Showing papers on "Resonance published in 2012"

Magnetic light

Abstract: Spherical silicon nanoparticles with sizes of a few hundreds of nanometers represent a unique optical system According to theoretical predictions based on Mie theory they can exhibit strong magnetic resonances in the visible spectral range The basic mechanism of excitation of such modes inside the nanoparticles is very similar to that of split-ring resonators, but with one important difference that silicon nanoparticles have much smaller losses and are able to shift the magnetic resonance wavelength down to visible frequencies We experimentally demonstrate for the first time that these nanoparticles have strong magnetic dipole resonance, which can be continuously tuned throughout the whole visible spectrum varying particle size and visually observed by means of dark-field optical microscopy These optical systems open up new perspectives for fabrication of low-loss optical metamaterials and nanophotonic devices

Demonstration of Magnetic Dipole Resonances of Dielectric Nanospheres in the Visible Region

Abstract: Strong resonant light scattering by individual spherical Si nanoparticles is experimentally demonstrated, revealing pronounced resonances associated with the excitation of magnetic and electric modes in these nanoparticles. It is shown that the low-frequency resonance corresponds to the magnetic dipole excitation. Due to high permittivity, the magnetic dipole resonance is observed in the visible spectral range for Si nanoparticles with diameters of ∼200 nm, thereby opening a way to the realization of isotropic optical metamaterials with strong magnetic responses in the visible region.

Surface plasmon enhanced absorption and suppressed transmission in periodic arrays of graphene ribbons

Abstract: Resonance diffraction in the periodic array of graphene microribbons is theoretically studied following a recent experiment [L. Ju et al., Nature Nanotech. 6, 630 (2011)]. Systematic studies over a wide range of parameters are presented. It is shown that a much richer resonant picture would be observable for higher relaxation times of charge carriers: More resonances appear and transmission can be totally suppressed. The comparison with the absorption cross-section of a single ribbon shows that the resonant features of the periodic array are associated with leaky plasmonic modes. The longest-wavelength resonance provides the highest visibility of the transmission dip and has the strongest spectral shift and broadening with respect to the single-ribbon resonance, due to collective effects.

Experimental and theoretical studies on MEMS piezoelectric vibrational energy harvesters with mass loading

Abstract: Experimental and theoretical investigations on micro-scale multi-morph cantilever piezoelectric vibrational energy harvesters (PZEHs) of the MicroElectroMechanical Systems (MEMS) are presented. The core body of a PZEH is a “multi-morph” cantilever, where one end is clamped to a base and the other end is free. This “fixed-free” cantilever system including a proof-mass (also called the end-mass) on the free-end that can oscillate with the multi-layer cantilever under continuous sinusoidal excitations of the base motion. A partial differential equation (PDE) describing the flexural wave propagating in the multi-morph cantilever is reviewed. The resonance frequencies of the lowest mode of a multi-morph cantilever PZEH for some ratios of the proof-mass to cantilever mass are calculated by either solving the PDE numerically or using a lumped-element model as a damped simple harmonic oscillator; their results are in good agreement (disparity ≤ 0.5%). Experimentally, MEMS PZEHs were constructed using the standard micro-fabrication technique. Calculated fundamental resonance frequencies, output electric voltage amplitude V and output power amplitude P with an optimum load compared favorably with their corresponding measured values; the differences are all less than 4%. Furthermore, a MEMS PZEH prototype was shown resonating at 58.0 ± 2.0 Hz under 0.7 g ( g = 9.81 m/s 2 ) external excitations, corresponding peak power reaches 63 μW with an output load impedance Z of 85 kΩ. This micro-power generator enabled successfully a wireless sensor node with the integrated sensor, radio frequency (RF) radio, power management electronics, and an advanced thin-film lithium-ion rechargeable battery for power storage at the 2011 Sensors Expo and Conference held in Chicago, IL. In addition, at 58 Hz and 0.5, 1.0 g excitations power levels of 32, and 128 μW were also obtained, and all these three power levels demonstrated to be proportional to the square of the acceleration amplitude as predicted by the theory. The reported P at the fundamental resonance frequency f 1 and acceleration G -level, reached the highest “Figure of Merit” [power density × (bandwidth/resonant frequency)] achieved amongst those reported in the up-to-date literature for high quality factor Q f MEMS PZEH devices.

Experimental observation of dissipative soliton resonance in an anomalous-dispersion fiber laser

Abstract: We have experimentally observed conventional solitons and rectangular pulses in an erbium-doped fiber laser operating at anomalous dispersion regime. The rectangular pulses exhibit broad quasi-Gaussian spectra (~40 nm) and triangular autocorrelation traces. With the enhancement of pump power, the duration and energy of the output rectangular pulses almost increase linearly up to 330 ps and 3.2 nJ, respectively. It is demonstrated that high-energy pulses can be realized in anomalous-dispersion regime, and may be explained as dissipative soliton resonance. Our results have confirmed that the formation of dissipative soliton resonance is not sensitive to the sign of cavity dispersion.

Wireless power transmission system, and method of controlling resonance impedance and resonance frequency of wireless power transmission system

Abstract: A wireless power transmission system, and a method for controlling a resonance impedance and a resonance frequency of the wireless power transmission system are provided. According to one aspect, a wireless power transmitter may include: a power generator configured to generate tracking power using a resonance frequency, the tracking power being used for a resonance frequency tracking; a source resonator configured to transmit the tracking power to a target resonator; a mismatching detector configured to detect a mismatching between the target resonator and the source resonator; and a controller configured to adjust the resonance frequency, or an impedance of a repeater resonator when the mismatching is detected, the repeater resonator being used to perform an impedance matching between the target resonator and the source resonator.

Blueshift of the surface plasmon resonance in silver nanoparticles studied with EELS

Abstract: We study the surface plasmon (SP) resonance energy of isolated spherical Ag nanoparticles dispersed on a silicon nitride substrate in the diameter range 3.5-26 nm with monochromated electron energy-loss spectroscopy. A significant blueshift of the SP resonance energy of 0.5 eV is measured when the particle size decreases from 26 down to 3.5 nm. We interpret the observed blueshift using three models for a metallic sphere embedded in homogeneous background material: a classical Drude model with a homogeneous electron density profile in the metal, a semiclassical model corrected for an inhomogeneous electron density associated with quantum confinement, and a semiclassical nonlocal hydrodynamic description of the electron density. We find that the latter two models provide a qualitative explanation for the observed blueshift, but the theoretical predictions show smaller blueshifts than observed this http URL a homogeneous medium.

Surface plasmon resonances in periodic and random patterns of gold nano-disks for broadband light harvesting

Abstract: We analyze the localized surface plasmon resonance spectra of periodic square lattice arrays of gold nano-disks, and we describe numerically and experimentally the effect of disorder on resonance width, spectrum, and EM field enhancement in increasingly randomized patterns. The periodic structure shows a narrower and stronger extinction peak, conversely we observe an increase of up to (1-2)×10(2) times enhancement as the disorder is gradually introduced. This allows for simpler, lower resolution fabrication, cost-effective in light harvesting for solar cell and sensing applications. We show that dipole-dipole interactions contribute to diffract light parallel to the surface as a mean of long-range coupling between the nano-disks.

Tunable broad-band perfect absorber by exciting of multiple plasmon resonances at optical frequency

Abstract: A broad-band perfect absorber composing a two-dimensional periodic metal-dielectric-metal sandwiches array on dielectric/metal substrate is designed and numerically investigated. It is shown that the nearly-perfect absorption with a bandwidth of about 50 nm in visible region can be achieved by overlapping of two plasmon resonances: one originating from the coupling of electric dipoles between adjacent unit cells and another arising from magnetic dipole plasmon resonances. A capacitor-inductor circuit description is introduced to explain the dependence of resonance frequencies and band-width on geometrical parameters.

Electron spin resonance of nitrogen-vacancy centers in optically trapped nanodiamonds

Abstract: Using an optical tweezers apparatus, we demonstrate three-dimensional control of nanodiamonds in solution with simultaneous readout of ground-state electron-spin resonance (ESR) transitions in an ensemble of diamond nitrogen-vacancy color centers. Despite the motion and random orientation of nitrogen-vacancy centers suspended in the optical trap, we observe distinct peaks in the measured ESR spectra qualitatively similar to the same measurement in bulk. Accounting for the random dynamics, we model the ESR spectra observed in an externally applied magnetic field to enable dc magnetometry in solution. We estimate the dc magnetic field sensitivity based on variations in ESR line shapes to be approximately . This technique may provide a pathway for spin-based magnetic, electric, and thermal sensing in fluidic environments and biophysical systems inaccessible to existing scanning probe techniques.

Structure of High-Resolution NMR Spectra

Abstract: Structure of High-Resolution NMR Spectra provides the principles, theories, and mathematical and physical concepts of high-resolution nuclear magnetic resonance spectra. The book presents the elementary theory of magnetic resonance; the quantum mechanical theory of angular momentum; the general theory of steady state spectra; and multiple quantum transitions, double resonance and spin echo experiments.

The theory of surface-enhanced Raman scattering.

Abstract: By considering the molecule and metal to form a conjoined system, we derive an expression for the observed Raman spectrum in surface-enhanced Raman scattering. The metal levels are considered to consist of a continuum with levels filled up to the Fermi level, and empty above, while the molecule has discrete levels filled up to the highest occupied orbital, and empty above that. It is presumed that the Fermi level of the metal lies between the highest filled and the lowest unfilled level of the molecule. The molecule levels are then coupled to the metal continuum both in the filled and unfilled levels, and using the solutions to this problem provided by Fano, we derive an expression for the transition amplitude between the ground stationary state and some excited stationary state of the molecule-metal system. It is shown that three resonances contribute to the overall enhancement; namely, the surface plasmon resonance, the molecular resonances, as well as charge-transfer resonances between the molecule and metal. Furthermore, these resonances are linked by terms in the numerator, which result in SERS selection rules. These linked resonances cannot be separated, accounting for many of the observed SERS phenomena. The molecule-metal coupling is interpreted in terms of a deformation potential which is compared to the Herzberg-Teller vibronic coupling constant. We show that one term in the sum involves coupling between the surface plasmon transition dipole and the molecular transition dipole. They are coupled through the deformation potential connecting to charge-transfer states. Another term is shown to involve coupling between the charge-transfer transition and the molecular transition dipoles. These are coupled by the deformation potential connecting to plasmon resonance states. By applying the selection rules to the cases of dimer and trimer nanoparticles we show that the SERS spectrum can vary considerably with excitation wavelength, depending on which plasmon and/or charge-transfer resonance is excited.

Figure-of-merit enhancement of surface plasmon resonance sensors in the spectral interrogation

Abstract: We show that adding a thin dielectric layer with high refractive index on top of the metallic layer in surface plasmon resonance sensors in the Kretschmann–Raether configuration in the spectral mode causes a redshift of the resonance wavelength, narrowing of the resonance dip, and an enhancement to the spectral sensitivity. Surprisingly, together with the sensitivity enhancement, the dip becomes much narrower and the figure of merit is considerably improved, particularly in the IR range.

Pushing the Sample-Size Limit of Infrared Vibrational Nanospectroscopy: From Monolayer toward Single Molecule Sensitivity

Abstract: While scattering-scanning near-field optical microscopy (s-SNOM) has demonstrated its potential to extend infrared (IR) spectroscopy into the nanometer scale, it has not yet reached its full potential in terms of spectroscopic sensitivity. We combine broadband femtosecond mid-IR excitation with an optimized spectral irradiance of ∼2 W/cm(2)/ cm(-1) (power/area/bandwidth) and a combination of tip- and substrate enhancement to demonstrate single-monolayer sensitivity with exceptional signal-to-noise ratio. Using interferometric time domain detection, the near-field IR s-SNOM spectral phase directly reflects the molecular vibrational resonances and their intrinsic line shapes. We probe the stretching resonance of ∼1000 carbonyl groups at 1700 cm(-1) in a self-assembled monolayer of 16-mercaptohexadecanoic acid (MHDA) on an evaporated gold substrate with spectroscopic contrast and sensitivity of ≲100 vibrational oscillators. From these results we provide a roadmap for achieving true single-molecule IR vibrational spectroscopy in s-SNOM by implementing optical antenna resonant enhancement, increased spectral pump power, and improved detection schemes.

Towards the production of ultracold ground-state RbCs molecules: Feshbach resonances, weakly bound states, and the coupled-channel model

Abstract: We have studied interspecies scattering in an ultracold mixture of ${}^{87}$Rb and ${}^{133}$Cs atoms, both in their lowest-energy spin states. The three-body loss signatures of 30 incoming $s$- and $p$-wave magnetic Feshbach resonances over the range 0 to 667 G have been cataloged. Magnetic field modulation spectroscopy was used to observe molecular states bound by up to 2.5 $\text{MHz}\ifmmode\times\else\texttimes\fi{}h$. We have created RbCs Feshbach molecules using two of the resonances. Magnetic moment spectroscopy along the magnetoassociation pathway from 197 to 182 G gives results consistent with the observed and calculated dependence of the binding energy on magnetic field strength. We have set up a coupled-channel model of the interaction and have used direct least-squares fitting to refine its parameters to fit the experimental results from the Feshbach molecules, in addition to the Feshbach resonance positions and the spectroscopic results for deeply bound levels. The final model gives a good description of all the experimental results and predicts a large resonance near 790 G, which may be useful for tuning the interspecies scattering properties. Quantum numbers and vibrational wave functions from the model can also be used to choose optimal initial states of Feshbach molecules for their transfer to the rovibronic ground state using stimulated Raman adiabatic passage.

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.

Valley–spin blockade and spin resonance in carbon nanotubes

Abstract: The bandgap of a low-disorder, bent carbon nanotube is exploited to achieve Pauli blockade and spin resonance.

Sub-diffraction thin-film sensing with planar terahertz metamaterials

Abstract: Planar metamaterials consisting of subwavelength resonators have been recently proposed for thin dielectric film sensing in the terahertz frequency range. Although the thickness of the dielectric film can be very small compared with the wavelength, the required area of sensed material is still determined by the diffraction-limited spot size of the terahertz beam excitation. In this article, terahertz near-field sensing is utilized to reduce the spot size. By positioning the metamaterial sensing platform close to the sub-diffraction terahertz source, the number of excited resonators, and hence minimal film area, are significantly reduced. As an additional advantage, a reduction in the number of excited resonators decreases the inter-cell coupling strength, and consequently the resonance Q factor is remarkably increased. The experimental results show that the resonance Q factor is improved by more than a factor of two compared to the far-field measurement. Moreover, for a film with a thickness of λ/375 the minimal area can be as small as 0.2λ × 0.2λ. The success of this work provides a platform for future metamaterial-based sensors for biomolecular detection.

Resonance captures and targeted energy transfers in an inertially-coupled rotational nonlinear energy sink

Abstract: We explore the conservative and dissipative dynamics of a two-degree-of-freedom (2-DoF) system consisting of a linear oscillator and a lightweight nonlinear rotator inertially coupled to it. When the total energy of the system is large enough, the motion of the rotator is, generically, chaotic. Moreover, we show that if the damping of the rotator is sufficiently small and the damping of the linear oscillator is even smaller, then the system passes through a cascade of resonance captures (transient internal resonances) as the total energy gradually decreases. Rather unexpectedly, all these captures have the same principal frequency but correspond to different nonlinear normal modes (NNMs). In each NNM, the rotator is phase-locked into periodic motion with two frequencies. The NNMs differ by the ratio of these frequencies, which is approximately an integer for each NNM. Essentially non-integer ratios lead to incommensurate periods of ‘slow’ and ‘fast’ motions of the rotator and, thus, to its chaotic behavior between successive resonance captures. Furthermore, we show that these cascades of resonance captures lead to targeted energy transfer (TET) from the linear oscillator to the rotator, with the latter serving, in essence, as a nonlinear energy sink (NES). Since the inertially-coupled NES that we consider has no linearized natural frequency, it is capable of engaging in resonance with the linear oscillator over broad frequency and energy ranges. The results presented herein indicate that the proposed rotational NES appears to be a promising design for broadband shock mitigation and vibration energy harvesting.

Theoretical limit of localized surface plasmon resonance sensitivity to local refractive index change and its comparison to conventional surface plasmon resonance sensor

Abstract: In this paper, the theoretical sensitivity limit of the localized surface plasmon resonance (LSPR) to the surrounding dielectric environment is discussed. The presented theoretical analysis of the LSPR phenomenon is based on perturbation theory. Derived results can be further simplified assuming quasistatic limit. The developed theory shows that LSPR has a detection capability limit independent of the particle shape or arrangement. For a given structure, sensitivity is directly proportional to the resonance wavelength and depends on the fraction of the electromagnetic energy confined within the sensing volume. This fraction is always less than unity; therefore, one should not expect to find an optimized nanofeature geometry with a dramatic increase in sensitivity at a given wavelength. All theoretical results are supported by finite-difference time-domain calculations for gold nanoparticles of different geometries (rings, split rings, paired rings, and ring sandwiches). Numerical sensitivity calculations based on the shift of the extinction peak are in good agreement with values estimated by perturbation theory. Numerical analysis shows that, for thin (≤10 nm) analyte layers, sensitivity of the LSPR is comparable with a traditional surface plasmon resonance sensor and LSPR has the potential to be significantly less sensitive to temperature fluctuations.

High propagating velocity of spin waves and temperature dependent damping in a CoFeB thin film

Abstract: Spin wave propagation in a magnetron-sputtered CoFeB thin film is investigated. We apply both in-plane and out-of-plane magnetic fields. At room temperature, we find velocities of up to 25 and 3.5 km/s, respectively. These values are much larger compared to a thin permalloy film. Analyzing the resonance linewidth, we obtain an intrinsic Gilbert damping parameter of about 0.007 at room temperature. It increases to 0.023 at 5 K. CoFeB is a promising material for magnonic devices supporting fast propagating spin waves.

Dual-Band Omnidirectional Circularly Polarized Antenna Using Zeroth- and First-Order Modes

Abstract: This letter discusses the development of a dual-band omnidirectional circularly polarized (CP) antenna using the zeroth- and the first-order resonance modes of epsilon-negative (ENG) transmission lines (TLs). The antenna is based on a circular mushroom structure with curved branches and designed without additional feeding parts for a 90 ° phase difference between two orthogonal modes as well as additional radiators for dual-band operations. A left-hand CP (LHCP) and a right-hand CP (RHCP) are obtained at the zeroth- and the first-order resonance modes, respectively, because the current direction of the curved branch, which is related to a horizontal polarization, at the zeroth-order resonance (ZOR) mode is opposite to that at the first-order resonance (FOR) mode. The measured average axial ratios at the resonance modes in the azimuthal plane are 1.57 and 0.86 dB, respectively. The measured average LHCP and RHCP gains are - 0.24 dBic at the ZOR mode and -0.51 dBic at the FOR mode, respectively. These results are congruent with simulated data.

Detecting external electron spins using nitrogen-vacancy centers

Abstract: Near-surface nitrogen-vacancy (NV) centers have been created in diamond through low-energy implantation of ${}^{15}$N to sense electron spins that are external to the diamond. By performing double resonance experiments, we have verified the presence of $g$ $=$ 2 spins on a diamond crystal that was subjected to various surface treatments, including coating with a polymer film containing the free radical 2,2-diphenyl-1-picrylhydrazyl. Subsequent acid cleaning eliminated the spin signal without otherwise disrupting the NV center, providing strong evidence that the spins were at the surface. A clear correlation was observed between the strength of the external spin signal and the relaxation time ${T}_{2}$ for the six NV centers studied. We have developed a model that takes into account the finite correlation time of the fluctuating magnetic fields generated by the external spins, and used it to infer the signal strength and correlation time of the magnetic fields from these spins. This model also highlights the sensitivity advantage of active manipulation of the longitudinal spin component via double resonance over passive detection schemes that measure the transverse component of spin.

Surface Phase Transitions in BiFeO3 Below Room Temperature

Abstract: We combine a wide variety of experimental techniques to analyze two heretofore mysterious phase transitions in multiferroic bismuth ferrite at low temperature. Raman spectroscopy, resonant ultrasound spectroscopy, electron paraelectric resonance, x-ray lattice constant measurements, conductivity and dielectric response, and specific heat and pyroelectric data have been collected for two different types of samples: single crystals and, in order to maximize surface/volume ratio to enhance surface phase transition effects, BiFeO${}_{3}$ nanotubes were also studied. The transition at $T$ $=$ 140.3 K is shown to be a surface phase transition, with an associated sharp change in lattice parameter and charge density at the surface. Meanwhile, the 201 K anomaly appears to signal the onset of glassy behavior.

Plasmonics of coupled graphene micro-structures

Abstract: The optical response of graphene micro-structures, such as micro-ribbons and discs, is dominated by the localized plasmon resonance in the far infrared spectral range. An ensemble of such structures is usually involved and the effect of the coupling between the individual structures is expected to play an important role. In this paper, plasmonic coupling of graphene micro-structures in different configurations is investigated. Whereas a relatively weak coupling between graphene discs on the same plane is observed, the coupling between vertically stacked graphene discs is strong and a drastic increase of the resonance frequency is demonstrated. The plasmons in a more complex structure can be treated as the hybridization of plasmons from more elementary structures. As an example, the plasmon resonances of graphene micro-rings are presented, in conjunction with their response in a magnetic field. Finally, the coupling of the plasmon and the surface polar phonons of SiO2 substrate is demonstrated by the observation of a new hybrid resonance peak around 500?cm?1.

Optical tuning and ultrafast dynamics of high-temperature superconducting terahertz metamaterials

Abstract: Through the integration of semiconductors or complex oxides into metal resonators, tunable metamaterials have been achieved by a change of environment using an external stimulus. Metals provide high conductivity to realize a strong resonant response in metamaterials; however, they contribute very little to the tunability. The complex conductivity in high-temperature superconducting films is highly sensitive to external perturbations, which provides new opportunities in achieving tunable metamaterials resulting directly from the resonant elements. Here we demonstrate ultrafast dynamical tuning of resonance in the terahertz (THz) frequency range in YBa_2Cu_3O_7-\delta (YBCO) split-ring resonator arrays excited by near-infrared femtosecond laser pulses. The photoexcitation breaks the superconducting Cooper pairs to create the quasiparticle state. This dramatically modifies the imaginary part of the complex conductivity and consequently the metamaterial resonance in an ultrafast timescale. We observed resonance switching accompanied with a wide range frequency tuning as a function of photoexcitation fluence, which also strongly depend on the nano-scale thickness of the superconducting films. All of our experimental results are well reproduced through calculations using an analytical model, which takes into account the SRR resistance and kinetic inductance contributed from the complex conductivity of YBCO films. The theoretical calculations reveal that the increasing SRR resistance upon increasing photoexcitation fluence is responsible for the reduction of resonance strength, and both the resistance and kinetic inductance contribute to the tuning of resonance frequency.

Magnetic plasmon induced transparency in three-dimensional metamolecules

Abstract: In a laser-driven atomic quantum system, a continuous state couples to a discrete state resulting in quantum interference that provides a transmission peak within a broad absorption profile the so-called electromagnetically induced transparency (EIT). In the field of plasmonic metamaterials, the subwavelength metallic structures play a role similar to atoms in nature. The interference of their near-field coupling at plasmonic resonance leads to a plasmon induced transparency (PIT) that is analogous to the EIT of atomic systems. A sensitive control of the PIT is crucial to a range of potential applications such as slowing light and biosensor. So far, the PIT phenomena often arise from the electric resonance, such as an electric dipole state coupled to an electric quadrupole state. Here we report the first three-dimensional photonic metamaterial consisting of an array of erected U-shape plasmonic gold nanostructures that exhibits PIT phenomenon with magnetic dipolar interaction between magnetic meta molecules. We further demonstrate using a numerical simulation that the coupling between the different excited pathways at an intermediate resonant wavelength allows for a pi phase shift resulting in a destructive interference. A classical RLC circuit was also proposed to explain the coupling effects between the bright and dark modes of EIT-like electromagnetic spectra. This work paves a promising approach to achieve magnetic plasmon devices.