Anomalous Dispersion Curves Research Articles

Evidence of metamaterial physics at the geophysics scale: the METAFORET experiment

Abstract The METAFORET experiment was designed to demonstrate that complex wave physics phenomena classically observed at the meso- and micro-scales in acoustics and in optics also apply at the geophysics scale. In particular, the experiment shows that a dense forest of trees can behave as a locally resonant metamaterial for seismic surface waves. The dense arrangement of trees anchored into the ground creates anomalous dispersion curves for surface waves, which highlight a large frequency band-gap around one resonant frequency of the trees, at ∼45 Hz. This demonstration is carried out through the deployment of a dense seismic array of ∼1000 autonomous geophones providing seismic recordings under vibrating source excitation at the transition between an open field and a forest. Additional geophysical equipment was deployed (e.g. ground-penetrating radar, velocimeters on trees) to provide essential complementary measurements. Insights and interpretations on the observed seismic wavefield, including the attenuation length, the intensity ratio between the field and the forest and the surface wave polarization, are validated with 2D numerical simulations of trees over a layered halfspace.

Complex Refractive Index Dispersion of Strong Absorbing Material Determined Using Internal Reflectance Spectra Measurement.

Complex refractive index dispersion (CRID) of offset inks is an important spectral property that affects the quality of printing. Due to the strong absorption of offset inks, great difficulty exists when measuring their CRID. In this study, a recently proposed apparatus that can detect the internal reflectance spectra was used to measure the CRID of three strong absorbing offset inks (magenta, yellow, and cyan). Both anomalous dispersion curve and extinction coefficient curve were well determined over the spectral range of 400-750 nm. This study experimentally proves that the apparatus and related method are feasible for the CRID measurement of strong absorbing materials and could serve as a powerful measuring tool for optical parameters.

Asymmetrical bonding in liquid Bi disentangled by inelastic X-ray scattering

The structure of liquid Bi has been debated in relationship with the Peierls distortion, as crystalline Bi takes A7 structure. A recent ab initio molec- ular dynamics simulation for liquid Bi predicted a flat-topped profile of the acoustic dispersion curve. To confirm the prediction, we have carried out inelas- tic x-ray scattering (IXS) for liquid Bi. The dynamic structure factor obtained by the IXS exhibits a distinct inelastic excitation of the longitudinal acoustic mode up to 14 nm −1 and the dispersion curve of the excitation energy obtained by the memory function analysis becomes a flat-topped one. We found that a linear chain model including the interatomic interaction with the second near- est neighbors can explain the flat-topped profile. The result suggests that the anomalous dispersion curve in liquid Bi arises from local anisotropy related to the Peierls distortion in the crystalline phase. .

Surface polaritons in planar chiral nihility meta-material waveguides

Chiral nihility meta-material is a special case of chiral medium, in which both the permittivity and permeability are equal to zero. The feature of surface wave modes (or surface polaritons) in the planar chiral nihility waveguides which the core or cladding consist of chiral nihility meta-materials is investigated. The dispersion curves, electromagnetic fields, energy flow distribution and the power of surface wave modes in the planar chiral nihility waveguides are presented for typical parameters. Some novel peculiarities such as anomalous dispersion curves, the power flows opposite to the wave vector propagation direction in the planar chiral nihility waveguides have been found.

CHARACTERISTICS OF GUIDED MODES IN PLANAR CHIRAL NIHILITY META-MATERIAL WAVEGUIDES

The characteristics of guided modes in the planar waveguides which the core or cladding consists of chiral nihility meta-materials are studied theoretically. The dispersion curves, electromagnetic fields, energy flow distribution and the power of several low-order guided modes in the chiral nihility waveguides are presented. Some novel features such as anomalous dispersion curves, the power flows opposite to the wave vector propagation direction in the chiral nihility waveguides have been found.

Zero-group-velocity modes in longitudinally uniform waveguides

We present a longitudinally uniform slow light waveguide, which consists of transverse periodic dielectric strips with a few defect layers. The parameters of the proposed waveguide can be tuned to have two anomalous dispersion curves with extreme points which have zero-group-velocity frequencies at nonzero wave vector in uniform-index direction. The group velocity and group velocity dispersion of the two photonic bands are analyzed, and the propagation of the slow mode with a given bandwidth is demonstrated theoretically.

Anomalous magnetic excitation on triangular lattice antiferromagnet CuFeO2

Abstract The magnetic excitation spectrum has been investigated by inelastic neutron scattering on triangular lattice antiferromagnets CuFeO 2 and CuFe 0.98 Al 0.02 O 2 . While the normal acoustic spin-wave dispersion curve was obtained in CuFe 0.98 Al 0.02 O 2 , the anomalous dispersion curve with energy gap whose bottom positions do not correspond to the magnetic Bragg point for the 4-sublattice (↑↑↓↓) ground state was obtained in CuFeO 2 .

Anomalous surface lattice dynamics of a simple hexagonal close-packed surface

The surface lattice dynamics of Ru(001) has been investigated by a combined first-principles calculation and high-resolution electron-energy-loss spectroscopy. We find very anomalous dispersion curves of low-frequency surface modes and indications of strong softening of longitudinally polarized vibrations. They originate from large modifications of in-plane surface force constants unexpected for such a compact hexagonal surface.

Optical characterisation of 6t and 4t single crystals by ellipsometry; anisotropy and crystalline structure

Ellipsometry and absorption spectroscopies have been carried out on sexithiophene (α-6T), and quaterthiophene (α-4T) single crystals grown at High Temperature (HT) or Low Temperature (LT). Effective Optical Indices (EOI) neff and keff have been obtained in two positions of the crystals: b axis being either perpendicular to the yz incidence plane (α=0 °) or parallel to Oy (α=90 °).The spectra contain only a strong absorption feature around 3.4eV and 3.7eV for 6T and 4T respectively. We have compared experimental data and those obtained by simulation of EOI considering a biaxial semi-infinite medium with its three orthogonal principal axis parallel to Ox, Oy, Oz directions. The strong anisotropy of the 4T and 6T LT forms induces an anomalous dispersion curve of neff and a blue shift of keff (~0.1–0.3eV) regardless of the crystal set. The weak anisotropy of the HT form, leads to an anomalous dispersion and a blue shift for keff (~0.1–0.3eV) only for the crystal set α=0 °. The absorption anisotropy or (kz-kx,y) is related to the angle between the L molecular axis and the crystal plane (b, c).

Ultrasonic properties of one-dimensional (TaSe 4) 2I

We report measurements on the quasi-one-dimensional (TaSe) 2I which undergoes a Peierls transition at T p= 262 K. Softening of the shear elastic constant C 44 has been observed below 40 K. The effective Grüneisen parameter deduced from the sound velocity increases up to 20 when temperature decreases down to 4 K. Such a large increase of Γ eff has been related to the anomalous dispersion curve of the C 44 acoustic branch of this system.

Dependence of valence-subband dispersion relations on heterointerface boundary conditions in InxGa1−xAsyP1−y/InP narrow quantum wells

In the framework of envelope function approximation, the dependence on heterointerface boundary conditions of valence-band dispersion relations in InP-based quantum-well structures is investigated. Under conventional boundary conditions, the root-finding calculation for the eigenvalue problem of quantum well structures is carried out while taking into account a large difference in the effective-mass parameters (the Luttinger parameters) among the constituting bulk materials. In spite of a decreasing interband mixing between heavy- and light-hole states due to strain and the quantum size effect, hole subband structure of a compressive-strained quantum well with a narrow well width is found to form an anomalous dispersion curve. It is clarified that the requirement for envelope continuity at interfaces is responsible for anomaly in the dispersion curves through off-diagonal terms with an additional δ-function-like interface potential in the valence-band effective-mass Hamiltonian. We present the results of dispersion relations and envelope functions related to a newly derived connection rule based on the tight-binding bond-orbital description, under which the envelopes are free from continuity restrictions at the interfaces regardless of any difference in the effective-mass parameters.

Gain anisotropy and simultaneous bidirectional emission of a Doppler-broadened MIR optically-pumped ammonia ring laser

The authors studied the Doppler-broadened 11.76- mu m /sup 15/NH/sub 3/ emission line optically pumped in a ring resonator by a CW CO/sub 2/ laser operating on the 10R(42) line. Behavior related to the optical pumping of gas Doppler-broadened lines is found and shown to be very dependent on the laser parameters. For instance, the laser emission can occur in one direction or two directions simultaneously. A local gain model based on the interaction of two laser fields with a three-level molecular system is used to clarify the emission characteristics of this laser. Basically, the two-photon or Raman process and the Rabi splitting generate a gain anisotropy and an anomalous dispersion curve. The effects lead to a different optical path for the two directions of propagation and, consequently, a simultaneous bidirectional emission with unequal emission frequency.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Anomalous dispersion: a new measurement approach

A technique for instantaneously viewing discrete points along an anomalous dispersion curve has been successfully demonstrated. A Fabry-Perot interferometer was used to spatially resolve the axial modes of an HF probe laser. A Michelson interferometer, one leg of which contained an HF absorption cell, imposed lines of constant phase. Recorded fringe shifts could then be used to determine the refractive-index change between axial mode frequencies, thus enabling construction of the dispersion profile.

The Influence of the Christiansen Effect on I.R. Spectra of Powders

AbstractThe Christiansen effect appears in the i.r. spectrum of powders embedded in a solid, liquid or air matrix as an apparently anomalous transmittance (Christiansen peak) of the incident electromagnetic radiations. The peak appears at wavelengths for which the refractive index of the sample and the refractive index of the matrix are equal (Christiansen wavelength: λChr).On account of the great variation of the sample refractive index in the immediate neighborhood of the absorption bands (anomalous dispersion curve), one often observes the occurrence of a transmittance peak or of a band deformation in this spectral range. A change in the position of this transmission peak with the value of the matrix refractive index is indicative of the Christiansen effect.The equality of the refractive indices of the sample and of the matrix for μChr has been used to determine some points of the anomalous dispersion curve in the neighborhood of the hydroxyl stretching band (3678 cm−1).Spectral distortions caused by the Christiansen effect can be reduced by preparing the sample in such a manner that the width at half-maximum (Δν1/2) of the Christiansen peak is several times greater than this of the absorption band itself. Clarke’s theoretical formula, which gives an estimation of Δν1/2, has been qualitatively verified and thus gives an appropriate guide in the choice of the parameters which one can optimize during the sample preparation. One can reduce the Christiansen effect spectral modifications, without running the risk of modifying the sample itself, particularly by overly severe grinding.

Verification of the Kramers–Kronig relations in optically pumped ruby

The real and imaginary parts of the complex index of refraction have been measured in the R1 line of optically pumped ruby. The experiments, which employed a temperature-controlled, single-mode ruby laser as a variable-frequency monochromatic source, were performed near liquid-nitrogen temperature, where the R1 doublet structure is well resolved. R1 absorption profiles were measured for several optical-pumping conditions, ranging from zero up to a pump power that excited a population in the 2E state equal to about 60% of the population of the 4A2 ground state. For each pumping condition, the anomalous-dispersion curve was measured interferometrically. The spectral profiles of the absorption coefficient and the anomalous dispersion display a dependence on the optical-pumping conditions that is more complicated than simple saturation of the R1 transitions, but for given pumping conditions the two quantities are correlated as predicted by the Kramers–Kronig relations.

Narrow Band Filters Based on Magnetooptical Effects

The theory is developed for two types of narrow band filters. One is based on the Zeeman splitting of the line absorption coefficient; the other is based on the splitting of the anomalous dispersion curves in a Zeeman multiplet. The latter type filter is very similar to the Lyot-Ohman filter. It uses however the Macaluso Corbino effect instead of the linear birefringence of crystals. It is capable of giving very much narrower transmission profiles than the Lyot-Ohman filter and it has a very wide field.

Optical rotatory dispersion and circular dichroism of D-amino acid oxidase.

Abstract The optical rotatory dispersion and circular dichroism of d -amino acid oxidase ( d -amino acid: O 2 oxidoreductase, EC 1.4.3.3, pig kidney) were measured. In the visible region, the holoenzyme showed anomalous dispersion curves with characteristic patterns depending on the state of the coenzyme (FAD or FADH 2 ). The presence of optically active absorption bands was confirmed by measurement of circular dichroism. The anomaly in the disperison curves can be explained by assuming that weak Cotton effects, due to chromophores of the bound coenzyme, are superimposed on the intrinsic dispersion curves of the protein moiety of the enzyme. A plain dispersion curve was observed with the apoenzyme, and it differed significantly from the dispersion curve presumed for the protein moiety of the holoenzyme. In the far-ultraviolet region, the apoenzyme and holoenzyme exhibited identical optical rotatory dispersion and circular dichroism. It is concluded that the two forms of holoenzyme have almost the same conformation, and removal of the coenzyme produces a reversible conformational change in the non-α-helical portion of the protein moiety of the enzyme.

OPTICAL ROTATORY DISPERSION STUDIES. XXXI.1 ANOMALOUS DISPERSION CURVES OF DITHIOCARBAMATES OF α-AMINO ACIDS AND PEPTIDES. STEREOCHEMICAL CORRELATIONS BETWEEN α-HYDROXY AND α-AMINO ACIDS2

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTOPTICAL ROTATORY DISPERSION STUDIES. XXXI.1 ANOMALOUS DISPERSION CURVES OF DITHIOCARBAMATES OF α-AMINO ACIDS AND PEPTIDES. STEREOCHEMICAL CORRELATIONS BETWEEN α-HYDROXY AND α-AMINO ACIDS2Berndt Sjöberg, Arne Fredga, and Carl DjerassiCite this: J. Am. Chem. Soc. 1959, 81, 18, 5002–5003Publication Date (Print):September 1, 1959Publication History Published online1 May 2002Published inissue 1 September 1959https://doi.org/10.1021/ja01527a065RIGHTS & PERMISSIONSArticle Views60Altmetric-Citations31LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (218 KB) Get e-Alerts Get e-Alerts

Wave-Guide Systems with Negative Phase Velocities

IN all smooth wave-guides and many loaded wave-guides the phase velocity has the same sign as the energy velocity. Some systems having complex forms of loading have in the past been attributed with zero or even negative group-velocities, based on apparently anomalous dispersion curves. Such phenomena have been clouded by doubts about the conception of group velocity and its relationship to energy velocity. It has recently been shown that in a periodic structure with negligible attenuation, energy and group velocities are identical1. If a system is analysed in terms of the positive solution for phase velocity, a zerogroup-velocity indicates a form of resonance with zero net power flow, and a negative group-velocity indicates a negative net energy velocity. Since in any experiment the net energy velocity is taken to be positive, systems can be devised in which the phase-velocity is negative. Dispersion curves showing guide and air wave-lengths as ordinates and abscissae must have a positive slope, and in these anomalous systems this requires a negative sign to be attributed to the measured guide wave-lengths. When interaction with charged particles is required, it is of supreme importance to determine the correct direction of the phase-velocity.