfigurable optical add‐drop multiplexer (ROADM) [1]. Several technologies have been developed to achieve a high‐performance WSS, such as micro electromechanical systems (MEMS) [2], liquid crystal on silicon (LCOS) [3], arrayed waveguide grating (AWG) [4], and hybrid planar lightwave circuit (PLC)‐MEMS [5]. Among these, LCOS‐based WSS is most attractive for the next‐generation optical networks due to its controllability with individual electrical control on pixel. It shows advantages of flexible bandwidth adjustment, adaptive alignment, and robustness without mechanical movements.A LCOS exhibiting a high diffraction efficiency at a large deflection angle is demonstrated [6]. A liquid crystal (LC) mixture with a large birefringence (Δn = 0.27, at λ = 1550 nm) and a large dielectric constant (Δε = 10.4) is developed to obtain the high‐phase retardation, more than 4π, at 1550 nm within a relatively low operation voltage of 5.5 V on LCOS. When compared with the conventional modulation method of 2π phase retardation, both grating period and phase retardation are doubled in 4π modulo modulation. Using the high‐phase retardation modulation method, the LCOS may achieve high diffraction efficiency, more than 56.6% at 4.5° deflection angle of C‐band wavelength with an optimized phase retardation profile.A polarization‐independent blue phase liquid crystal on silicon (BPLCoS) device with low operation voltage for 2π phase depth is proposed [7]. With optimized reflection structure and two reflection films, the incident light may experience multifold optical path and 2π phase depth can be obtained. For the polarization‐independence, an inclined electric field made by periodical gradient voltage is applied on the blue phase liquid crystal (BPLC) to match the light propagation direction. With the structure, the operation voltage can be lowered to 5.5 V in simulation and 5.9 V in experiment for 2π phase modulation at 1550 nm.The high diffraction efficiency and polarization‐independent phase modulators show the great potential application of beam steering for the optical communication and the holographic display.