Search results for "birefringence"
showing 10 items of 133 documents
Highly transparent and birefringent chromophores for organic photorefractive materials
1999
Abstract A series of chromophores for application in organic photorefractive (PR) materials is investigated by electro-optical absorption measurements (EOAM). This experimental technique yields information on the transition dipole moment μ ag , the ground-state dipole moment μ g , and the change of the dipole moment upon optical excitation Δ μ within the intense charge transfer (CT) band of the dyes. It is shown that the results of the EOAM experiment allow us to estimate the PR figures-of-merits (FOMs) of the chromophores by either perturbational two-level equations or Kramers–Kronig transformation. In particular, chromophores based on the heterocyclic dihydropyran and dihydropyridine grou…
Nonlinear polarization effects in optical fibers: polarization attraction and modulation instability [Invited]
2014
We review polarization stabilization techniques based on the polarization attraction effect in low-birefringence fibers. Polarization attraction or pulling may be based on cross-polarization modulation, on parametric amplification, and on Raman or Brillouin scattering. We also review methods for laser frequency conversion based on polarization modulation instabilities in low- and high-birefringence fibers, and photonic crystal fibers. Polarization instabilities in nonlinear fibers may also be exploited for sensing applications.
Influence of the arrangement of the crystals and the structure of the noncrystalline regions on the mechanical properties of polyethylene terephthala…
2007
Amorphous samples of polyethylene terephthalate were stretched with different rates and stretching ratios at different temperatures. Afterwards they were crystallized. The arrangement of the crystals and the conformations of the chains in the noncrystalline regions were investigated by means of X-ray wide-angle scattering, X-ray small-angle scattering, birefringence measurements and nuclear magnetic resonance measurements. The influence of the morphological structure on the mechanical strength was determined. The stretching ratio itself generally does not characterize the orientation state. The structure obtained after crystallization depends mainly on the birefringence of the sample after …
Supramolecular hierarchy among halogen and hydrogen bond donors in light-induced surface patterning
2015
Halogen bonding, a noncovalent interaction possessing several unique features compared to the more familiar hydrogen bonding, is emerging as a powerful tool in functional materials design. Herein, we unambiguously show that one of these characteristic features, namely high directionality, renders halogen bonding the interaction of choice when developing azobenzene-containing supramolecular polymers for light-induced surface patterning. The study is conducted by using an extensive library of azobenzene molecules that differ only in terms of the bond-donor unit. We introduce a new tetrafluorophenol-containing azobenzene photoswitch capable of forming strong hydrogen bonds, and show that an io…
Polarization Insensitive Wavelength Conversion in a Low-Birefringence SiGe Waveguide
2016
We report the first demonstration of a single-pass dual-orthogonal-pump four-wave mixing-based wavelength conversion scheme in a silicon-based waveguide. The silicon germanium waveguide used was designed to exhibit strong TE/TM mode similarity across a broad wavelength range as well as a large nonlinear coefficient. A polarization-dependent loss of just 0.42 dB was measured, and the conversion of 40-Gb/s differential phase-shift keying signals was demonstrated with 1.5-dB power penalty at a bit error ratio of $10^{-9}$ .
Design of a real-time spectroscopic rotating compensator ellipsometer without systematic errors
2014
6th International Conference on Spectroscopic Ellipsometry (ICSE), Kyoto, JAPAN, MAY 26-31, 2013; International audience; We describe a spectroscopic ellipsometer in the visible domain (400-800 nm) based on a rotating compensator technology using two detectors. The classical analyzer is replaced by a fixed Rochon birefringent beamsplitter which splits the incidence light wave into two perpendicularly polarized waves, one oriented at +45 degrees and the other one at-45 degrees according to the plane of incidence. Both emergent optical signals are analyzed by two identical CCD detectors which are synchronized by an optical encoder fixed on the shaft of the step-by-step motor of the compensato…
Real time optical immunosensing with flow-through porous alumina membranes
2014
Through the presentation of analytical data from bioassay experiments, measured by polarimetry, we demonstrate for the first time a real time immunoassay within a free standing macroporous alumina membrane. The 200 nm nominal pore diameter of the membrane enables flow-through, thereby providing an ideal fluidic platform for the targeted delivery of analytes to bioreceptors immobilized on the pore walls, enabling fast sensing response times and the use of small sample volumes (<100 mu L). For the immunoassay, the pore walls were first coated with the functional copolymer, copoly(DMA-NAS) using a novel coupling process, before immobilization of the allergen protein, beta-lactoglobulin, by spo…
Theory of birefringence and spontaneous polarization in the tetragonal phase of PbTiO3 due to lattice deformation caused by the change of temperature
1995
The microscopic mechanism of birefringence in the tetragonal phase of PbTiO3 is discussed taking account of the dipole-dipole interaction (dipole-dipole effect) due to the ionic and electronic polarizations of the crystal and the spontaneous Kerr effect as a cause of the strong local field acting on the constituent ions, where the lattice deformation due to the change of temperature is also considered. For the spontaneous polarization we use only the first effect. It is found that the birefringence and the spontaneous polarization are in good agreement with the experimental data.
Natural optical anisotropy of h-BN: Highest giant birefringence in a bulk crystal through the mid-infrared to ultraviolet range
2018
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 -0.7 in the visible to -2 in the deep ultraviolet close to the band gap. The electronic dielectric constants f…
A structural comparison of halloysite nanotubes of different origin by Small-Angle Neutron Scattering (SANS) and Electric Birefringence
2018
The structure of halloysite nanotubes (Hal) from different mines was investigated by Small-Angle Neutron Scattering (SANS) and Electric Birefringence (EBR) experiments. The analysis of the SANS curves allowed us to correlate the sizes and polydispersity and the specific surfaces (obtained by a Porod analysis of the SANS data) of the nanotubes with their specific geological setting. Contrast matching measurements were performed on patch Hal (from Western Australia) in order to determine their experimental scattering length density for a more precise analysis. Further characterization of the mesoscopic structure of Hal was carried out by Electric Birefringence (EBR), which allowed to study th…