Showing papers on "Resonance published in 2008"

A Unified Approach to Surface-Enhanced Raman Spectroscopy

Abstract: We present a unified expression for surface-enhanced Raman spectroscopy (SERS). The expression contains a product of three resonance denominators, representing the surface plasmon resonance, the metal-molecule charge-transfer resonance at the Fermi energy, and an allowed molecular resonance. This latter resonance is that from which intensity is borrowed for charge transfer, and when the molecular resonance is active it is responsible for surface-enhanced resonance Raman spectroscopy. We examine this expression in various limits, to explore the relative contribution or each resonance. First, we look at the situation in which only the surface plasmon resonance is active and examine the various contributions to the Raman signal, including the surface selection rules. Then we examine additional contributions from charge-transfer or molecular resonances. We show that the three resonances are not totally independent, since they are linked by a product of four matrix elements in the numerator. These linked matrix elements provide comprehensive selection rules for SERS. One involves a harmonic oscillator in the observed normal mode. This is the same mode which appears in the vibronic coupling operator linking one of the states of the allowed molecular resonance to the charge-transfer state. The charge-transfer transition moment is linked to the surface plasmon resonance by the requirement that the transition dipole moment be polarized along the direction of maximum amplitude of the field produced by the plasmon (i.e., perpendicular to the metal surface). We show that these selection rules govern the observed SERS spectral intensities and apply these to the observed spectra of several molecules. We also suggest a quantitative measure of the degree to which charge transfer contributes to the overall SERS enhancement.

A vibration energy harvesting device with bidirectional resonance frequency tunability

Abstract: Vibration energy harvesting is an attractive technique for potential powering of wireless sensors and low power devices. While the technique can be employed to harvest energy from vibrations and vibrating structures, a general requirement independent of the energy transfer mechanism is that the vibration energy harvesting device operate in resonance at the excitation frequency. Most energy harvesting devices developed to date are single resonance frequency based, and while recent efforts have been made to broaden the frequency range of energy harvesting devices, what is lacking is a robust tunable energy harvesting technique. In this paper, the design and testing of a resonance frequency tunable energy harvesting device using a magnetic force technique is presented. This technique enabled resonance tuning to ±20% of the untuned resonant frequency. In particular, this magnetic-based approach enables either an increase or decrease in the tuned resonant frequency. A piezoelectric cantilever beam with a natural frequency of 26 Hz is used as the energy harvesting cantilever, which is successfully tuned over a frequency range of 22‐32 Hz to enable a continuous power output 240‐280 μW over the entire frequency range tested. A theoretical model using variable damping is presented, whose results agree closely with the experimental results. The magnetic force applied for resonance frequency tuning and its effect on damping and load resistance have been experimentally determined. (Some figures in this article are in colour only in the electronic version)

Resonance energy transfer from a dye molecule to graphene

Abstract: We study the distance dependence of the rate of resonance energy transfer from the excited state of a dye to the \pi system of graphene. Using the tight-binding model for the \pi system and the Diraccone approximation, we obtain the analytic expression for the rate of energy transfer from an electronically excited dye to graphene. While in traditional fluorescence resonance energy transfer, the rate has a $(distance)^{-6}$ dependence, we find that the distance dependence in this case is quite different. Our calculation of rate in the case of the two dyes, pyrene and nile blue, shows that the distance dependence is Yukawa type. We have also studied the effect of doping on energy transfer to graphene. Doping does not modify the rate for electronic excitation energy transfer significantly. However, in the case of vibrational transfer, the rate is found to be increased by an order of magnitude due to doping. This can be attributed to the nonzero density of states at the Fermi level that results from doping.

Mapping the Plasmon Resonances of Metallic Nanoantennas

Abstract: We study the light scattering and surface plasmon resonances of Au nanorods that are commonly used as optical nanoantennas in analogy to dipole radio antennas for chemical and biodetection field-enhanced spectroscopies and scanned-probe microscopies. With the use of the boundary element method, we calculate the nanorod near-field and far-field response to show how the nanorod shape and dimensions determine its optical response. A full mapping of the size (length and radius) dependence for Au nanorods is obtained. The dipolar plasmon resonance wavelength I shows a nearly linear dependence on total rod length L out to the largest lengths that we study. However, L is always substantially less than I/2, indicating the difference between optical nanoantennas and long-wavelength traditional I/2 antennas. Although it is often assumed that the plasmon wavelength scales with the nanorod aspect ratio, we find that this scaling does not apply except in the extreme limit of very small, spherical nanoparticles. The plasmon response depends critically on both the rod length and radius. Large (500 nm) differences in resonance wavelength are found for structures with different sizes but with the same aspect ratio. In addition, the plasmon resonance deduced from the near-field enhancement can be significantly red-shifted due to retardation from the resonance in far-field scattering. Large differences in near-field and far-field response, together with the breakdown of the simple scaling law must be accounted for in the choice and design of metallic I/2 nanoantennas. We provide a general, practical map of the resonances for use in locating the desired response for gold nanoantennas.

Wireless power apparatus and methods

Abstract: Wireless energy transfer system. Antennas are maintained at resonance with High Q. Techniques of maintaining the high-Q resonance matching are disclosed.

Wireless Energy Transfer Using Coupled Antennas

Abstract: A power transmission system produces a magnetic field at a source that is wirelessly coupled to a receiver Both the source and receiver are capacitively coupled LC circuits, driven at or near resonance

Coherent thermal emission by excitation of magnetic polaritons between periodic strips and a metallic film.

Abstract: The present paper theoretically demonstrates coherent thermal emission in the infrared region by exciting magnetic polaritons between metallic gratings and an opaque metallic film, separated by a dielectric spacer. The coupling of the metallic strips and the film induces a magnetic response that is characterized by a negative permeability and positive permittivity. On the other hand, the metallic film intrinsically exhibits a negative permittivity and positive permeability in the near infrared. This artificial structure is equivalent to a pair of single-negative materials. By exciting surface magnetic polaritons, large emissivity peaks can be achieved at the resonance frequencies and are almost independent of the emission angle. The resonance frequency of the magnetic response can be predicted by an analogy to an inductor and capacitor circuit. The proposed structure can be easily constructed using micro/nanofabrication.

Nonlinear spectroscopy of photons bound to one atom

Abstract: Nonlinear optics traditionally involves macroscopic atomic ensembles or solid-state crystals. The observation of a nonlinear two-photon resonance in a system consisting of one single atom trapped inside an optical cavity demonstrates nonlinear optics at the level of individual quanta.

Cavity opto-mechanics

Abstract: Two device geometries that enable structural coexistence are micro-mechanical and optical resonators. In one geometry, a micro-cantilever mechanical resonator also functions as a mirror in a high-finesse optical cavity. In a second, opto-mechanical coexistence takes the form of a micron-scale silica toroid that exhibits both high-Q radio-frequency mechanical resonances and optical resonances.

High $Q$ -Factor In-Plane-Mode Resonant Microsensor Platform for Gaseous/Liquid Environment

Abstract: This paper presents a novel resonant-microsensor platform for chemical and biological sensing applications in gaseous and liquid environment. The disk-shape microstructure is operated in a rotational in-plane mode with typical resonance frequencies between 300 and 1000 kHz. By shearing the surrounding fluid instead of compressing it, damping is reduced, and high quality factors are achieved. The resonators feature electrothermal excitation elements and a piezoresistive Wheatstone bridge for detection, sensitive only to the in-plane rotational vibration mode. Microresonators with different dimensions have been fabricated and extensively characterized, achieving quality factors of up to 5800 in air. First tests performed in water after parylene coating show a Q factor of approximately 100. Short-term frequency stabilities obtained from Allan-variance measurements with 1-s gate time are as low as 1.2times10-8 in air and 2.3times10-6 in water. An analytical model describing the mechanical behavior of the disk resonators, represented by a simple harmonic oscillator, is derived. In particular, expression for the resonance frequency and quality factor of the disk resonators subject to air/liquid damping are proposed and compared with experimental results.

Sensitivity of Optical Fiber Sensor Based on Surface Plasmon Resonance: Modeling and Experiments

Abstract: In this paper, surface plasmon resonance curves of an optical fiber-based sensor were investigated. From an experimental and theoretical perspective, the response curves were analyzed and discussed. Precisely, such curves were calculated by modeling the analyte/metallic layer interface using a multilayer system, including the effects of roughness. Then, the experimental response curves observed in solutions with different refractive indices were compared to the simulated curves. Good agreement was obtained with respect to the resonance peak location and the shape of the curves. Consequently, these results enabled us to predict the ideal functioning conditions of the sensor, i.e., the working parameters corresponding to the best sensitivities of detection.

Surface-normal emission of a high-Q resonator using a subwavelength high-contrast grating.

Abstract: We report a novel high-quality (Q) factor optical resonator using a subwavelength high-contrast grating (HCG) with in-plane resonance and surface-normal emission. We show that the in-plane resonance is manifested is by a sharp, asymmetric lineshape in the surface-normal reflectivity spectrum. The simulated Q factor of the resonator is shown to be as high as 500,000. A HCG-resonator was fabricated with an InGaAs quantum well active region sandwiched in-between AlGaAs layers and a Q factor of >14,000 was inferred from the photoluminescence linewidth of 0.07 nm, which is currently limited by instrumentation. The novel HCG resonator design will serve as a potential platform for many devices including surface emitting lasers, optical filters, and biological or chemical sensors.

Direct observation of tetrahertz electromagnetic waves emitted from intrinsic Josephson junctions in single crystalline Bi2Sr2CaCu2O8+δ

Abstract: We have observed intense, coherent, continuous and monochromatic electromagnetic (EM) emission at terahertz frequencies generated from a single crystalline mesa structure of the high- T c superconductor Bi 2 Sr 2 CaCu 2 O 8+ δ intrinsic Josephson junction system. The mesa is fabricated by the Argon-ion-milling and photolithography techniques on the cleaved surface of Bi 2 Sr 2 CaCu 2 O 8+ δ single crystal. The frequency, ν , of the EM radiation observed from the sample obeys simple relations: ν = c / nλ = c /2 nw and ν = 2 eV / hN , where c is the light velocity in vacuum, n the refractive index of a superconductor, λ the wave length of the EM emission in vacuum, w the shorter width of the mesa, V the voltage applied to the mesa, N the number of layers of intrinsic Josephson junctions, e and h are the elementary charge and the Planck constant, respectively. These two relations strongly imply that the mechanism of the emission is, firstly, due to the geometrical resonance of EM waves to the mesa like a cavity resonance occuring in the mesa structure, and forming standing waves as cavity resonance modes, and secondly, due to the ac-Josephson effect, which works coherently in all intrinsic Josephson junctions. The peculiar temperature dependence of the power intensity emitted form samples shows a broad maximum in a temperature region between 20 and 40 K, suggesting that the nonequilibrium effect plays an essential role for the emission of EM waves in this system. The estimated total power is significantly improved in comparison with the previous report [L. Ozyuzer et al., Science 318 (2007) 1291, K. Kadowaki, et al., Physica C 437–438 (2006) 111, I.E. Batov, et al., Appl. Phys. Lett. 88 (2006) 262504], and reached as high as 5 μW from single mesa with w = 60 μm at 648 GHz, which enables us to use it for some of applications. So far, we succeeded in fabricating the mesa emitting EM waves up to 960 GHz in the fundamental mode in the w = 40 μm mesa, whereas the higher harmonics up to the 4-th order were observed, resulting in a frequency exceeding 2.5 THz. In sharp contrast to the previous reports [K. Kadowaki, et al., Physica C 437–438 (2006) 111 , M.-H. Bae, et al., Phys. Rev. Lett. 98, (2007) 027002], all the present measurements were done in zero magnetic field. Lastly, a plausible theoretical model for the mechanism of emission is discussed.

Non-contact wireless communication apparatus, method of adjusting resonance frequency of non-contact wireless communication antenna, and mobile terminal apparatus

Abstract: A non-contact wireless communication apparatus and a mobile terminal apparatus are provided. The non-contact wireless communication apparatus includes a non-contact wireless communication antenna, a resonance capacitor, connected in parallel with the non-contact wireless communication antenna, for obtaining a predetermined resonance frequency with the non-contact wireless communication antenna, a resonance frequency adjustment unit for changing a resonance capacitance of the resonance capacitor to adjust the resonance frequency, a capacitance change amount control unit for controlling a change in resonance capacitance of the resonance capacitor in the resonance frequency adjustment unit, a resonance frequency shift unit for shifting the resonance frequency of the non-contact wireless communication antenna, and on/off control unit for performing on/off control of the resonance frequency shift unit in accordance with the amount of change in resonance capacitance of the resonance capacitor by the capacitance variation control unit.

Vibrational Kondo effect in pure organic charge-transfer assemblies.

Abstract: A Kondo resonance has been observed using a scanning tunneling microscope on a single molecular layer of a purely organic charge-transfer salt grown on a metal surface. Analysis of the Kondo anomaly reveals that the electron acceptor of the film possesses a spin-$\frac{1}{2}$ ground state due to the localization of an unpaired electron in the conjugated lowest unoccupied molecular orbital. Because of the $\ensuremath{\pi}$ character of this molecular state the unpaired electron is strongly coupled to molecular vibrations, leading to the split of the Kondo resonance in vibrational sidebands.

Frequency Response Enhancement of Optical Injection-Locked Lasers

Abstract: The modulation response of injection-locked lasers has been carefully analyzed, theoretically and experimentally, with a focus on the strong optical injection regime. We derive closed-form solutions to the relaxation oscillation (resonance) frequency and damping term, as well as the low-frequency damping term, and discuss design rules for maximizing resonance frequency and broadband performance. A phasor model is described in order to better explain the enhancement of the resonance frequency. Experimental curves match closely to theory. Record resonance frequency of 72 GHz and broadband results are shown.

Contribution of electric quadrupole resonance in optical metamaterials

Abstract: Contribution of electric quadrupole resonance is studied in optical metamaterials through numerical simulation. For nanostructures, its radiation is often comparable to that from magnetic dipole. Their individual contributions can be determined by angle-resolved scattering spectroscopy.

Plasmon resonances in linear atomic chains: Free-electron behavior and anisotropic screening of d electrons

Abstract: Electronic excitations in linear atomic chains of simple and noble metals (silver) have been studied using time-dependent density-functional theory. The formation and development of collective resonances in the absorption spectra were obtained as functions of the chain length. A longitudinal collective resonance appears in both simple- and noble-metal chains. Its dispersion has been deduced and is compared with that of a one-dimensional electron gas. The transverse excitation generally shows a bimodal structure, which can be assigned as the ``end and central resonances.'' The $d$ electrons of silver atoms reduce both the energies and intensities of the transverse modes but have little effect on its longitudinal resonance. This anisotropic screening is determined by the interband $(d\ensuremath{\rightarrow}p)$ transition, which is involved only in transverse oscillations. Analysis of these results yields a general picture of plasmon resonances in one-dimensional atomic structures. Implications of such atomic-scale plasmons to surface plasmons in larger dimensions are also discussed.

Determination of coupling regime of high-Q resonators and optical gain of highly selective amplifiers

Abstract: We present a simple method to determine simultaneously the main characteristics of passive or active high-Q optical resonators. The method is based on cavity ringdown spectroscopy, where the probe wavelength is rapidly swept across the resonance. It has already been shown that this technique allows the loaded cavity lifetime of passive resonators to be obtained. We show that we can also infer the coupling regime for passive resonators and the resonant gain for active resonators. The method is tested on Er3+ doped fiber resonators and also applied to determine the intrinsic and external Q-factors of an MgF2 whispering gallery mode resonator.

Individual addressing of trapped ions and coupling of motional and spin states using RF radiation.

Abstract: Individual electrodynamically trapped and laser cooled ions are addressed in frequency space using radio-frequency radiation in the presence of a static magnetic field gradient. In addition, an interaction between motional and spin states induced by an rf field is demonstrated employing rf optical double resonance spectroscopy. These are two essential experimental steps towards realizing a novel concept for implementing quantum simulations and quantum computing with trapped ions.

Photonic crystal cavity based gas sensor

Abstract: We have studied the response of a photonic crystal cavity to changes of the ambient refractive index. Transmission measurements of the cavity under different gaseous environments and pressures showed a linear dependence of the resonance wavelength on the refractive index of the ambient gas. A change of the refractive index by 10−4 leads to a shift of the resonance by 8pm, which is readily detectable due to the high quality factor of the cavity. The observed wavelength shifts agree well with finite-difference time domain simulations of the cavity.

Active damping of LCL-filter resonance based on virtual resistor for PWM rectifiers — stability analysis with different filter parameters

Abstract: This publication presents the investigation of active damping of resonance oscillations with virtual resistor for grid-connected PWM rectifiers with LCL-filter for different filter parameters. Using the voltage-oriented PI current control with converter current feedback, additional active damping of the filter resonance is necessary for stable operation. In the literature different methods are proposed that differ in number of sensors and complexity of control algorithms. If higher damping of the switching ripple current is required LCL-filters with lower resonance frequencies can be used. Resulting low ratios between resonance frequency and control frequency challenge the control with respect to damping of resonance. Moreover, some active damping methods are not suitable for these filter settings. Here the active damping concept based on virtual resistor is analyzed concerning stability for two significant filter configurations. It turns out that it is applicable for configurations with higher resonance frequency, whereas systems lower resonance frequencies can poorly be damped. Additionally the method exhibits the advantage of simple implementation but the disadvantage of additional current sensors. Theoretical analyses and of the selected method with time-discrete implementation are shown in this paper. Theory is verified by experimental results.

Second-harmonic generation from complementary split-ring resonators

Abstract: We present experiments on second-harmonic generation from arrays of magnetic split-ring resonators and arrays of complementary split-ring resonators. In both cases, the fundamental resonance is excited by the incident femtosecond laser pulses under normal incidence, leading to comparably strong second-harmonic signals. These findings are discussed in terms of Babinet's principle and in terms of a recently developed microscopic classical theory that leads to good agreement regarding the relative and the absolute nonlinear signal strengths. The hydrodynamic convective contribution is found to be the dominant source of second-harmonic generation--in contrast to a previous assignment [Science 313, 502 (2006)].

In situ fabrication of Co90Nb10 soft magnetic thin films with adjustable resonance frequency from 1.3to4.9GHz

Abstract: In this work, we realized in situ fabricated Co90Nb10 soft magnetic thin films, with variable in-plane uniaxial magnetic anisotropy, without using the field induced method or postfabrication treatment. In situ control over the in-plane uniaxial magnetic anisotropy field, which varied from 1.6to22.7kAm−1, was achieved by adjusting the deposition oblique angle from 0° to 38°. As a consequence, the resonance frequencies of the films were continuously increased from 1.3to4.9GHz.

Multi-gap individual and coupled split-ring resonator structures.

Abstract: We present a systematic numerical study, validated by accompanied experimental data, of individual and coupled split ring resonators (SRRs) of a single rectangular ring with one, two and four gaps. We discuss the behavior of the magnetic resonance frequency, the magnetic field and the currents in the SRRs, as one goes from a single SRR to strongly interacting SRR pairs in the SRR plane. We show that coupling of the SRRs along the E direction results to shift of the magnetic resonance frequency to lower or higher values, depending on the capacitive or inductive nature of the coupling. Strong SRR coupling along propagation direction usually results to splitting of the single SRR resonance into two distinct resonances, associated with peculiar field and current distributions.

Mott-insulator States of ultracold atoms in optical resonators.

Abstract: We study the low temperature physics of an ultracold atomic gas in the potential formed inside a pumped optical resonator. Here, the height of the cavity potential, and hence the quantum state of the gas, depends not only on the pump parameters, but also on the atomic density through a dynamical ac-Stark shift of the cavity resonance. We derive the Bose-Hubbard model in one dimension and use the strong coupling expansion to determine the parameter regime in which the system is in the Mott-insulator state. We predict the existence of overlapping, competing Mott-insulator states, and bistable behavior in the vicinity of the shifted cavity resonance, controlled by the pump parameters. Outside these parameter regions, the state of the system is in most cases superfluid.

Voltage Control of the Resonance Frequency of Dielectric Electroactive Polymer (DEAP) Membranes

Abstract: We report on the characterization, active tuning, and modeling of the first mode resonance frequency of dielectric electroactive polymer (DEAP) membranes. Unlike other resonance frequency tuning techniques, the tuning procedure presented here requires no external actuators or variable elements. Compliant electrodes were sputtered or implanted on both sides of 20-35-mum-thick and 2-4-mm-diameter polydimethylsiloxane membranes. The electrostatic force from an applied voltage adds compressive stress to the membrane, effectively softening the device and reducing its resonance frequency, in principle to zero at the buckling threshold. A reduction in resonance frequency up to 77% (limited by dielectric breakdown) from the initial value of 1620 Hz was observed at 1800 V for ion-implanted membranes. Excellent agreement was found between our measurements and an analytical model we developed based on the Rayleigh-Ritz theory. This model is more accurate in the tensile domain than the existing model for thick plates applied to DEAPs. By varying the resonance frequency of the membranes (and, hence, their compliance), they can be used as frequency-tunable attenuators. The same technology could also allow the fine-tuning of the resonance frequencies in the megahertz range of devices made from much stiffer polymers.

H- Shaped Stacked Patch Antenna for Dual Band Operation

Abstract: Analysis of U-slot loaded patch stacked with H-shaped parasitic elements is given in this paper. It is found that the antenna exhibits dual resonance and both the resonance frequency (upper and lower) depends directly on slot width and inversely on slot length. Both upper and lower resonance frequency increase with increasing the value of h2. Typically the bandwidth at lower and upper resonance is found 3.66% and 10.25% respectively. The radiated power at higher frequency (beamwidth 64◦) is 0.73 dB as compared to lower resonance frequency (beamwidth 71◦). The theoretical results are compared with the simulated data obtained from IE3D.

Photon echoes generated by reversing magnetic field gradients in a rubidium vapor.

Abstract: We propose a photon echo quantum memory scheme using detuned Raman coupling to long-lived ground states. In contrast to previous three-level schemes based on controlled reversible inhomogeneous broadening that use sequences of π pulses, the scheme does not require accurate control of the coupling dynamics to the ground states. We present a proof-of-principle experimental realization of our proposal using rubidium atoms in a warm vapor cell. The Raman resonance line is broadened using a magnetic field that varies linearly along the direction of light propagation. Inverting the magnetic field gradient rephases the atomic dipoles and re-emits the light pulse in the forward direction.

Intense γ-Ray Source in the Giant-Dipole-Resonance Range Driven by 10-TW Laser Pulses

Abstract: A gamma-ray source with an intense component around the giant dipole resonance for photonuclear absorption has been obtained via bremsstrahlung of electron bunches driven by a 10-TW tabletop laser. 3D particle-in-cell simulation proves the achievement of a nonlinear regime leading to efficient acceleration of several sequential electron bunches per each laser pulse. The rate of the gamma-ray yield in the giant dipole resonance region (8