Δn Values Research Articles

Photosensitivity of sol–gel derived inorganic xB2O3 : 20GeO2 : (80 − x)SiO2 system with various boron concentrations

Optical properties of sol–gel synthesized boron co-doped germanosilicate(xB2O3 : 20GeO2 : (80 − x)SiO2) thin films (single layer) were investigated by varying the molar concentration of B2O3 for x = 5, 10 and 20 under various annealing temperatures, ranging from 500 to 1000 °C. Densification of the thin film was found to be influenced by the concentration of boron under various annealing temperatures. Iterative deposition of the dense xB2O3 : 20GeO2 : (80 − x)SiO2 (for x = 5, 10 and 20) thin film was used to fabricate a few micrometre thick single-mode slab waveguides at 1.55 µm. Refractive indices and the propagation loss values of the waveguide samples were determined by using the prism-coupler technique. Under ultra-violet illumination, the refractive index change (Δn) of the xB2O3 : 20GeO2 : (80 − x)SiO2 increases with increasing B2O3concentration, for both transverse electric and transverse magnetic. The values of ΔnTE are ∼0.009, ∼0.012 and ∼0.014, for x = 5, 10 and 20, respectively. The high values of Δn, which increase with the B2O3 concentration are probably caused by the larger stress present in the boron doped films.

Three-dimensional birefringence imaging with a microscope tilting-stage. I. Uniaxial crystals

The development of a microscope tilting-stage suitable for use with birefringence imaging is described, thus enabling precise three-dimensional birefringence information of uniaxial crystals to be obtained. Equations have been derived for uniaxial crystals in any orientation. The technique enables precise values of the birefringence Δn=ne−no(difference between extraordinary and ordinary refractive index) and orientation of the optic axis to be obtained. The sign of the optical indicatrix may be unambiguously identified. The method is also able to obtain information on preferred orientation in a polycrystalline material. In addition to this, an unknown crystalline material may be identified, or at least classified within a specific group of crystalline materials.

Liquid crystalline perfluoroazomethines and perfluoropropenes exhibiting large dielectric anisotropies

Novel liquid crystalline compounds containing phenylperfluoroazomethine and cyclohexylperfluoropropene moieties have been synthesized. The perfluoroazomethine compounds exhibited large Δε values of up to 24.3, which is greater than those of the trifluorobenzene or trifluoromethoxybenzene derivatives that are used in TN‐TFT LCDs. The perfluoropropene compounds exhibited low values of Δn (0.044–0.057) as well as large Δε values (6.3–8.1), which are the properties required for reflection‐type LCDs.

Electron-impact broadening of radio recombination lines of atomic hydrogen for different Δn

In 1967 Griem gave a general formula for the electron-impact broadening of radio recombination lines, and an approximate expression for the width of the Δn = 1 lines. Here his general formula is calculated numerically for higher values of Δn, and an approximate expression is fitted to the results for Δn up to 70. It is shown that, for the lines with different n and Δn near a given frequency ν, the calculated widths increase monotonically up to n > 300. This result does not agree with the maximum found near n ≈ 200 by Bell et al (2000 Publ. Astron. Soc. Pac. 112 1236) for the astronomical sources W51 and Orion A at 6 GHz. Thus this mystery is not resolved by the present calculations.

Guano-derived deposits within the sandy cave fills of Naracoorte, South Australia

Geochemical and mineralogical data suggest that bat guano has made a major contribution to the development of several separate sedimentary layers, in the predominantly clastic sand and coarse silt deposits of the Naracoorte Caves, South Australia. A 20 cm thick group of reddish fine silt sediments located in Robertson Cave contains the phosphate minerals whitlockite and apatite, significant concentrations of SO3, P2O5, and CaO, and organic matter with low C/N ratios and highly enriched δN values. These data suggest that accumulations of bat guano and weathered cave limestone contributed significantly to the red silts formation. Sedimentary deposits located in Wet and Blanche Caves also contain horizons that exhibit increased concentrations of SO3, P2O5 and CaO, relatively lower C/N ratios and enriched δN values, suggesting that bat guano may have also contributed to their formation. Physical attributes evident for both these horizons further support this interpretation. A milky-white material that appears...

Guano-derived deposits within the sandy cave fills of Naracoorte, South Australia

Geochemical and mineralogical data suggest that bat guano has made a major contribution to the development of several separate sedimentary layers, in the predominantly clastic sand and coarse silt deposits of the Naracoorte Caves, South Australia. A 20 cm thick group of reddish fine silt sediments located in Robertson Cave contains the phosphate minerals whitlockite and apatite, significant concentrations of SO3, P2O5, and CaO, and organic matter with low C/N ratios and highly enriched δN values. These data suggest that accumulations of bat guano and weathered cave limestone contributed significantly to the red silts formation. Sedimentary deposits located in Wet and Blanche Caves also contain horizons that exhibit increased concentrations of SO3, P2O5 and CaO, relatively lower C/N ratios and enriched δN values, suggesting that bat guano may have also contributed to their formation. Physical attributes evident for both these horizons further support this interpretation. A milky-white material that appears to be whitlockite is present in the Wet Cave horizon, while similarities are identified by thin section petrography, between the Blanche Cave horizon and the guano layer in Robertson Cave. The development of such horizons relies on minimal sediment input from outside the cave system; hence their presence may serve as an indicator of periods of landscape stability in the palaeoenvironmental record.

Corrected infrared Sellmeier coefficients for gallium selenide

We have measured the room-temperature refractive indices of GaSe throughout the 0.7–1.4 and 2.4–5μm ranges using the minimum-deviation method of light through a prism with polarization either parallel (extraordinary refractive index ne) or perpendicular to the crystal optical c axis (ordinary refractive index no). The birefringence (Δn) at room temperature has been measured directly using polarized light interference fringes obtained in the transmittance from 1.73to4.97μm (three samples with thicknesses of 1108±1, 2480±1, and 2660±1μm) and in the range from 11.85–16.37μm (sample thickness of 6000±1μm). The no, ne, and Δn values determined from the positions of fringe maxima were compared to those obtained from prism measurements in the mid-IR and with previously published results which were mainly obtained by indirect methods. It was found that the prism method and interference fringe method resulted in values of no, ne, and Δn accurate to ±0.003 and ±0.006, respectively.

Piezo-optic properties of TGS crystals doped with D-serine

The effect of uniaxial mechanical pressure along the main crystallophysical axes on the principal values of birefringence Δn i in TGS crystals doped with 5% D-serine is investigated. It is ascertained that the values of Δn i are rather sensitive to the action of uniaxial stresses. The temperature shift coefficients ∂T c /∂σm are determined for the phase-transition points. The temperature and spectral dependences of the combined piezo-optic constants π im 0 are calculated. The contribution of the secondary electro-optic effect to the changes in the birefringence and the piezo-optic constants of doped crystals is determined. It is found that the piezooptic constants π 23 0 and π 12 0 have the same values, which indicates a decrease in the anisotropy of the optical indicatrix of doped crystals under the action of uniaxial stress. The optical and deformation contributions to the relaxation effect of piezo-optical birefringence in doped TGS crystals are found.

Acid-Base Interactions in Energetic Materials: I. The Hard and Soft Acids and Bases (HSAB) Principle-Insights to Reactivity and Sensitivity of Energetic Materials

The chemistry of energetic materials can be described applying acid-base reaction formalism. Addressing the HSAB concept, the number of electrons transferred, ΔN, in an acid-base reaction, allows for description and prediction of properties of composite and homogeneous materials. At first ΔN helps in estimating the rate of reaction of binary systems with either given fuel or oxidizer. Nevertheless ΔN is only a relative number thus the range of comparability remains narrow. At second ΔN can be used as a measure for the sensitivity of homogeneous explosives. The increased reactivity of hypothetical fragments to recombine in a reaction such as R3C.+.NO2=R3C−NO2 given by ΔN correlates very well with experimentally determined reduced impact sensitivity of 1,3,5-trinitrobenzene compounds. On the contrary the rising impact sensitivity of metal azides correlates with rising values of ΔN of Mn+/N3− reaction because increased reactivity, that is increased electron transfer from the azide anion to the metal cation triggers formation of the azide radical (.N3). The latter then decomposes rapidly to give dinitrogen. This increased reactivity/sensitivity of metral azides coincides with covalent bonding whereas ionic azides are relatively insensitive.

Reversible change of birefringence sign by optical and thermal processes in an azobenzene polymethacrylate

Birefringence (Δn) induced in an azobenzene polymethacrylate by combination of biphotonic and thermotropic processes has subsequently been changed in sign by room temperature illumination with linearly polarized blue light. The sign of Δn can be reversed again, by simply heating up the film to 100°C. This change of Δn between positive and negative values can be repeated several times. Besides, by appropriate choice of film thickness and blue light irradiation conditions the same absolute value for positive and negative Δn values can be obtained.

Synthesis and properties of new three-ring phenylacetylene liquid crystals containing the cyclohexyl unit

Two series of new three-ring phenylacetylene liquid crystals were synthesized and their physical properties were evaluated. These liquid crystal materials show only a nematic phase, high clearing points and good solubilities. The compounds containing two cyclohexyl rings exhibit moderate birefringence (Δn) values of around 0.14, while those containing one cyclohexyl ring show a broad nematic phase range and high Δn of around 0.33.

Biaxial Orientation Induced in a Photoaddressable Azopolymer Thin Film As Evidenced by Polarized UV−Visible, Infrared, and Raman Spectra

The main goal of this spectroscopic study was to obtain relevant information about the symmetry properties for a thin film of a new class of photoaddressable azopolymers, which are known to display a huge birefringence (Δn exceeding −0.45 at 632.8 nm) and a high stability and are attractive materials for rewritable recording media and optical memories. First, various real-time birefringence experiments are performed using a linearly polarized irradiation at 532.0 nm and probing the thin film sample at 675.0 nm to confirm the largest Δn values ever reported for such amorphous polymers. Then, polarized transmission measurements in the UV−visible and mid-infrared spectral ranges are compared for an isotropic and anisotropic sample. They provide strong evidences for cooperative orientational effects and for the establishment of a biaxial symmetry; the two average orientation factors 〈F2,0〉 and 〈F2,2〉 are thus extracted from infrared data for several vibrational modes. The remaining and related fourth rank factors, namely 〈F4,0〉, 〈F4,2〉 and 〈F4,4〉, are then determined from the confocal micro-Raman spectra recorded under various polarization configurations, more precisely from the two Raman intensity ratios, R1 = IXY/IXX and R2 = IYX/IYY. Reasonable values of the different orientation order parameters are thus obtained allowing to determine the overall orientation distribution function of the chromophores, in particular for the ω(CC) ring (8a) vibrational mode at 1599 cm-1. Definitive conclusions are thus drawn about the effective biaxial symmetry in this copolymer sample.

Dielectronic Recombination Rate Coefficients for H‐like through Ne‐like Isosequences of Mg, Si, S, Ar, Ca, Fe, and Ni

We present distorted-wave calculations and analytic fits to the dielectronic recombination (DR) rate coefficients of H-like to Ne-like isosequences of seven abundant astrophysical elements, including Mg, Si, S, Ar, Ca, Fe, and Ni. Both ΔN = 0 (low-temperature) and ΔN > 0 (high-temperature) DR channels are included for L-shell ions. Values of ΔN > 0 DR for less abundant ions between Mg and Ni are also obtained through interpolation along the isosequences. Interpolation is not performed for ΔN = 0 DR, since such rate coefficients are not smooth along the isosequences in general. Comparison is made with existing theoretical and experimental results, and collisional ionization equilibria resulting from the current DR rate coefficients are presented.

Kerr Effect of Xanthan/DTAB Aqueous Solutions

The Kerr effect of the Xanthan (charged polyelectrolyte; 113 ppm)/DTAB (surfactant) mixture in aqueous solution was studied. The static Kerr constant (B) and mean relaxation times (τ) values as a function of surfactant concentration (CDTAB ) were determined. The observed birefringence (Δn) is not a linear function of the electric applied field (E 2). For small E values Δn grows with E 2 and at a certain field value the birefringence tends to saturate. The addition of small quantities of DTAB lowers B values with respect to the Kerr constant of Xanthan (113 ppm) aqueous solution. The relaxation time of the mixtures is linearly dependent on the applied field and it decreases when DTAB concentration increases. The importance of the equivalent point is signalled. It is supposed that the initial rigidity of the polyelectrolite decreases because of the surfactant addition. Conductivity (σ) values as a function of surfactant concentration are presented.

Wavelength Dependence of Refractive Indices of Polyimides in Visible and Near-IR Regions

The refractive indices of eleven kinds of polyimide (PI) films formed on silicon substrates have been measured at three wavelengths (0.633, 1.320, and 1.523 µm) in the transverse electric (TE) and transverse magnetic (TM) polarization modes using the prism-coupling method. The wavelength dependence of average refractive indices was fitted using the simplified Cauchy's formula, and the estimated refractive indices at infinite wavelength (ninf) and the coefficients of wavelength dispersion (D) were determined. The PIs having higher ninf exhibit larger D, and the values of D are linearly proportional to ninf for aromatic PIs, while those of wholly alicyclic PIs are very small and deviate from the linearity. In a similar manner, the in-plane/out-of-plane birefringence (Δn) values of the aromatic PIs having higher refractive indices are large and show significant wavelength dependence, while the values of Δn of alicyclic PIs are negligible. Approximate equations are presented for aromatic PIs to estimate ninf and refractive indices at 1.320 and 1.523 µm from a refractive index at 0.633 µm.

Asymptotics for Minimal Blaschke Products and Best L1 Meromorphic Approximants of Markov Functions

Let μ be a positive Borel measure with support suppμ = E ⊂ (−1, 1) and let $$\Delta_n = {{\rm inf}\atop {{B \in {\cal B}_n}}} \int_E \mid(x)\mid^2 d\mu(x)$$ where \({\cal B}_n\) is the collection of all Blaschke products of degree n. Denote by \(B_n \in \mathcal{B}_n\) a Blaschke product that attains the value Δn. We investigate the asymptotic behavior, as n → ∞, of the minimal Blaschke products Bn in the case when the measure μ with support E = [a, b] satisfies the Szeg’o condition: $$\int_a^b {\frac{{\log \left( {{{d\mu } \mathord{\left/ {\vphantom {{d\mu } {dx}}} \right. \kern-\nulldelimiterspace} {dx}}} \right)}} {{\sqrt {(x - a)(b - x)} }}dx > - \infty .} $$ At the same time, we shall obtain results related to the convergence of best L1 approximants on the unit circle to the Markov function $$f(z) = \frac{1} {{2\pi i}}\int_E {\frac{{d\mu (x)}} {{z - x}}}$$ by meromorphic functions of the form P/Q, where P belongs to the Hardy space H1 of the unit disk and Q is a polynomial of degree at most n. We also include in an appendix a detailed treatment of a factorization theorem for Hardy spaces of the slit disk, which may be of independent interest.

Synthesis and physical properties of high birefringence phenylacetylene liquid crystals containing a cyclohexyl group

We have synthesized new phenylacetylene-based liquid crystals containing a cyclohexyl or cyclohexylethyl group and evaluated their physical properties in order to develop a range of materials having high value of birefringence. The cyclohexyl-containing compounds exhibited nematic behaviour near room temperature and moderate values of δn of around 0.3. The cyclohexylethyl-containing compounds had a very wide nematic range with a high TNI and very high values of δn of over 0.4. They also exhibited low viscosities. The order parameter was not affected by introducing either a cyclohexyl or a cyclohexylethyl group and the values of δn based on calculated polarizabilities were obtained experimentally.

High birefringence photopolymerizable phenylacetylene liquid crystals

Photopolymerizable three-ring phenylacetylene (3PA) liquid crystalline compounds were synthesized and the physical properties of the monomers and polymers were characterized in the expectation of obtaining high birefringence polymers. 3PA monomers containing acrylate substituents exhibited enantiotropic nematic phases and high δn values of around 0.35. Homogeneous alignment was retained after polymerization and high values of δn (~0.34) for the polymers were obtained. The orientation of the monomers at the photopolymerization temperature was almost fixed, such that δn and the order parameter of the polymers varied with the polymerization temperature.

Synthesis and properties of some novel high birefringence phenylacetylene liquid crystal materials with lateral substituents

We have synthesized and investigated new 3-ring phenylacetylene liquid crystals with high birefringence values (Δn) to improve the nematic temperature range while retaining a high optical anisotropy. In the case of modifying the terminal ring, the introduction of branched alkoxy chains, fluorine or methyl groups shifted the nematic phase to lower temperatures. In order to minimize the influence of the substituent on Δn, the incorporation of lateral methyl groups was chosen as the most profitable method for obtaining wide and low temperature nematic phases. With these results in mind, we studied the effect of the position of the methyl group on the physical properties. The most effective methyl position for improving the nematic temperature range was on the central ring. From the standpoint of obtaining high Δn values and low viscosity, the central ring was also the best position.

Polarization Dependence of Photoinduced Birefringence in Chalcogenide Thin Film

Polarization dependence of photoinduced birefringence has been investigated in an amorphous As–Ge–Se–S chalcogenide thin film using two 632.8 nm HeNe lasers (inducing and probing beams), which have a lower energy than the optical energy gap (EOP) of the film, that is, an exposure to sub-band gap light (hv < EOP). The polarization states of the inducing beam are controlled using a pair of phase retarder and linear polarizer to obtain linearly, circularly and elliptically polarized light beams. In addition, the kinetics of photoinduced dichroism has also been studied. The amplitudes of dichroism (D) and birefringence (Δn) increase with increasing induction time and eventually both are saturated even if their saturation times are not the same. The scalar absorption coefficient (α) of the film before photoinduction is about 6.02×103 cm-1 at 632.8 nm, that is, it is independent of polarization, but the α after photoinduction depends strongly on the polarization of the probing beam. That is, for a 0.5-µm-thick-film induced for 25 s by a laser with a power of 5.48 mW/cm2, the difference of two polarization absorption coefficients (Δα= α⊥-α∥) for the scalar α is estimated to be about 13.8%, which corresponds to D ∼4.2%. The photoinduced birefringence also depends strongly on the polarization states of the inducing beam. For example, for 0.9-µm-thick As–Ge–Se–S film the saturation values of Δn are about 0.69×10-2, 0.81×10-2, and 1.33×10-2 for the circularly, elliptically, and linearly polarized beams, respectively. In particular, the saturation values of birefringence of the film are not constant for an inducing history but vary significantly.