Longitudinal Dipole Research Articles

Low-frequency dielectric spectroscopy and distinct relaxation modes in smectic phases of liquid crystal dimers

Low-Frequency (LF~20 Hz–10 MHz) ac field response and relaxation modes are investigated in layered liquid crystalline (LC) smectic phases exhibited by Hydrogen bonded dimers, viz., nOnBA:MA:nOBA’s with sort spacer moiety and long flexible end chains for n = 10,11 and 12. Permittivity (ε′) and loss (ε″) determined from capacitance and loss factor. Phase transition temperatures (Tc) are determined. Intra-molecular aromatic interaction and storage capacity are evinced by hysteresis behavior. Data of loss ε″(ω) and permittivity ε′r(ω) recorded in smectic phases infers non-Debye type of asymmetric dispersion. Multiple loss peaks in ε″(ω) is argued to involve distinct time scaled relaxations. Relaxation analyzed by Cole-Davidson method. Re-orientation of longitudinal dipole moment μ to the field analyzed. μ is resolved by rigid core, intra-molecular repulsive and flexible end-chain components. Observed distinct time scale response confirms dipolar components. Trends of relaxation frequency, activation energy, loss maxima, dielectric strength and distribution parameter are analyzed in device perspective. Relaxation and order director fluctuations (ODF) analyzed. ODF suggest the device utility in high temperature smectic phases far away from critical fluctuations.

Double Fano resonance in gold nanotube embedded with a concentric elliptical cylinder

Optical properties of the concentric composite nanostructure composed of gold nanotube around the center gold elliptical core are investigated based on the finite difference time domain method. According to the simulated absorption and scattering spectra, electric field distributions and charge distributions, we can generate double dipole-dipole Fano resonances by adjusting the angle between the elliptical cylinder core and the linearly polarized excitation light, which is due mainly to the interference between the subradiant dipole mode and the superradiant dipole mode. The narrow, low-energy subradiant mode originates from the symmetric hybrization between the longitudinal or transverse dipole mode of the elliptical cylinder core and the dipole bonding mode of the nanotube, and the broad, high-energy superradiant mode originates from the symmetric hybrization between the core’s dipole mode and the nanotube’s dipole antibonding mode. Moreover, the intensities and spectral positions of the two Fano resonances can be manipulated by modifying the geometric parameters of the composite structure. By increasing the semiminor axis of elliptical core, the high-energy Fano resonance red-shifts faster than the low-energy Fano resonance due to the increase of the interaction coupling between the transverse dipole mode of the core and the dipole mode of the nanotube, and becomes weaker in the scattering spectrum because of the reduced radiation intensity of the superradiant dipole mode. When the semimajor axis is changed, a similar phenomenon occurs in the low-energy Fano resonance. In addition, the two Fano resonances red-shift when outer radius of the nanotube increases, but the shift of low-frequency and high-frequency Fano resonance are inconsistent as the inner radius of the nanotube changes. The high-frequency Fano resonance red-shifts monotonically while the low-frequency Fano resonance first blue-shifts and then red-shifts with the increase of inner radius of nanotube because the red shift of the dipole bonding nanotube mode competes with the spectral shifts induced by the diminishing hybridization between elliptical core and nanotube mode. It can also be concluded that the dipole-dipole Fano resonances become apparent and higher order Fano resonance occurs when the composite nanostructure is scaled to a larger size due to the increased radiative damping. With the core and nanotube size fixed, Fano resonance is insensitive to the change of the external environment, but has a good response to the nuclear material of the nanotube.

Dynamic Modulation of Plasmonic Structures

A method for active switching of plasmonic structures by surface oxide-stabilized silver deposition is presented. The longitudinal dipole mode in pairsof closely spaced gold nanodisks on ITO was switched by depositing andremoving a connecting layer of silver in solution. Optical properties werestudied using VIS-NIR extinction spectroscopy and confirmed by FDTDsimulations. Uniform dimensional growth by selective silver depositionbrought pairs of gold nanodisks of 73 nm average diameter and 11 nmaverage distance into electrical contact. The growth process was studied byspectroelectrochemical measurements, and uniformity and selectivity wereconfirmed by SEM and XPS analysis, respectively. Uniform deposition wasachieved by introduction of surface oxides on immobilized gold nanodisks,and selectivity by undervoltage deposition. Deposition of silver on disk pairscaused a blue-shift of the transverse dipole mode resonance of roughly 50 nm,and emergence of a new longitudinal mode with resonance around 960 nm.These results demonstrate the possibility for not only tuning of resonancepeak position, but also on-demand switching of an additional mode which canprovide materials with switchable optical properties.

Magnetic cross-talk simulation between Q2 and L-bend magnets of APS-U

The Advanced Photon Source Upgrade project (APS-U) will replace the present storage ring of the Advanced Photon Source (APS) with a new storage ring based on a multi-bend achromat (MBA) lattice. Due to the increased number of magnets in each sector of the MBA lattice, the space between magnets is very limited, with the smallest separation between magnets being only 5 cm between the Q2 quadrupole in the doublet section and the adjacent M1 longitudinal gradient dipole (L-bend). Cross-talk between these magnets is of concern and is investigated in this work. Both magnets are modeled separately in Opera-3D, and then together as per their design layout in the MBA lattice. The trajectory of a 6.0 GeV electron beam through both magnets is calculated, the local field multipoles along that trajectory computed, and the integrated harmonics compared with a superposition of the fields in the individual magnets. These simulations show that the integrated quadrupole field of the Q2 magnet drops by 0.16% due to the presence of the M1, while the integrated dipole field of the M1 is practically unaffected. The effect on the higher-order multipoles at a radius of 10 mm was less than 0.01% of the integrated dipole field, and is within acceptable limits. The detailed magnetic structures of the Q2 and the M1, electron beam trajectory through these magnets, the local main and harmonic fields along the trajectory, and their integrals with and without cross-talk are reported.

Toroidal dipole bound states in the continuum

Toroidal multipole moments are usually underestimated as they are quite weak in most cases of light-matter interaction. Herein, we reveal a strong link between the toroidal dipole resonance and the bound state in the continuum in the context of all-dielectric metasurfaces. We introduce the concept of toroidal dipole bound states in the continuum, in which two eigenmodes of the silicon metasurface exhibit an intrinsic toroidal dipolar character and have an infinite lifetime. They can be classified as transverse (trivial) and longitudinal (nontrivial) toroidal dipole modes, which correspond to symmetry unprotected and protected bound states in the continuum, respectively. We demonstrate that such toroidal bound states in the continuum supported by the symmetry metasurface can be turned into ultrahigh-$Q$ resonances with a dominant toroidal dipole excitation, which validates their physical origin associated with the ultrahigh-$Q$ toroidal dipole leaky resonances. A full multipole decomposition with dispersive, lossy, and substrate effects further validates that the proposed concept is general and can also be generalized to other structures.

Effect of Central Longitudinal Dipole Interactions on Chiral Liquid-Crystal Phases

Monte Carlo simulations of chiral liquid-crystals, represented by a simple coarse-grained chiral Gay–Berne model, were performed to investigate the effect of central longitudinal dipole interactions on phase behavior. A systematic analysis of the structural properties and phase behavior of both achiral and chiral systems, with dipole interactions, reveals differing effects; strong dipole interactions enhance the formation of layered structures; however, chiral interactions may prevent the formation of such phases under certain conditions. We also observed a short-ranged smectic structure within the cholesteric phases with strong dipole interactions. This constitutes possible evidence of presmectic ordering and/or the existence of chiral line liquid phases, which have previously been observed in X-ray experiments to occur between the smectic twisted grain boundary and cholesteric phases. These results provide a systematic understanding of how the phase behavior of chiral liquid-crystals changes when alterations are made to the strength of dipole interactions.

Performance comparison of different ultralow emittance unit cells

The available minimum emittance of a storage ring and the ring performance is closely related to the unit cell of the lattice. Up to now, several ultralow-emittance unit cells have been proposed and applied in the lattice design of the diffraction-limited storage ring light sources. In this study we quantitatively compared the performance of three typical unit cells, based on mainly the parameters of the High Energy Photon Source. The results indicate that the modified-TME unit cell with antibend and longitudinal gradient dipole allows the lowest possible emittance, given a long enough cell length.

Tuning of 3-tap bandpass filter during acceleration for longitudinal beam stabilization at FAIR

During acceleration in the heavy-ion synchrotrons SIS18/SIS100 at GSI/FAIR longitudinal beam oscillations are expected to occur. To reduce longitudinal emittance blowup, dedicated LLRF beam feedback systems are planned. To date, damping of longitudinal beam oscillations has been demonstrated in SIS18 machine experiments with a 3-tap filter controller (e.g. [1]), which is robust in regard to control parameters and also to noise. On acceleration ramps the control parameters have to be adjusted to the varying synchrotron frequency. Previous results from beam experiments at GSI indicate that a proportional tuning rule for one parameter and an inversely proportional tuning rule for a second parameter is feasible, but the obtained damping rate may not be optimal for all synchrotron frequencies during the ramp. In this work, macro-particle simulations are performed to evaluate, whether it is sufficient to adjust the control parameters proportionally (inversely proportionally) to the change in the linear synchrotron frequency, or if it is necessary to take more parameters, such as bunch-length and synchronous phase, into account to achieve stability and a considerable high damping rate for excited longitudinal dipole beam oscillations. This is done for single- and dual-harmonic acceleration ramps.

Tuning of 3-tap Bandpass Filter During Acceleration for Longitudinal Beam Stabilization at FAIR

During acceleration in the heavy-ion synchrotrons SIS18/SIS100 at GSI/FAIR longitudinal beam oscillations are expected to occur. To reduce longitudinal emittance blowup, dedicated LLRF beam feedback systems are planned. To date, damping of longitudinal beam oscillations has been demonstrated in SIS18 machine experiments with a 3-tap filter controller (e.g. [1]), which is robust in regard to control parameters and also to noise. On acceleration ramps the control parameters have to be adjusted to the varying synchrotron frequency. Previous results from beam experiments at GSI indicate that a proportional tuning rule for one parameter and an inversely proportional tuning rule for a second parameter is feasible, but the obtained damping rate may not be optimal for all synchrotron frequencies during the ramp. In this work, macro-particle simulations are performed to evaluate, whether it is sufficient to adjust the control parameters proportionally (inversely proportionally) to the change in the linear synchrotron frequency, or if it is necessary to take more parameters, such as bunch-length and synchronous phase, into account to achieve stability and a considerable high damping rate for excited longitudinal dipole beam oscillations. This is done for single- and dual-harmonic acceleration ramps.

Development of Novel Solid-State Light-Emitting Materials Based on Pentafluorinated Tolane Fluorophores.

We herein describe the synthesis of novel pentafluorinated tolane fluorophores, which possess an extended π-conjugated structure with a large molecular dipole moment along the longitudinal axis. We also report a detailed evaluation of both the photophysical and thermal behaviors of these fluorophores. All molecules displayed photoluminescence (PL) characteristics in both the crystalline state and in dilute solutions. The large longitudinal dipole moment induced solvatochromic PL behavior, which switched sensitively with changes in the solvent polarity. In addition, incorporation of the fluorinated tolane-based solid-state light-emitting moiety into the polymer side chain was found to be responsible for the PL characteristics observed in the solid state. It was also noteworthy that the polymerization protocol led to a significant enhancement in the thermal stability, with the thermal decomposition temperature increased by 90 °C. Accordingly, novel solid-state light-emitting materials with high thermal stabilities were successfully developed as promising candidates for use in light-emitting and optoelectronic applications.

Nanofocusing of Toroidal Dipole for Simultaneously Enhanced Electric and Magnetic Fields Using Plasmonic Waveguide

Optical toroidal dipole and electromagnetic field enhancement have attracted much interest owing to their interesting physical features and various potential nanophotonic applications. In this paper, novel antireflective nanofocusing methods to deliver and squeeze toroidal dipole moment with simultaneous enhancement of electric and magnetic fields are suggested. By coupling the two fundamental modes of a metal–insulator–metal waveguide with a partial mirror in a waveguide and a nanocavity, resonant squeezing of longitudinal and perpendicular toroidal dipoles in an ultracompact nanocavity (∼ λ 2 / 190) is achieved at the near-telecom wavelengths. Moreover, electric and magnetic field enhancements occur simultaneously in a designated nanocavity. We expect that the proposed scheme would pave a way to engineer nanophotonic waveguide based light-matter interactions by enhancing both electric and magnetic fields. This study would interest both nanophotonics and quantum optics communities.

Relaxation, de Vries behavior, and layer contraction in chiral liquid crystal by dielectric spectroscopy

ABSTRACTLow-frequency (LF) (20 Hz to 10 MHz) field response investigations are reported in TSiKN65F series-based chiral liquid crystal compound, C-10, viz., 1-[3ʹ-nitro-4ʹ-S-(2-decyloxy)phenyl]phenyl-4-(1,1,1,3,5,5,5-heptamethyltrisiloxydecyloxy)-3-Fluorobenzoate. Molecular frame with 10-methylene units and a chiral center on one end is connected to the core with 3-phenyl rings. Other end of core connected to biforked trisiloxy chain to promote de Vries phase. Isotropic-smectic-A and smectic-A-smectic-C*deVr transitions are determined by capacitance study. DC field reversal and polarized optical microscopy textures confirmed occurrence of SmC*deVr phase below SmA. Hysteresis is observed in SmC*deVr. Tilt order parameter growth estimated in SmC*deVr phase through β equal to 0.673 agrees with mean field prediction. Relaxation behavior in kilo Hertz region is explained through longitudinal dipole moment μl reorientation. Dynamics studied through LF dielectric relaxation infers dominance of order director fluctuations at few kilohertz. Higher activation energy in de Vries phase infers greater degrees of freedom and additional constraints. Loss ε″(T) exhibited anomalous trend at SmA-to-SmC*deVr interface. Temperature variation of tilt θ(T) is estimated from loss. Loss in de Vries phase gets suppressed by field to infer collective response. Curie–Weiss behavior by γ-exponent ~0.03 infers weaker ferroelectric response in SmC*deVr phase. Loss variation ε″(T) addressed by perturbed bookshelf model reveals marginal layer contraction by <1% in SmC*deVr phase. Estimates of layer shrinkage through R- and f-parameters in SmC*deVr phase confirm the de Vries behavior.

Large Third-Order Optical Susceptibility with Good Nonlinear Figures of Merit Induced by Octupole Plasmon Resonance of Asymmetric Au–Ag Core–Shell Nanorods

The Au–Ag core–shell nanorods with asymmetric transverse cross section are synthesized, and their tunable linear and nonlinear optical responses are investigated. After the overgrowth of the asymmetric Ag shell on the Au nanorods, (i) a strong transverse octupole (TO) plasmon resonance at 390 nm is observed; (ii) the nonlinear refractive index γ at the TO resonance wavelength significantly increases from −0.15 × 10–4 to −0.85 × 10–4 cm2/GW, and the γ at the longitudinal dipole (LD) resonance wavelength slightly increases from −0.42 × 10–4 to −0.58 × 10–4 cm2/GW; (iii) but the nonlinear absorption coefficient β induced by the TO resonance is approximately 1 order of magnitude smaller than the one induced by the LD resonance. Consequently, the asymmetric Au–Ag core–shell nanorods at the TO resonance wavelength demonstrate a very large nonlinear refractive index as well as excellent nonlinear figures of merit (W = 4.4 > 1 and T = 0.14 < 1), which satisfy the demands for waveguide all-optical switching.

Fano Resonance in a Metasurface Composed of Graphene Ribbon Superlattice

We present a metasurface composed of graphene ribbon superlattice that supports plasmonic Fano resonance in a simple symmetric configuration. Without the necessity of changing the geometry size of graphene ribbons, we tune the Fano resonance of the metasurface containing identical graphene ribbons by simply changing the global or local periods of the superlattice. The increase of the global period of the superlattice leads to a blue-shift of the broad resonance of the bright mode, while the increase of the local period leads to simultaneous shifts of the broad resonance of the bright mode and the sharp resonance of the dark mode toward opposite direction with respect to each other. The resonance shift mechanism can be well explained by the restoring force model for longitudinal dipole arrays. In addition, the overall spectral position of the Fano resonance can be actively tuned by the fermi level of graphene ribbons. Our methods provide a simple and flexible pathway to tune the plasmonic Fano resonance, which holds great potentials for tunable biosensing and slow light applications with improved performance.

Enhancement of Raman scattering from single-walled carbon nanotubes on densely-arranged two-dimensional gold nanoparticle assemblies

ABSTRACTWe investigated surface-enhanced Raman scattering properties of single-stranded DNA-functionalized single-walled carbon nanotubes (ssDNA-SWCNTs) modified on densely-arranged two-dimensional Au nanoparticle assemblies. The ssDNA-SWCNTs was prepared by sonicating a mixture solution of the ssDNA and high-pressure carbon monoxide (Hipco) SWNTs. The Au nanoparticle assemblies were prepared by an organic solvent-mediated liquid-liquid interface assembly technique. The assemblies showed a strong longitudinal dipole coupling mode, which lead to the generation of hot spots at a near infrared region. The Raman signals characteristic of the SWCNTs were significantly enhanced (average enhancement factor: 199) by the coupling mode.

High figure of merit hydrogen sensor using multipolar plasmon resonance modes

Fabrication of long Au nanorods (AuNRs) has resulted in the appearance of higher order plasmon resonance modes, or multipoles, in the absorbance spectrum that can be monitored as a function of time and gas exposure. Due to the proximity of the multipolar mode to the transverse dipole mode of the AuNRs, both modes were monitored as the sample was exposed to hydrogen in an air background. These results were also compared to a shorter AuNR sample where the longitudinal dipole peak position matched the multipolar peak position. Polarization dependence of the higher order resonance as well as boundary element method (BEM) simulations confirm that the mode order is n=3. Due to the 36% decrease in linewidth of the multipolar peak compared to the dipole, the figure of merit (FoM) of the multipolar resonance is calculated to be 22% higher than the longitudinal dipole resonance for the shown gas sensing results and is promising for high temperature gas sensing applications.

A fracture evaluation by acoustic logging technology in oil-based mud: A case from tight sandstone reservoirs in Keshen area of Kuqa Depression, Tarim Basin, NW China

Abstract To solve the problem of poor fracture identifying effect on electrical logging in oil-based mud, the application of acoustic logging to the quantitative characterisation of fractures is expanded from three aspects, namely, Stoneley waves, longitudinal and transverse waves and cross dipole acoustic waves, and a fracture logging evaluation model closely related to production capacity is established considering the radial extension characteristics of fractures. The Stoneley reflection coefficient is used to determine fractures locations to help detect fractures during normal micro-resistivity imaging logging. Based on the experiment on the relationship between fracture width and acoustic attenuation coefficient, empirical formulae for calculating fracture width have been established by primary wave and shear wave energy information considering the effect of porosity. The new parameters, including spectrum correlation coefficient and energy difference from cross dipole array acoustic logging data, can be used for fractures evaluation. The more developed the fractures are, the greater the energy difference becomes, and the smaller the spectrum correlation coefficient is, the higher the production is. The fracture effective evaluation parameters can be separated into two components, specified as the degree of fracture vertical opening and radial extension. Combining the conventional logging and array acoustic logging (including cross dipole array acoustic logging), a fracture radial extension evaluation model is presented closely related to productivity.

1,2,3]-triazole derivatives: Mesomorphic property dependence on the molecular shape

ABSTRACTNowadays, heterocyclic units have been extensively studied for the preparation of thermotropic liquid crystals due to their ability to impart lateral and/or longitudinal dipoles and induce changes in molecular shape. Key parameters to accede to stable mesophases are the position of the heterocycle and the nature of terminal and linking functions. We present in this paper, an overview of several series of 1,2,3-triazole liquid crystalline derivatives that we designed and characterized. We highlight the effect of different connecting functions and the geometry of mesogenic core on the mesomorphic behavior of these derivatives.

The substantial model of the photon

It is shown that the angular frequency of the photon is nothing else than the averaged angular frequency of revolution of the electron cloud’s center during emission and quantum transition between two energy levels in an atom. On assumption that the photon consists of charged particles of the vacuum field (of praons), the substantial model of a photon is constructed. Praons move inside the photon in the same way as they must move in the electromagnetic field of the emitting electron, while internal periodic wave structure is formed inside the photon. The properties of praons, including their mass, charge and speed, are derived in the framework of the theory of infinite nesting of matter. At the same time, praons are part of nucleons and leptons just as nucleons are the basis of neutron stars and the matter of ordinary stars and planets. With the help of the Lorentz transformations, which correlate the laboratory reference frame and the reference frame, co-moving with the praons inside the photon, transformation of the electromagnetic field components is performed. This allows us to calculate the longitudinal magnetic field and magnetic dipole moment of the photon, and to understand the relation between the transverse components of the electric and magnetic fields, connected by a coefficient in the form of the speed of light. The total rest mass of the particles making up the photon is found, it turns out to be inversely proportional to the nuclear charge number of the hydrogen-like atom, which emits the photon.

Derivation of the magnetic field on a metal cylinder excited by a longitudinal magnetic dipole transmitter: II. Cylinder in a two‐layer dissipative dielectric medium

AbstractWe derive an exact convergent analytical solution for the complex frequency‐dependent magnetic field on the surface of an infinitely long and perfectly conducting metal cylinder situated in a cylindrically layered dissipative medium. The inhomogeneous medium consists of two exterior cylindrical layers that are concentric with the cylinder. The magnetic field on the cylinder is excited by a longitudinally oriented oscillating magnetic dipole transmitter on the cylinder surface. An exact analytical solution to this problem has not been previously published and is of theoretical as well as practical importance, e.g., in modeling the responses of electromagnetic wave propagation well logging tools. It is shown that the magnetic field on the cylinder surface can be expressed as a real‐axis integral; however, the integrand oscillates rapidly and diverges for large values of the integration variable. The real‐axis integral is replaced by the sum of two convergent branch line integrals and a sum over the residues of the complex poles in the integrand of the real‐axis integral. The poles correspond physically to waveguide modes that propagate with discrete wave numbers. A pole search algorithm is developed to locate the positions of the poles and compute their residues. Phase shifts and attenuations of the magnetic field between receivers for a 1.1 GHz well logging tool are computed to elucidate the pole spectra and the relative contributions of the waveguide modes and the branch cut integrals for different thicknesses of the innermost dielectric layer and for different layer properties.