Negative Birefringence Research Articles

Lensing and waveguiding in birefringent double-twist cylinders demonstrated using FDTD simulations.

We demonstrate that birefringent profiles of double-twist cylinders, found in some chiral nematic systems such as blue phases, can perform as polarization-selective microlenses and waveguides in the regime of negative birefringence. Specifically, we solve Maxwell's equation using the finite-difference time-domain (FDTD) method, to simulate light propagation through double-twist cylinder birefringent structures. We show that, in case of negative material birefringence, azimuthally polarized beams experience lensing which can further be extended to waveguiding in double-twist cylinders. Lensing and waveguiding efficiency are shown to be strongly dependent on the ratio between the width of the double-twist cylinder profile and the beam width. We further characterize waveguiding in terms of losses, which are investigated in case of straight as well as curved double-twist cylinders. More generally, this work is a contribution to the design and development of (soft) birefringent profiles for optical and photonic applications.

Phase transition in BaThO3 from Pbnm to Ibmm turn the fundamental energy band gap from indirect to direct

The influence of phase transition on the electronic structure and the optical properties of BaThO3 is investigated by means of density functional theory. At room temperature BaThO3 is stable in the Pbnm phase, whereas it is stable in the Ibmm phase at high temperature. The transition from the Pbnm to the Ibmm phase cause a change in the band gap (Eg) nature from indirect to direct and a reduction by around 0.3 eV. The calculated Eg is about 4.9 eV (Pbnm) and 4.6 eV (Ibmm). The phase transition influences the k-dispersion of bands around the Fermi level and, hence, the effective masses resulting in increasing the mobility of the charge carrier and enhancing the charge transfer mechanism. The obtained optical properties clearly show the influence of phase transition on the electronic structure. It was noticed that moving from Pbnm →Ibmm phase leads to shift the whole spectral structure towards lower energies by around 0.3 eV and increase the magnitudes of the optical components. It is found that the Pbnm and Ibmm phases exhibit negative uniaxial anisotropy and negative birefringence.

59-Year-Old Man With Fatigue, Weight Loss, and Hepatomegaly

59-Year-Old Man With Fatigue, Weight Loss, and Hepatomegaly

Hybrid Polypeptide/Polylactide Copolymers with Short Phenylalanine Blocks

AbstractHybrid copolymers constituted by short l‐phenylalanine (Phe) blocks (i.e., Phen with n ranging from 2 to 25) and l‐lactide blocks of different length are synthesized and characterized. The diblock structure is obtained by ring opening polymerization of lactide using a Phe‐oligopeptide as macroinitiator. The length of the poly(l‐lactide) (PLLA) block is controlled through the [lactide]/[macroinitiator] ratio. Morphologic studies of such hybrid copolymers indicate that the assembly of PLLA can be controlled by introducing short Phe blocks. Spherulites with both positive and negative birefringence are achieved in melt crystallization as a consequence of different lamellar distributions. Instead, a high variety of structures are detected in solution‐crystallized samples. Specifically, lozenge single crystals, flower‐like crystals, fibrillar structures, compact spheres, ringed sperulites, dendritic structures, microfibers, and braid‐like microstructures are observed. Some of the detected morphologies are characteristic of self‐assembled Phe‐oligopeptides, suggesting that Phe‐blocks play a crucial role in the self‐assembly properties.

Effect of acetyl substitution on the optical anisotropy of cellulose acetate films

The effect of acetyl substitution on the optical properties of cellulose acetate (CA) was investigated in the present study, because a strong demand for advanced retardation films increases greatly these days. The hot-stretched films with high acetyl substitution had negative orientation birefringence, whereas those with low acetyl substitution had positive orientation birefringence with extraordinary wavelength dispersion. It should be noted that orientation birefringence hardly relaxed even after cessation of hot-stretching. The slow relaxation of crystal orientation was responsible for the anomalous optical anisotropy, as confirmed by two-dimensional X-ray diffraction. Moreover, the slow relaxation of orientation birefringence would greatly benefit the preparation of CA optical retardation films by hot-stretching, because it would simplify the precise control of retardation. The stress-optical coefficient in the glassy state was also evaluated, and was found to decrease with the degree of acetyl substitution. This is an attractive property for optical film applications.

Circularly polarized light to study linear magneto-optics for ferrofluids: θ-scan technique

Circularly polarized light can be divided into two vertically linearly polarized light beams with ±π/2 phase differences. In the presence of an external magnetic field, when circularly polarized light travels through a ferrofluid film, whose thickness is no more than that of λ/4 plate, magneto-optical, magnetic birefringence and dichroism effects cause the transmitted light to behave as elliptically polarized light. Using angular scan by a continuously rotating polarizer as analyzer, the angular (θ) distribution curve of relative intensity (T) corresponding to elliptically polarized light can be measured. From the T − θ curve having ellipsometry, the parameters such as the ratio of short to long axis, and angular orientation of the long axis to the vertical field direction can be obtained. Thus, magnetic birefringence and dichroism can be probed simultaneously by measuring magneto-optical, positive or negative birefringence and dichroism features from the transmission mode. The proposed method is called θ-scan technique, and can accurately determine sample stability, magnetic field direction, and cancel intrinsic light source ellipticity. This study may be helpful to further research done to ferrofluids and other similar colloidal samples with anisotropic optics.

Natural optical anisotropy of h-BN: Highest giant birefringence in a bulk crystal through the mid-infrared to ultraviolet range

The giant birefringence of layered h-BN was demonstrated by analyzing the interference patterns in reflectance and transmittance measurements in the mid-infrared to the deep ultraviolet energy range. The refractive index for polarization perpendicular to the $c$ axis is much higher than the refractive index for polarization parallel to the $c$ axis, and it displays a strong increase in the ultraviolet range that is attributed to the huge excitonic effects arising from the unique electronic structure of h-BN. Thus, h-BN is shown to exhibit a giant negative birefringence that ranges from $\ensuremath{-}0.7$ in the visible to $\ensuremath{-}2$ in the deep ultraviolet close to the band gap. The electronic dielectric constants for polarization perpendicular and parallel to the $c$ axis were determined to be ${\ensuremath{\varepsilon}}_{\ensuremath{\infty}}^{\ensuremath{\perp}}=4.95$ and ${\ensuremath{\varepsilon}}_{\ensuremath{\infty}}^{\ensuremath{\parallel}}=2.86$, respectively. The anisotropy we find in high-quality h-BN is significantly larger than proposed in previous experimental studies but in excellent agreement with ab initio calculations.

Positive and negative birefringence of materials in microwave region

We present a set of experiments with microwaves that enable one to distinguish between isotropic and anisotropic properties of wooden materials. We also determine the magnitude and the sign of the birefringence of uniaxial materials. Due to the visible structure of wood and possible direct observation of the effects on the wave propagation, solid wood boards and particle boards can be used as persuasive representatives of positively and negatively birefringent materials, respectively. Suggested experiments can easily be used for demonstration purposes or laboratory work at the undergraduate or graduate level in optics courses.

Aspiration cytopathology of tophaceous gout: a report of 22 patients

Gout may manifest with crystal-induced arthropathy and/or soft tissue tophi. Demonstration of monosodium urate (MSU) crystals is necessary to establish the diagnosis. Despite the fact that alcohol is an ideal fixative to preserve MSU crystals, very few fine-needle aspiration (FNA) cases of gout have been published. A retrospective review was performed for FNA cases diagnosed as tophaceous gout. Samples included unstained smears or smears stained with Diff-Quik or Papanicolaou stain, and formalin-fixed paraffin-embedded cell block stained with hematoxylin and eosin (H&E). We identified 22 FNA cases involving 18 men and 4 women. Only 7 patients had a clinical history of gout and 5 were taking gout medication. At least 4 patients presented with a clinical diagnosis of rule out sarcoma. All had soft tissue masses from either upper (n = 5) or lower (n = 17) extremities. Extracellular polarizing needle-shaped crystals with negative birefringence were present and visible on unstained, Diff-Quik, or Papanicolaou-stained conventional smears as well as in H&E-stained cell blocks in all cases. Our study demonstrates that MSU crystals are readily detectable under polarization on direct smears with or without staining. FNA cytology can serve as an alternative to core needle biopsy or synovial biopsy in not only confirming a diagnosis of tophaceous gout, but also in eliminating a diagnosis of soft tissue sarcoma in those patients where clinical and/or radiologic features were concerning for malignancy.

Dependence of the birefringence of polystyrene film on the stretching conditions.

We investigated the dependence of the birefringence of polystyrene (PS) film with a negative optical birefringence on the stretching conditions. We varied the stretching ratio (SR), stretching speed (SS), and stretching temperature (ST), and measured the inplane birefringence and the Nz coefficient of the PS film. The inplane birefringence was increased with greater SR and SS but decreased with greater ST. The Nz coefficient of the stretched PS film was around zero and showed similar dependence on the stretching conditions like inplane birefringence.

Electric birefringence of carbon nanotubes: Single- vs double-walled

When subjected to an external electric field, carbon nanotubes in suspension are polarized and forced to rotate due to the consequent electric torque. The analysis of this electro-orientation is interesting not only at a fundamental level, but also because of the many applications that require the alignment of these particles. Moreover, the study of the interaction of the tubes with an electric field is a highly informative non-invasive technique, able to provide much information on their microscopic properties. In order to monitor the orientation of the particles, in this work we measured the macroscopic optical anisotropy of the suspension, or electric birefringence, that emerges when the tubes are oriented by the field. Two types of particle were studied: single-walled and double-walled carbon nanotubes. The electric, optical and geometrical properties of the suspended tubes were analysed via the field dependence of the electric birefringence over a wide range. Remarkably, it was found that, whilst single-walled carbon nanotubes show a positive signal, double-walled carbon nanotubes exhibit a negative birefringence caused by an anomalous optical anisotropy.

Chiral supramolecular order revealed during the formation of calf thymus and phage DNA crystals

The control of DNA packaging has been reported to be dependent on an ordered liquid-crystalline state. However, the textural characteristics that are typical of crystals and that resemble mesophases have not been reported for highly polymerized or even shorter types of DNA filaments under in vitro conditions that favor crystallization. Because DNA crystals are expected to exhibit particular textural optical anisotropies, pure and highly polymerized calf thymus DNA and simpler λ phage DNA were crystallized from solution drops and were analyzed using high-performance polarization microscopy with and without differential interference contrast (DIC) optics. Both types of DNA formed crystals that exhibited chiral supramolecular textures resembling the twist-grain boundary (TGB) columnar mesophases described for liquid crystals and exhibited intrinsic negative birefringence. To the best of our knowledge, this is the first observation using polarization/interference optics of pure DNA crystals that have TGB columnar mesophase-like textural characteristics. A comparison of the crystals formed from the highly polymerized calf thymus DNA and those formed from the shorter phage DNA strands revealed textural differences. Compared to the phage DNA crystals, the crystals of highly polymerized thymus DNA exhibited a more intertwisted columnar distribution and a fibrous texture between their columnar structures. In addition, a form birefringence phenomenon was detected only in the thymus DNA crystals. These characteristics are presumed to reflect the higher level of supramolecular order, self-assembly and chirality in highly polymerized calf thymus DNA crystals relative to that of crystals formed from the simpler, shorter, λ phage DNA. The higher-order supramolecular organization revealed here for in vitro DNA preparations raises the possibility that this structure could also occur, possibly to a smaller degree, during DNA self-aggregation under specific in vivo conditions. Whether the DNA crystal properties presently described play a role in the establishment of higher–order levels of hierarchical chromatin structure and consequently in chromatin physiology, should be further investigated.

Bilateral olecranon bursitis – A rare clinical presentation of gout

BackgroundGout is the most common form of crystal arthropathy. Monoarthritis affecting the first metatarsophalangeal joint is the common initial presentation. Bilateral olecranon bursitis is a rare presentation of gout. Aim of the workTo describe the clinical features of bilateral olecranon bursitis as an initial presentation of gout. Case reportA 62-year old male patient presented to the rheumatology clinic , Adnan Menderes University with sudden bilateral elbow pain and swelling for three months . Swellings gradually increased to the size of a golf ball with minimal restriction in the elbow extension (170°). He didn’t have arthritis in the elbows. The patient had medical history of heart failure and chronic obstructive pulmonary disease and medications received included acetylsalicylic acid and diuretics. Blood tests revealed elevated serum uric acid (12.6mg/dL), with normal renal function tests, erythrocyte sedimentation rate (ESR) 43mm/h and C-reactive protein (CRP) 8.8mg/L. Rheumatoid factor and hepatitis markers were negative. Diagnostic bursal aspiration excluded septic bursitis and under polarized microscopy monosodium urate (MSU) crystals were identified with typical negative birefringence. A diagnosis of gout was established. ESR and CRP were normalized after diclofenac potassium (100mg) and colchicine (1.5mg). Allopurinol 300mg was added when his joint pain was relieved. ConclusionThis is the first gout case initially presenting with bilateral olecranon bursitis. Bursal fluid analysis is important in such atypical presentation to look for MSU crystals and establish a diagnosis.

Three dimensional birefringence control using nanoparticles for uniaxially oriented films

In uniaxially stretched films, the refractive indices perpendicular to the stretching direction have the same value, and so, the out-of-plane birefringence is half that of the in-plane birefringence. This means that these values cannot be controlled independently in uniaxially stretched films. The same relationship was previously observed when needle-shaped nanoparticles were added to uniaxially stretched films. This paper presents a method to achieve the three-dimensional birefringence control of uniaxially stretched films. When we added plate-shaped smectite nanoparticles to uniaxially stretched films, different relationships were observed for the in- and out-of-plane birefringence. The magnitude of the out-of-plane birefringence increased more than would be expected according to the usual relationship. According to our results, uniaxially stretched films with no out-of-plane birefringence and negative in-plane birefringence can be formed by adding smectite nanoparticles to polymer films with negative in-plane birefringence. Using our method, the three-dimensional birefringence of uniaxial polymers can be controlled, and the possibility of the uniaxial films could be drastically extended.

Single‐layered retardation films with negative wavelength dispersion birefringence made from liquid‐crystalline monomers

AbstractOrganic light‐emitting diode displays have a cathode composed of a layer of highly reflective metal. Reflection of external light from this layer can be suppressed with a broadband quarter‐wave plate. Although various types of quarter‐wave plate retardation films have been prepared by copolymerizing, mixing, or laminating multiple polymers, ideal wavelength dispersion has not been achieved with thin retardation films because of their relatively low birefringence and the complexity of the procedure required manufacturing them. In this study, we developed (i) new liquid‐crystalline monomers with negative wavelength dispersion birefringence that we used to obtain thin, single‐layered retardation films suitable for coating and (ii) retardation films with different molecular alignments. We found that the monomers showed high solubility and high regularity of molecular alignment, with less damage to the substrate and alignment films. We also investigated the wavelength dispersion and thermal stability of the films. We succeeded in developing retardation films that had a homeotropic alignment or a hybrid alignment with negative wavelength dispersion. These alignments can be used to obtain antireflection films with an improved viewing angle for organic light‐emitting diode displays or next‐generation thin displays.

P‐159: Wide Viewing Angle Negative Dispersion Retarder by Stacking Reactive Mesogen with a Positive Birefringence on Stretched Film with a Negative Birefringence

We reported a wide viewing angle negative dispersion retarder film. We stacked the reactive mesogen (RM) and stretched polymethylmethacrylate (PMMA). The retardation (Re) was Re(450 nm)/ Re(550 nm) = 0.818, Re(650 nm)/ Re (550 nm) = 1.110. The out‐of‐plane retardation (Rth) was 6 nm. This value is much smaller than a general retarder and exhibits wide viewing angle property.

Wavelength dispersion of birefringence of oriented polyethylene films.

Oriented polyethylene films, in which stacked lamellae grow perpendicular to the flow direction, can show extraordinary wavelength dispersion of birefringence; i.e., birefringence increases with wavelength. Owing to the periodical change of the refractive indices between the crystalline and amorphous layers along the flow direction, with oriented long lamellae having a high refractive index, the form birefringence has negative values. Furthermore, the refractive indices of the crystalline region show a stronger wavelength dependence than those of the amorphous region, which is responsible for the marked wavelength dispersion in the form birefringence. The combination of negative form birefringence with strong wavelength dispersion and positive orientation birefringence can give extraordinary wavelength dispersion.

Spin-polarized Second Harmonic Generation from the Antiferromagnetic CaCoSO Single Crystal

The spin-polarized second harmonic generation (SHG) of the recently synthesized CaCoSO single crystal is performed based on the calculated electronic band structure. The calculation reveals that the spin-up (↑) channel of CaCoSO possesses a direct energy gap (Γv-Γc) of about 2.187 eV, 1.187 eV (Kv-Kc) for the spin-down (↓) channel and an indirect gap (Γv-Kc) of about 0.4 eV for the spin-polarized CaCoSO single crystal. The linear optical properties obtained reveal that the recently synthesized crystal exhibits considerable anisotropy with negative uniaxial anisotropy and birefringence favor to enhance the SHG. We have calculated the three non-zero tensor components of the SHG and found the is the dominat component, one with a large SHG of about (d33 = 6.936 pm/V at λ = 1064 nm), the half value of KTiOPO4 (KTP). As the values of (↑) < (↓) < spin-polarized are related to the values of the energy gap of (↑) 2.187 eV> (↓) 1.187 eV> spin-polarized gap 0.4 eV; therefore, a smaller energy gap gives better SHG performance. Furthermore, the microscopic first hyperpolarizability, βijk, is calculated.

Birefringence-Induced Modulation of Optical Activity in Chiral Plasmonic Helical Arrays

Chiral nanomaterials are characterized by handedness morphology on the nanoscale, manifested as preferential interaction with circularly polarized light. However, the origin of this light-matter interaction remains elusive. Here we simulated a model of chiral helical arrays of plasmonic nanoparticles with central anisotropic nanopillars to examine the effect of birefringence on the collective chiroptical response. Contrary to typical assumptions in previous works, we varied the biaxial refractive indices of the central nanopillars and observed a significant modulation of optical activity by calculating and characterizing circular dichroism (CD) spectra. The chiroptical response exhibited a sign change compared with that of the isotropic condition in a specific parametric range of negative birefringence. In addition, the CD peak increased by 3 to 16 as the ordinary refractive index increased from 1.5 to 3.0. These results are likely to be useful for designing chiral nanomaterials for applications in metamaterials, biosensors, and optoelectrical devices.

Mechano-optical behavior of loosely crosslinked double-network hydrogels: Modeling and real-time birefringence measurement during uniaxial extension

Real-time uniaxial strain-induced birefringence in loosely crosslinked double-network (DN) hydrogels synthesized from acrylamide (AAm) and N,N-dimethyl(acrylamide) (DMA) was measured. Tensile tests were performed at different extension rates from quasi-static conditions to very rapid tests followed by a holding for relaxation. Both DN hydrogels exhibited negative birefringence whose absolute value increased with extension and remained constant during relaxation. DN hydrogel synthesized from AAm displayed a linear stress optical (birefringence – true stress) behavior, however, a nonlinear trend was observed for the DN gel synthesized from DMA. A simple photoelastic model was developed based on the mechanical behavior of the gels using Fung elastic potential and Brewster's stress-optical law, and the model was compared with the experimental data.