Showing papers on "Resonance published in 2010"

The Fano resonance in plasmonic nanostructures and metamaterials

Abstract: Since its discovery, the asymmetric Fano resonance has been a characteristic feature of interacting quantum systems. The shape of this resonance is distinctively different from that of conventional symmetric resonance curves. Recently, the Fano resonance has been found in plasmonic nanoparticles, photonic crystals, and electromagnetic metamaterials. The steep dispersion of the Fano resonance profile promises applications in sensors, lasing, switching, and nonlinear and slow-light devices.

Investigation of Active Damping Approaches for PI-Based Current Control of Grid-Connected Pulse Width Modulation Converters With LCL Filters

Abstract: This paper deals with various active damping approaches for PI-based current control of grid-connected pulsewidth-modulation (PWM) converters with LCL filters, which are based on one additional feedback. Filter capacitor current, as well as voltage feedback for the purpose of resonance damping, are analyzed and compared. Basic studies in the continuous Laplace domain show that either proportional current feedback or derivative voltage feedback yields resonance damping. Detailed investigations of these two approaches in the discrete z-domain, taking into account the discrete nature of control implementation, sampling, and PWM, are carried out. Several ratios of LCL resonance frequency and control frequency are considered. At high resonance frequencies, only current feedback stabilizes the system. At medium resonance frequencies, both approaches have good performance. At low resonance frequencies, stability gets worse, even though voltage feedback offers slightly better damping properties. Measurements validate the theoretical results.

Spin determination of single-produced resonances at hadron colliders

Abstract: We study the production of a single resonance at the LHC and its decay into a pair of Z bosons. We demonstrate how full reconstruction of the final states allows us to determine the spin and parity of the resonance and restricts its coupling to vector gauge bosons. Full angular analysis is illustrated with the simulation of the production and decay chain including all spin correlations and the most general couplings of spin-zero, -one, and -two resonances to Standard Model matter and gauge fields. We note implications for analysis of a resonance decaying to other final states.

Coupling of Optical Resonances in a Compositionally Asymmetric Plasmonic Nanoparticle Dimer

Abstract: Electromagnetic coupling between plasmon resonant nanoparticles follows principles of molecular hybridization, that is, particle plasmons hybridize to form a lower energy bonding plasmon mode and a higher energy antibonding plasmon mode. For coupling between equivalent particles (homodimer), the in-phase mode is optically allowed, whereas the out-of-phase mode is dark due to the cancellation of the equivalent dipole moments. We probe, using polarized scattering spectroscopy, the coupling in a pair of nonequivalent particles (silver/gold nanoparticle heterodimer) that allows us to observe both in-phase and out-of-phase plasmon modes. The hybridization model postulates that the bonding modes should be red shifted with respect to the gold particle plasmon resonance and the antibonding modes blue shifted with respect to the silver particle plasmon resonance. In practice, the antibonding modes are red shifted with respect to the silver plasmon resonance. This anomalous shift is due to the coupling of the silve...

Electromagnetic fields distribution in multilayer thin film structures and the origin of sensitivity enhancement in surface plasmon resonance sensors

Abstract: The performance of surface plasmon resonance (SPR) sensors depends on the design parameters. An algorithm for calculating the electromagnetic fields distribution in multilayer structure is developed relying on Abeles matrices method for wave propagation in isotropic stratified media. The correlation between field enhancement and sensitivity enhancement is examined and found to agree with the overlap integral in the analyte region. This correlation was verified in the conventional SPR sensor based on Kretschmann configuration, and in the improved SPR sensor with high refractive index dielectric top layer for several cases, e.g. field enhancement due to resonance, the sensitivity dependence on the wavelength, the influence of prism refractive index on sensitivity, and the effect of the layers materials and thicknesses.

Tuning the resonance in high-temperature superconducting terahertz metamaterials.

Abstract: In this Letter, we present resonance properties in terahertz metamaterials consisting of a split-ring resonator array made from high-temperature superconducting films. By varying the temperature, we observe efficient metamaterial resonance switching and frequency tuning. The results are well reproduced by numerical simulations of metamaterial resonance using the experimentally measured complex conductivity of the superconducting film. We develop a theoretical model that explains the tuning features, which takes into account the resistive resonance damping and additional split-ring inductance contributed from both the real and imaginary parts of the temperature-dependent complex conductivity. The theoretical model further predicts more efficient resonance tuning in metamaterials consisting of a thinner superconducting split-ring resonator array, which are also verified in subsequent experiments.

Normal-state spin dynamics and temperature-dependent spin-resonance energy in optimally doped BaFe 1.85 Co 0.15 As 2

Abstract: A neutron scattering study reveals that the magnetic fluctuations in an iron arsenide superconductor behave according to the conventional theories of metals, unlike the cuprate superconductors. Moreover, the magnetic spin-excitation energies are sufficient to mediate the Cooper pairs that form the superconducting state.

Damping of nanomechanical resonators.

Abstract: We study the transverse oscillatory modes of nanomechanical silicon nitride strings under high tensile stress as a function of geometry and mode index $m\ensuremath{\le}9$. Reproducing all observed resonance frequencies with classical elastic theory we extract the relevant elastic constants. Based on the oscillatory local strain we successfully predict the observed mode-dependent damping with a single frequency-independent fit parameter. Our model clarifies the role of tensile stress on damping and hints at the underlying microscopic mechanisms.

Measuring the local pressure amplitude in microchannel acoustophoresis

Abstract: A new method is reported on how to measure the local pressure amplitude and the Q factor of ultrasound resonances in microfluidic chips designed for acoustophoresis of particle suspensions. The method relies on tracking individual polystyrene tracer microbeads in straight water-filled silicon/glass microchannels. The system is actuated by a PZT piezo transducer attached beneath the chip and driven by an applied ac voltage near its eigenfrequency of 2 MHz. For a given frequency a number of particle tracks are recorded by a CCD camera and fitted to a theoretical expression for the acoustophoretic motion of the microbeads. From the curve fits we obtain the acoustic energy density, and hence the pressure amplitude as well as the acoustophoretic force. By plotting the obtained energy densities as a function of applied frequency, we obtain Lorentzian line shapes, from which the resonance frequency and the Q factor for each resonance peak are derived. Typical measurements yield acoustic energy densities of the order of 10 J/m3, pressure amplitudes of 0.2 MPa, and Q factors around 500. The observed half wavelength of the transverse acoustic pressure wave is equal within 2% to the measured width w = 377 μm of the channel.

Resonance type non-contact charging apparatus

Abstract: A resonance type non-contact charging system is disclosed that includes a resonance system. The resonance system has a primary side resonance coil, a secondary side resonance coil, a power converting section having a DC/DC converter, and a battery. The charging system has a controlling section that controls the DC/DC converter. The controlling section controls the duty cycle of the DC/DC converter such that the input impedance of the resonance system at the resonant frequency and the output impedance of a high-frequency power source match each other.

A selectively coated photonic crystal fiber based surface plasmon resonance sensor

Abstract: We propose a novel design for a photonic crystal fiber based surface plasmonic resonance sensor. The sensor consists of selectively metal-coated air holes containing analyte channels, which enhance the phase matching between the plasmonic mode and the core-guided mode. Good refractive index sensitivity as high as 5500 nm/RIU (refractive index unit) can be achieved in the proposed structure. Compared with the entirely coated structure, the selectively coated sensor design demonstrates narrower resonance spectral width. Moreover, the greater resonance depth can improve the sensing performance in terms of signal to noise ratio (SNR). The improvements in spectral width and SNR can both contribute to a better detection limit for this refractive index sensor.

Confinement-Induced Resonances in Low-Dimensional Quantum Systems

Abstract: We report on the observation of confinement-induced resonances in strongly interacting quantum-gas systems with tunable interactions for one- and two-dimensional geometry. Atom-atom scattering is substantially modified when the s-wave scattering length approaches the length scale associated with the tight transversal confinement, leading to characteristic loss and heating signatures. Upon introducing an anisotropy for the transversal confinement we observe a splitting of the confinement-induced resonance. With increasing anisotropy additional resonances appear. In the limit of a two-dimensional system we find that one resonance persists.

Strongly coupled quantum dot-metal nanoparticle systems: Exciton-induced transparency, discontinuous response, and suppression as driven quantum oscillator effects

Abstract: We probe the transition to bistability that exists in a hybrid metal nanoparticle and semiconductor quantum dot (SQD) system when they are strongly coupled. In particular, we see a discontinuous jump in the response of the system (in both the diagonal and off-diagonal density-matrix elements) and a SQD response that is highly suppressed above resonance in this transition region. This discontinuous response and suppression arise because the SQD acts as a driven (quantum) oscillator. The phase change at resonance drastically alters the hybrid response when crossing the resonance. The study of this transition region, the discontinuity, and the suppression phenomena provides different insights into understanding this system, predicts a more complicated behavior than previously thought and corrects earlier work where the transition region was absent.

Observing Plasmonic−Molecular Resonance Coupling on Single Gold Nanorods

Abstract: Strong plasmonic-molecular resonance coupling occurs between noble metal nanocrystals and organic adsorbates when the plasmonic resonance is degenerate with the molecular one. This interaction forms the basis for many fundamental studies and practical applications. We describe here the first direct measurement of the resonance coupling on single gold nanorods. The dark-field scattering technique is employed. The nanorods are embedded in hydrogel to facilitate uniform dye adsorption. The adsorbed dye molecules exhibit both monomer and H-aggregate absorption bands. The same gold nanorods are measured before and after the dye adsorption. Both strong and weak Coupling are investigated by selecting nanorods with different longitudinal plasmon bands. Excellent agreement between the experiments and an analytic theory is obtained. The resonance coupling reveals a unique three-band structure, The tunability of the coupling on individual nanorods is further demonstrated by photodecomposing the adsorbed dye molecules.

Influence of Particle-Substrate Interaction on Localized Plasmon Resonances

Abstract: We present a theory for determining the localized surface plasmon resonance shifts of arbitrarily shaped metal nanoparticles on a substrate. Using a pseudoparticle concept, an expression for the particle-substrate interaction is derived, providing both physical insight and formulas to estimate the shifted plasmon resonance. The theory is verified against measured scattering spectra of nanorods on substrates. Simple formulas are provided to calculate the resonance of nanorods, spheres, and ellipsoids on dielectric substrate.

Plasmon-induced magneto-optical activity in nanosized gold disks.

Abstract: In this Letter we show that nanostructures made out of pure noble metals can exhibit measurable magneto-optic activity at low magnetic fields. This phenomenon occurs when the localized surface plasmon resonance of the nanostructure is excited in the presence of a static magnetic field parallel to the propagation of incident light. The large magneto-optical response observed comes from an increase of the magnetic Lorentz force induced by the large collective movement of the conduction electrons in the nanostructures when the resonance is excited.

Controlling phase separation of binary Bose-Einstein condensates via mixed-spin-channel Feshbach resonance

Abstract: We investigate controlled phase separation of a binary Bose-Einstein condensate in the proximity of a mixed-spin-channel Feshbach resonance in the $|F=1,{m}_{F}=+1\ensuremath{\rangle}$ and $|F=2,{m}_{F}=\ensuremath{-}1\ensuremath{\rangle}$ states of $^{87}\mathrm{Rb}$ at a magnetic field of 9.10 G. Phase separation occurs on the lower-magnetic-field side of the Feshbach resonance while the two components overlap on the higher-magnetic-field side. The Feshbach resonance curve of the scattering length is obtained from the shape of the atomic cloud by comparison with the numerical analysis of coupled Gross-Pitaevskii equations.

Multipolar plasmon resonances in individual ag nanorice.

Abstract: We study the optical excitation of high-order surface plasmon resonance modes in individual Ag nanorice particles using dark-field scattering spectroscopy. We analyze the results by model calculations using the boundary element method. Symmetry breaking caused by oblique illumination makes the even order resonance modes observable in the optical spectrum. All the resonance peaks are found to redshift with increasing length of the particle.

Symmetry breaking and strong coupling in planar optical metamaterials

Abstract: We demonstrate narrow transmission resonances at near-infrared wavelengths utilizing coupled asymmetric split-ring resonators (SRRs). By breaking the symmetry of the coupled SRR system, one can excite dark (subradiant) resonant modes that are not readily accessible to symmetric SRR structures. We also show that the quality factor of metamaterial resonant elements can be controlled by tailoring the degree of asymmetry. Changing the distance between asymmetric resonators changes the coupling strength and results in resonant frequency tuning due to resonance hybridization.

High quality factor metallodielectric hybrid plasmonic-photonic crystals

Abstract: A 2D polystyrene colloidal crystal self-assembled on a flat gold surface supports multiple photonic and plasmonic propagating resonance modes. For both classes of modes, the quality factors can exceed 100, higher than the quality factor of surface plasmons (SP) at a polymer–gold interface. The spatial energy distribution of those resonance modes are carefully studied by measuring the optical response of the hybrid plasmonic–photonic crystal after coating with dielectric materials under different coating profiles. Computer simulations with results closely matching those of experiments provide a clear picture of the field distribution of each resonance mode. For the SP modes, there is strong confinement of electromagnetic energy near the metal surface, while for optical modes, the field is confined inside the spherical particles, far away from the metal. Coating of dielectric material on the crystal results in a large shift in optical features. A surface sensor based on the hybrid plasmonic–photonic crystal is proposed, and it is shown to have atomic layer sensitivity. An example of ethanol vapor sensing based on physisorption of ethanol onto the sensor surface is demonstrated.

Basic study of improving efficiency of wireless power transfer via magnetic resonance coupling based on impedance matching

Abstract: Wireless power transfer is essential for the spread of Electric Vehicle(EV) usage as it provides a safe and convenient way to charge the EVs. Recently, a highly efficient mid-range wireless power transfer technology using electromagnetic resonance coupling, WiTricity, was proposed. Studies show that the resonant frequencies of the two antennas change according to the air gap in between the antennas. To achieve maximum efficiency using this system, the resonance frequencies of the antennas and the frequency of the system has to be matched. However, when this technology is applied in the MHz range (which allows small sized antennas), the usable frequency is bounded by the Industrial, Scientific, and Medical(ISM) band. Hence a method to fix the resonance frequency within the ISM band is required. In this paper, the possibility of using impedance matching (IM) networks to adjust the resonance frequency of a pair of antennas at a certain distance to 13.56MHz is studied. We studied the electrical characteristics of the antenna with equivalent circuits, electromagnetic analysis and experiments. The equivalent circuits are used as reference to calculate the parameters of the IM circuits. The simulations and experiments shows that the IM circuits can change the resonance frequency to 13.56MHz for different air gaps, thus improving the power transfer efficiency.

Quantitative evaluation of electromagnetic enhancement in surface-enhanced resonance Raman scattering from plasmonic properties and morphologies of individual Ag nanostructures

Abstract: The electromagnetic (EM) enhancement in surface-enhanced resonance Raman scattering (SERRS) is quantitatively evaluated for rhodamine molecules adsorbed on Ag nanostructures. Polarization dependence of the plasma resonance (plasmon resonance) and the SERRS spectra from single isolated Ag nanostructures was evaluated to determine one-to-one relationship between optical anisotropy of plasma resonance, that of SERRS, and the morphology of the nanostructures. Experimental observations were compared with finite-difference time-domain calculations of the EM field induced by plasma resonance using individual morphology of the nanostructures. The experimental enhancement factor of SERRS $\ensuremath{\sim}{10}^{9}$ was consistent with that of the calculations within a factor of $\ensuremath{\sim}2$ for three excitation wavelengths. We conclusively fortify the indispensible importance of SERRS-EM theory with our results to design metal nanostructures generating strong EM enhancement.

Optical properties of metal-dielectric-metal microcavities in the THz frequency range.

Abstract: We present an experimental and theoretical study of the optical properties of metal-dielectric-metal structures with patterned top metallic surfaces, in the THz frequency range. When the thickness of the dielectric slab is very small with respect to the wavelength, these structures are able to support strongly localized electromagnetic modes, concentrated in the subwavelength metal-metal regions. We provide a detailed analysis of the physical mechanisms which give rise to these photonic modes. Furthermore, our model quantitatively predicts the resonance positions and their coupling to free space photons. We demonstrate that these structures provide an efficient and controllable way to convert the energy of far field propagating waves into near field energy.

Direct observation of mode-coupling instability in two-dimensional plasma crystals.

Abstract: Dedicated experiments on melting of two-dimensional plasma crystals were carried out. The melting was always accompanied by spontaneous growth of the particle kinetic energy, suggesting a universal plasma-driven mechanism underlying the process. By measuring three principal dust-lattice wave modes simultaneously, it is unambiguously demonstrated that the melting occurs due to the resonance coupling between two of the dust-lattice modes. The variation of the wave modes with the experimental conditions, including the emergence of the resonant (hybrid) branch, reveals exceptionally good agreement with the theory of mode-coupling instability.

Plasmonically induced transparent magnetic resonance in a metallic metamaterial composed of asymmetric double bars.

Abstract: We demonstrate that the trapped magnetic resonance mode can be induced in an asymmetric double-bar structure for electromagnetic waves normally incident onto the double-bar plane, which mode otherwise cannot be excited if the double bars are equal in length. By adjusting the structural geometry, the trapped magnetic resonance becomes transparent with little resonance absorption when it happens in the dipolar resonance regime, a phenomenon so-called plasmonic analogue of electromagnetically induced transparency (EIT). This planar EIT-like metamaterial offers a great geometry simplification by combining the radiant and subradiant resonant modes in a single double-bar resonator.

Disentangling the dynamical origin of P11 nucleon resonances.

Abstract: The dynamical origins of the two poles associated with the Roper resonance are examined. Both of them together with the next higher resonance in the P11 partial wave are found to have the same originating bare state, indicating that the coupling to the meson-baryon continuum induces multiple observed resonances from the same bare state. Concerning other partial waves, the resonance poles extracted within the same multi-channels multi-resonances model of pi N reactions are compared to those listed by the Particle Data Group (PDG). Within our reaction model, all the identified resonances consist of a core state and meson-baryon components.

Resonance lineshapes in two-dimensional Fourier transform spectroscopy

Abstract: We derive an analytical form for resonance lineshapes in two-dimensional (2D) Fourier transform spectroscopy. Our starting point is the solution of the optical Bloch equations for a two-level system in the 2D time domain. Application of the projection-slice theorem of 2D Fourier transforms reveals the form of diagonal and cross-diagonal slices in the 2D frequency data for arbitrary inhomogeneity. The results are applied in quantitative measurements of homogeneous and inhomogeneous broadening of multiple resonances in experimental data.

Positive Frequency Shifts Observed Upon Adsorbing Micron-Sized Solid Objects to a Quartz Crystal Microbalance from the Liquid Phase

Abstract: By specifically binding derivatized colloidal particles and physisorbing nonderivatized particles to the surface of a quartz crystal microbalance (QCM), we have observed positive shifts of frequency, Δf, in contrast to the negative frequency shifts typically found in adsorption experiments. Evidently, the Sauerbrey relation does not apply to this situation. A comparison of frequencies shifts and bandwidths on different overtones reveals a coupled resonance: at low overtones, Δf is negative, whereas it is positive at high overtones, with maximal resonance bandwidth observed at the crossover point. As predicted by the Dybwad model,(1) the spheres bound to the surface form resonating systems on their own. A composite resonator is formed, consisting of a large crystal with resonance frequency ω and the adsorbed spheres with resonance frequency ωS. In the case in which the resonance frequency of the small spheres (firmly attached to crystal), ωS, is higher than the resonance frequency of the crystal, ω, Δf of ...

Tunable humidity sensor based on ITO-coated optical fiber

Abstract: Here, it is presented the fabrication and characterization of a new tunable humidity sensor based on ITO-coated optical fiber. A thin nanostructurated multilayer polymeric film sensitive to humidity is deposited onto the ITO layer. The device is characterized by means of a resonance in the infrared region. Resonance wavelength variations of 600 nm have been recorded during the multilayer fabrication process. The thickness of the polymeric coating was adjusted to operate on the point of maximum variation of the resonance wavelength per refractive index unit (RIU) in order to take advantage of the high sensitivity of these resonance based devices. The precise thickness control was achieved by using the layer-by-layer (LbL) deposition technique. The quality of the device is proved experimentally with a sensitivity improvement of a factor four if the tuned optical fiber sensor is used instead of the non-tuned one.