Narrow Dip Research Articles

Anelastic spectroscopy study of the metal-insulator transition of Nd1−xEuxNiO3

Measurements are presented of the complex dynamic Young's modulus of NdNiO3 and Nd0.65Eu0.35NiO3 through the Metal-Insulator Transition (MIT). On cooling, the modulus presents a narrow dip at the MIT followed by an abrupt stiffening of ~6%. The anomaly is reproducible between cooling and heating in Nd0:65Eu0:35NiO3 but only appears as a slow stiffening during cooling in undoped NdNiO3, conformingly with the fact that the MIT in RNiO3 changes from strongly first order to second order when the mean R size is decreased. The elastic anomaly seems not to be associated with the antiferromagnetic transition, which is distinct from the MIT in Nd0.65Eu0.35NiO3. It is concluded that the steplike stiffening is due to the disappearance or freezing of dynamic Jahn- Teller (JT) distortions through the MIT, where the JT active Ni3+ is disproportionated into alternating Ni3+d and Ni3-d. The fluctuating octahedral JT distortion necessary to justify the observed jump in the elastic modulus is estimated as ~3%, but does not have a role in determining the MIT, since the otherwise expected precursor softening is not observed.

Outburst of LS V+44 17 observed by MAXI and RXTE discovery of dip structure in pulse profile

We report the discovery of a dip structure in the pulse profile of Be/X-ray binary LS V +44 17 observed by RXTE during an outburst detected by MAXI. The outburst was first transient activity of LS V +44 17 since 1997 when the source was identified as a Be/X-ray binary. After the discovery with MAXI, the RXTE observations provided a pulse profile with a narrow dip structure in the soft X-ray band (3–10 keV). Our pulse-phase-resolved spectroscopy showed that the absorption column density at the dip phase is much higher than those at the other intervals. Thus we can conclude that the partial eclipse of the emission region by the accretion column of the neutron star causes the dip structure in the pulse profile of LS V +44 17 during the first outburst.

Saturn’s F ring grains: Aggregates made of crystalline water ice

We present models of the near-infrared (1–5 μm) spectra of Saturn’s F ring obtained by Cassini’s Visual and Infrared Mapping Spectrometer (VIMS) at ultra-high phase angles (177.4–178.5°). Modeling this spectrum constrains the size distribution, composition, and structure of F ring particles in the 0.1–100 μm size range. These spectra are very different from those obtained at lower phase angles; they lack the familiar 1.5 and 2 μm absorption bands, and the expected 3 μm water ice primary absorption appears as an unusually narrow dip at 2.87 μm. We have modeled these data using multiple approaches. First, we use a simple Mie scattering model to constrain the size distribution and composition of the particles. The Mie model allows us to understand the overall shapes of the spectra in terms of dominance by diffraction at these ultra-high phase angles, and also to demonstrate that the 2.87 μm dip is associated with the Christiansen frequency of water ice (where the real refractive index passes unity). Second, we use a combination of Mie scattering with Effective Medium Theory to probe the effect of porous (but structureless) particles on the overall shape of the spectrum and depth of the 2.87 μm band. Such simple models are not able to capture the shape of this absorption feature well. Finally, we model each particle as an aggregate of discrete monomers, using the Discrete Dipole Approximation (DDA) model, and find a better fit for the depth of the 2.87 μm feature. The DDA models imply a slightly different overall size distribution. We present a simple heuristic model which explains the differences between the Mie and DDA model results. We conclude that the F ring contains aggregate particles with a size distribution that is distinctly narrower than a typical power law, and that the particles are predominantly crystalline water ice.

Coherent scattering by a spherical medium of resonant atoms

We consider the problem of coherent resonant scattering of electromagnetic waves by a spherical medium of two-level atoms. The frequency dependence of the scattering amplitudes and cross sections reveals a complex structure of narrow peaks and dips. We relate these scattering resonances to the cooperative emission resonances characteristic of a sphere. We find the scattering to show considerable interference between the electric and magnetic multipole contributions, particularly in the lower multipole orders. This interference tends to enhance anisotropies in the differential scattering cross section even for small spheres. For such spheres, the peak values of the resonant contributions of the low-order multipoles to the total scattering cross section can increase with multipole order, in contrast to the usual decrease seen in nonresonant scattering.

YSOVAR: THE FIRST SENSITIVE, WIDE-AREA, MID-INFRARED PHOTOMETRIC MONITORING OF THE ORION NEBULA CLUSTER

We present initial results from time series imaging at infrared wavelengths of 0.9 sq. degrees in the Orion Nebula Cluster (ONC). During Fall 2009 we obtained 81 epochs of Spitzer 3.6 and 4.5 micron data over 40 consecutive days. We extracted light curves with ~3% photometric accuracy for ~2000 ONC members ranging from several solar masses down to well below the hydrogen burning mass limit. For many of the stars, we also have time-series photometry obtained at optical (Ic) and/or near-infrared (JKs) wavelengths. Our data set can be mined to determine stellar rotation periods, identify new pre-main-sequence (PMS) eclipsing binaries, search for new substellar Orion members, and help better determine the frequency of circumstellar disks as a function of stellar mass in the ONC. Our primary focus is the unique ability of 3.6 & 4.5 micron variability information to improve our understanding of inner disk processes and structure in the Class I and II young stellar objects (YSOs). In this paper, we provide a brief overview of the YSOVAR Orion data obtained in Fall 2009, and we highlight our light curves for AA-Tau analogs - YSOs with narrow dips in flux, most probably due to disk density structures passing through our line of sight. Detailed follow-up observations are needed in order to better quantify the nature of the obscuring bodies and what this implies for the structure of the inner disks of YSOs.

Non‐linear conductivity of NbS3 in pressure induced metal state

AbstractTemperature and voltage dependencies of conduction of a quasi‐one‐dimensional conductor NbS3 after its transition into a metallic state has been studied at pressures higher than 6 GPa. The differential resistance R = dV /dI measured at small biases (the electric field E below 2 V/cm) demonstrate a considerable growth upon cooling below 20 K accompanied by appearance of the non‐linear conduction.Both the growth and nonlinear conduction disappear at E > 3 V/cm or when the temperature exceeds 40 K. A narrow dip visible only at much smaller fields E < 20 mV/cm is superimposed over that nonlinear background when cooling below 3.7 K. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Transmission and reflection spectra of a photonic crystal with a Raman defects

Features of Raman gain of probe radiation in three-level atoms placed in a defect of a one-dimensional photonic crystal in the presence of laser radiation (pump) at an adjacent high-frequency transition have been theoretically investigated. It has been shown that there is a pump intensity range where narrow peaks (resonances) simultaneously appear in the transmission and reflection spectra of the probe field. Beyond this region, the peak in the transmission spectrum is transformed to a narrow dip. The spectral position of these peaks is determined by the Raman resonance and the transmittance and reflectance can be larger than unity at pump intensities from several microwatts per square centimeter to several tens of milliwatts per square centimeter. The nature of narrow peaks is due to a sharp dispersion of a nonlinear refractive index near the Raman resonance; this dispersion is responsible for a strong decrease in the group velocity of probe radiation. The proposed scheme makes it possible to obtain controlled ultranarrow resonances in the transmission and reflection spectra of the photonic crystal.

Ultranarrow resonance peaks in the transmission and reflection spectra of a photonic crystal cavity with Raman gain

The Raman gain of a probe light in a three-state $\ensuremath{\Lambda}$ scheme placed into a defect of a one-dimensional photonic crystal is studied theoretically. We show that there exists a pump intensity range, where the transmission and reflection spectra of the probe field exhibit simultaneously occurring narrow peaks (resonances) whose position is determined by the Raman resonance. Transmission and reflection coefficients can be larger than unity at pump intensities on the order of tens of $\ensuremath{\mu}\text{W}/{\text{cm}}^{2}$. When the pump intensity is outside this region, the peak in the transmission spectrum turns into a narrow dip. The nature of narrow resonances is attributed to a drastic dispersion of the nonlinear refractive index in the vicinity of the Raman transition, which leads to a significant reduction in the group velocity of the probe wave.

Theoretical analysis of a fiber optic surface plasmon resonance sensor utilizing a Bragg grating

A rigorous theoretical analysis of a fiber optic surface plasmon resonance sensor is presented. The sensor is based on the spectroscopy of mixed surface plasmon--fiber cladding modes excited by the fundamental mode of an optical fiber via a Bragg grating formed in the fiber core. The transmission spectrum is calculated by means of the Coupled Mode Theory. The modal structure is theoretically analyzed using a 3-D method based on a field expansion approach for matching the field continuity at the boundary of the layers. The theoretical analysis revealed a series of narrow transmission dips associated with the coupling of the fundamental mode to the mixed surface plasmon--fiber cladding modes. The sensitivity of these dips to changes in the refractive index of the analyte is calculated. Moreover, the refractive index resolution of the sensor was estimated to be better than 2 x 10(-6) RIU.

Metal-in-metal localized surface plasmon resonance

Anomalous strong resonances in silver and gold nanoporous thin films which conduct arefound to arise from isolated metal nano-islands separated from the surrounding percolatingmetal network by a thin loop of insulator. This observed resonant optical response ismodelled. The observed peak position is in agreement with the observed averagedimensions of the silver core and insulator shell. As the insulating ring thickness shrinks,the resonance moves to longer wavelengths and strengthens. This structure is the Babinet’sprinciple counterpart of dielectric core–metal shell nanoparticles embedded in dielectric.Like for the latter, tuning of resonant absorption is possible, but here the matrix reflectsrather than transmits, and tuning to longer wavelengths is more practical. A new class ofmetal mirror occurring as a single thin layer is identified using the same resonancesin dense metal mirrors. Narrow band deep localized dips in reflectance result.

Nonlinear conductivity of NbS3 in a high-pressure metallic phase

The temperature dependence of the conductivity of a quasi-one-dimensional NbS3 conductor after its transition to a metallic state has been measured at a pressure higher than 6 GPa. A region of an increased differential resistance rapidly disappearing above 40 K has been observed in low electric fields ≤4 V/cm. A narrow dip against the background of this region appears in the resistance below 3.7 K.

Electrical breakdown at low pressure for planar microelectromechanical systems with <inline-formula><math display="inline" overflow="scroll"><mrow><mn>10</mn><mtext>-</mtext><mspace width="0.3em" /><mtext>to</mtext><mspace width="0.3em" /><mn>500</mn><mtext>-</mtext><mi>μ</mi><mi mathvariant="normal">m</mi></mrow></math></inline-formula> gaps

An experimental study of the dc breakdown voltage for planar MEMS interdigitated aluminum electrodes with gaps ranging from 10 to 500 micron is presented. Unlike most research on the breakdown in MEMS electrodes that was performed at atmospheric pressure, this work focuses on the effect of gas pressure and gas type on breakdown voltage, because this is central for chip-scale plasma generation and for reliable operation in aerospace applications. The breakdown voltage is measured in helium, argon, and nitrogen atmospheres for pressures between 10^2 to 8.10^4 Pa (1 to 800 mbar). For higher values of the pressure P, or of the gap d (i.e., for high values of the Paschen reduced variable P_red=P·d), classical Paschen scaling is observed. For lower values of P_red, however, significant deviations are seen: the Vbd versus. Pd curve shows an extended flat region rather than a narrow dip. These differences cannot be attributed to field emission, but are due to the many length scales effectively present in a planar geometry (on-chip and even off-chip) that leads to the superposition of several Paschen curves. Guidelines are formulated for low-pressure operation of MEMS to avoid or encourage breakdown.

Absorption-free superluminal light propagation in a quantum-dot molecule

The propagation of a weak probe field in a three-level quantum-dot molecule is investigated by employing the tunnel coupling. It is shown that in the absence of tunnel coupling, the propagation of light pulse is superluminal, similar to a simple two-level system. A high-resolution dip appears in optical spectra due to the presence of tunnel coupling. We show that this narrow dip leads to the subluminal light propagation with doublet absorption, so the group velocity of a light pulse can be controlled by interdot tunnel coupling. It is also demonstrated that by applying an indirect incoherent pumping field to the probe transition, the absorption doublet switches to the gain doublet and then the absorption-free superluminal light propagation is appeared.

The evolution of the Lyα forest effective optical depth following He ii reionization

Three independent observational studies have now detected a narrow (\Delta z ~ 0.5) dip centred at z=3.2 in the otherwise smooth redshift evolution of the Lya forest effective optical depth. This feature has previously been interpreted as an indirect signature of rapid photo-heating in the IGM during the epoch of HeII reionisation. We examine this interpretation using a semi-analytic model of inhomogeneous HeII reionisation and high resolution hydrodynamical simulations of the Lya forest. We instead find that a rapid (\Delta z ~ 0.2) boost to the IGM temperature (\Delta T ~ 10^4 K) beginning at z=3.4 produces a well understood and generic evolution in the Lya effective optical depth, where a sudden reduction in the opacity is followed by a gradual, monotonic recovery driven largely by adiabatic cooling in the low density IGM. This behaviour is inconsistent with the narrow feature in the observational data. If photo-heating during HeII reionisation is instead extended over several redshift units, as recent theoretical studies suggest, then the Lya opacity will evolve smoothly with redshift. We conclude that the sharp dip observed in the Lya forest effective optical depth is instead most likely due to a narrow peak in the hydrogen photo-ionisation rate around z=3.2, and suggest that it may arise from the modulation of either reprocessed radiation during HeII reionisation, or the opacity of Lyman limit systems.

Profile Analysis of Arizona Specific Pavement Studies 5 Project

This paper characterizes the longitudinal profiles of 11 pavement sections within the Arizona Long-Term Pavement Performance Specific Pavement Studies 5 project throughout their service life. The flexible pavements associated with this project were rehabilitated and monitored as part of the study. Road profile measurements were collected on the in-service pavement before rehabilitation and 12 times over the 16 years afterward. Detailed profile analyses of the sections, including calculating roughness values, examining the spatial distribution of roughness, viewing with postprocessing filters, and examining spectral properties are included here. The value of examining performance with the full suite of methods is demonstrated, and these analyses provided a basis for quantifying and explaining the changes in localized roughness and overall roughness with time as well as for linking profile properties to each section's maintenance history and observations of surface distress. The analysis showed that the two test sections with a 2-in. recycled overlay exhibited the largest postrehabilitation increase in roughness. The two test sections with a 5-in. virgin overlay exhibited the smallest postrehabilitation increase in roughness. Much of the increase in roughness on the roughest test sections was caused by narrow dips at transverse cracks.

Structural color via layer-by-layer deposition: layered nanoparticle arrays with near-UV and visible reflectivity bands

The same near-ultraviolet (NUV) (300–400 nm) light that facilitates photo-degradation in polymers is also a key component in animal communication, particularly in insects and birds. We developed a nature-inspired 1D photonic crystal structure that has simultaneous narrow stop bands in the NUV and visible wavelength range, resulting in a NUV reflector with tunable structural color in the visible region of the spectrum. The samples were prepared by high precision deposition of alternating stacks of SiO2 and more densely packed TiO2nanoparticlesvia aqueous layer-by-layer (LbL) deposition. Multilayer thin films with eleven stacks achieved up to 75% reflectance with a 50 nm bandwidth and 65% reflectance with a 100 nm bandwidth for structural colors centered at 500 nm and 690 nm, respectively. Despite UV absorbance of the TiO2nanoparticles and the supporting glass substrate, all samples exhibited a narrow NUV stop-band centered in the 300–400 nm range with a reflectance over 65%. Upon introduction of a defect mode, we also demonstrated the creation of a narrow reflectance dip associated with a localized state in the photonic band gap. Multilayer-based structural colors with NUV reflectivity can be used as pigments that can promote prevention of photo-degradation in coatings, in addition to bird and insect repelling functionality.

Modification of the absorption spectrum by stochastic-noise-induced quantum interference

The absorption spectrum is considered for a two-level atom coherently driven by a laser field and incoherently perturbed by stochastic noise. In the noise-dominated regime where incoherent perturbation far exceeds coherent excitation, the amplifying and dispersionlike components in the standard absorption spectrum [B. R. Mollow, Phys. Rev. A 5, 2217 (1972); F. Y. Wu et al., Phys. Rev. Lett 38, 1077 (1977)] develop into an absorption peak and a narrow dip, respectively. The modified absorption spectrum is attributed to the quantum interference induced by stochastic noise.

Absorptive reduction and width narrowing in λ-type atoms confined between two dielectric walls

This paper investigates the absorptive reduction and the width narrowing of electromagnetically induced transparency (EIT) in a thin vapour film of λ-type atoms confined between two dielectric walls whose thickness is comparable with the wavelength of the probe field. The absorptive lines of the weak probe field exhibit strong reductions and very narrow EIT dips, which mainly results from the velocity slow-down effects and transient behaviour of atoms in a confined system. It is also shown that the lines are modified by the strength of the coupling field and the ratio of L/λ, with L the film thickness and λ the wavelength of the probe field. A simple robust recipe for EIT in a thin medium is achievable in experiment.

Plasmonic Notch Filter Design Based on Long-range Surface Plasmon Excitation Along Metal Grating

A single notch plasmonic spectral filter design using evanescently coupled resonant ultrathin metal grating is numerically studied in this article. Due to excitation and coupling of long range surface plasmon between the metal grating nanowires, a deep and narrow reflection spectrum dip can be obtained. Narrower spectral bandwidth is achieved through decreased damping from the existence of large dielectric gaps between the grating nanowires. This physical explanation is confirmed by the field distribution calculation. As an example, a single notch filter design with full width half maximum band width less than 3 nm centered at 808 nm is presented.

Simulation of surface plasmon resonance of Au–WO3−x and Ag–WO3−x nanocomposite films

Abstract Surface plasmon resonance (SPR) has been efficiently employed for chemical- and bio-sensing in numerous fields such as molecular biology, medicine, biotechnology, drug and food monitoring, and environmental monitoring. Nanocomposite thin films formed by noble metal nanoparticles embedded in a dielectric matrix show attractive SPR phenomenon due to collective excitations of conduction electrons in metal nanoparticles when photons are coupled to the metal particle–dielectric interface. In this paper, the SPR responses of Au–WO3−x and Ag–WO3−x nanocomposite films with either stoichiometric (x = 0) and non-stoichiometric (x > 0) structures were simulated using effective medium theory and Macleod's general characteristic matrices method for various metal percentages and film thicknesses in the Kretschmann configuration at the wavelength of 632.8 nm. Our simulation results predicted that the most suitable Au percentage and film thickness when using non-stoichiometric Au–WO3−x films for SPR gas sensing were 60–80 vol.% of Au with 30–50 nm thickness, while for stoichiometric Au–WO3−x films, Au percentage higher than 40% will lead to a narrow SPR dip for high resolution SPR gas sensing. For Ag–WO3−x nanocomposite films, higher metal percentage and thinner thickness are required to achieve similar sharpness of the SPR dips as that for Au–WO3−x composite films. Our results indicated that the Au–WO3−x and Ag–WO3−x nanocomposite thin films with 40–80% metal fractions and film thickness of 30–50 nm are applicable for optical gas sensing.