Dipole Resonance Mode Research Articles

LOW LOSS METAL DIPLEXER AND COMBINER BASED ON A PHOTONIC BAND GAP CHANNEL-DROP FILTER AT 109 GHZ

In this paper, we present the design, fabrication and measurements for a W-band metal Photonic Band Gap (PBG) Channel-Drop Filter (CDF) diplexer, which can also be employed as a combiner to combine signals of difierent frequencies into a single waveguide. A PBG CDF is a device that allows channeling of a selected frequency from a continuous spectrum into a separate waveguide through resonant defects in a PBG structure. A PBG CDF transmits straight through all the frequencies except for the resonant frequency, and thus it represents a diplexer. Reversing the wave ∞ow directions causes it to combine signals of difierent frequencies from two difierent waveguides into a single channel, representing a combiner. The device is compact and conflgurable and can be employed for mm-wave spectrometry with applications in communications, radio astronomy, and radar receivers for remote sensing and nonproliferation. High ohmic losses in metals constitute the main challenge in realization of a metal CDF at W-band. To mitigate the problem of ohmic losses, the fllter was designed to operate at coupled dipole resonant modes instead of coupled fundamental monopole modes. The experimental samples were fabricated in two difierent ways: by conventional machining and by electroforming. The comparative results of the samples' testing are presented in the paper. Frequency selectivity of 30dB with a 0.3GHz linewidth at 108.5GHz was demonstrated. In addition, we suggest an experimental method to check the frequencies of separate resonant cavities of fabricated samples which do not properly operate and a possible way to adjust the geometry of the cavities for the frequencies to meet the required speciflcations.

Influence of spherical anisotropy on the optical properties of plasmon resonant metallic nanoparticles

We demonstrate the features of the dipole and quadrupole resonant modes in extinction spectra of spherically anisotropic nanoparticles based on full-wave scattering theory. It is found that in a core–shell nanosphere, the introduction of spherical anisotropy in the core leads to a blue shift in resonant wavelengths for small nanoparticles, while, for large nanoparticles (core radius larger than 90 nm), the dipole resonant wavelength remains unchanged with the variation of spherical anisotropy. In addition, the peak strengths for the dipole and quadrupole modes are also studied. Numerical simulations show that the strong localization of electric fields can be further enhanced and tuned by adjusting the spherical anisotropy in the core. In contrast, the anisotropy introduced in the shell results in a blue shift for small nanoparticles but a red shift for nanoparticles with larger size. The tunability of plasmon resonant shifts in extinction spectra and tailored localization of enhanced fields are revealed.

Integrable equations for the model with N sources and n-1 modes

We consider simplified models of coupling charged matter to radiation resonance modes generalizing the well-known Jaynes-Cummings and Dicke models. We find that these new models are integrable for arbitrary numbers of dipole sources and resonance modes of the radiation field. We discuss the problem of explicitly diagonalizing the corresponding Hamiltonians.

Correlation between helical surface waves and guided modes of an infinite immersed elastic cylinder

Scattering of obliquely incident plane acoustic waves from immersed infinite solid elastic cylinders is a complex phenomenon that involves generation of various types of surface waves on the body of the cylinder. Mitri [F.G. Mitri, Acoustic backscattering enhancement resulting from the interaction of an obliquely incident plane wave with an infinite cylinder, Ultrasonics 50 (2010) 675–682] recently showed that for a solid aluminum cylinder, there exist acoustic backscattering enhancements at a normalized frequency of ka ⩽ 0.1 . The incidence angle α c at which these enhancements are observed lies between the first (longitudinal) and second (shear) coupling angles of the cylinder. He also confirmed the observations previously reported by the authors that there exist backscattering enhancements of the dipole mode at large angles of incidence where no wave penetration into the cylinder is expected. In this paper, physical explanations are provided for the aforementioned observations by establishing a correlation between helical surface waves generated by oblique insonification of an immersed infinite solid elastic cylinder and the longitudinal and flexural guided modes that can propagate along the cylinder. In particular, it is shown that the backscattering enhancement observed at ka ⩽ 0.1 is due to the excitation of the first longitudinal guided mode travelling at the bar velocity along the cylinder. It is also demonstrated that the dipole resonance mode observed at incidence angles larger than the Rayleigh coupling angle is associated with the first flexural guided mode of the cylinder. The correlation established between the scattering and propagation problems can be used in both numerical and experimental studies of interaction of mechanical waves with cylinders.

Acoustic backscattering enhancements resulting from the interaction of an obliquely incident plane wave with an infinite cylinder

Background and objective The analysis of the acoustic backscattering enhancements from tilted cylinders is of particular importance in determining some of the (visco)elastic properties of the cylinder, and/or its surrounding fluid in ultrasonic non-destructive evaluation (NDE) and imaging (NDI) applications. Previous related investigations on an aluminum cylinder limited to incidence angles varying from 0° to 40°, revealed the existence of an anomalous “pseudo-Rayleigh” mode (above the critical Rayleigh angle) identified as the rigid-body translational dipole ( n = 1) mode. The objective here is to provide a complete investigation on the backscattering enhancements for incidence angles larger than 40° for various elastic and viscoelastic cylinder materials. Method Using the partial-wave series solution for the linear scattering by an infinite circular cylinder, the acoustic backscattering from isotropic elastic and viscoelastic (polymer-type) cylinders excited by an obliquely incident plane acoustic wave is investigated. Total and resonance backscattering form functions are calculated for several elastic and viscoelastic cylinder materials immersed in water versus the angle of incidence 0° ⩽ α < 90°. The “pure” resonance peaks are isolated by subtracting a rigid background from the total form function, so the associated resonance modes are properly identified. Results and conclusion The plots of the partial-wave series reveal acoustic backscattering enhancements (not shown in previous investigations) generally occurring at ka ≲ 0.1 at a critical angle α c bounded by the longitudinal and shear waves coupling angles θ L = sin - 1 ( c / c L ) and θ S = sin - 1 ( c / c S ) such that θ L < α c < θ S (where c L and c S are the phase velocities of the longitudinal and shear waves inside the elastic cylinder, and c is the speed of sound in the surrounding medium). It is shown here that the backscattering enhancements with a critical angle θ L < α c < θ S result from the excitation of the monopole ( n = 0) resonance mode. Moreover, additional acoustic backscattering enhancements still occur in the range 1 ≲ ka ≲ 6 even though the angle of tilt is greater than the Rayleigh wave coupling angle θ R = sin - 1 ( c / c R ) (where c R is the Rayleigh wave velocity in an elastic half-space). The resonance scattering theory shows that such additional enhancements are associated with the excitation of a dipole ( n = 1) resonance mode which may result from the interference of meridional and/or helical waves propagating along the cylinder’s surface. It is therefore essential to consider tilt angles ranging from normal to end-on incidence for a complete analysis of the backscattering by elastic and viscoelastic cylinders.

A High-Gain Antenna Consisting of Two Slot Elements With a Space Larger Than a Wavelength

In standard antenna array, high grating-lobe caused by large space between elements would degrade antenna performance, and in this letter, we propose a corrugated two-slots array with a space larger than a wavelength in the E-plane, which can realize high radiation performance. A corrugated structure is loaded between slot elements as the secondary radiation source, and this slot source is based on slot dipole resonance mode to keep a low profile. Simulated and measured results both show high grating-lobe level drastically suppressed to less than -10 dB with the introduction of the corrugated grooves, compared to the case of flat two-slot array without grooves. Additionally, the antenna gain is significantly increased by about 9 dB, and half-power beamwidth (HPBW) in both E- and H-plane are narrowed as well. This letter is also considered as a reply to Appl. Phys. Lett., vol. 93, pp. 156101, Oct. 2008.

Comparison of Resonant Plasmon Polaritons with Mie Scattering for Laser-Induced Near-Field Nanopatterning: Metallic Particle vs Dielectric Particle

In this paper we describe a comparative study of near-field surface nanopatterning using metallic and dielectric nanoparticles excited by an 820 nm near-infrared femtosecond laser. It is found that the existing understanding that a metallic particle generates a larger near-field than a dielectric particle when the particle size is smaller than the illumination wavelength is NOT always correct. Concerning near-field enhancement on low-refractive-index substrates, the enhancement factor for an appropriate dielectric particle in the TE1 (magnetic dipole) resonance mode is found to be higher than that induced by a gold particle even in the TM1 (electric dipole) resonance mode of a gold particle. Conversely, on a high-refractive-index substrate such as silicon, the near-field enhancement factor is larger using a gold particle with the same particle size. This result will be useful for selecting the best combination of substrate and nanoparticle material for laser-induced nanoparticle-mediated optical near-field patterning.

Localized surface plasmon resonance enhanced photoluminescence of CdSe QDs in PMMA matrix on silver colloids with different shapes

Localized surface plasmon resonance (LSPR) enhanced photoluminescences (PL) from CdSe quantum dots (QDs) on worm-like or quasi-spherical silver colloids have been investigated. The shape of silver colloid film is controlled by annealing temperature (200 °C∼350 °C). Strong PL enhancements of CdSe QDs on both as-grown and annealed silver colloid films are observed. The results show that the PL enhancement factor of CdSe QDs on worm-like silver colloid film reaches as high as 15-fold. Moreover, the enhancement factor is 5 times larger than that obtained from the quasi-spherical silver colloids. The superiority of worm-like silver nanostructure on LSPR enhanced photoluminescence is attributed to its larger size, hot spots and multiple dipole resonance modes coupling, which are induced by aggregation effect.

Optical Properties of Spherical and Oblate Spheroidal Gold Shell Colloids

The surface plasmon modes of spherical and oblate spheroidal core-shell colloids composed of a 312 nm diameter silica core and a 20 nm thick Au shell are investigated. Large arrays of uniaxially aligned core shell colloids with size aspect ratios ranging from 1.0 to 1.7 are fabricated using a novel ion irradiation technique. Angle- and polarization-resolved extinction spectroscopy is performed on the arrays. Extinction spectra on spherical particles reveal dipole, quadrupole, and octupole resonances in good agreement with calculations using Mie theory. Optical extinction measurements on oblate spheroidal core-shell show strong red- and blue-shifts for polarizations along major and minor axes, respectively, that increase with size anisotropy. The measured spectral shifts of the dipole, quadrupole, and octupole resonant modes with angle and anisotropy are in good agreement with T-matrix calculations. The data provide insight into the tunable resonant behavior of surface plasmons in oblate spheroidal core-shell particles.

Low-energy dipole excitations in nuclei at the N = 50, 82 and Z = 50 shell closures as signatures for a neutron skin

Low-energy dipole excitations have been investigated theoretically in N = 5088Sr and 90Zr, several N = 82 isotones and the Z = 50 Sn isotopes. For this purpose a method incorporating both HFB and multi-phonon QPM theory is applied. A concentration of one-phonon dipole strength located below the neutron emission threshold has been calculated in these nuclei. The analysis of the corresponding neutron and proton dipole transition densities allows us to assign a genuine pattern to the low-energy excitations and make them distinct from the conventional GDR modes. Analyzing also the QRPA wave functions of the states we can identify these excitations as pygmy dipole resonance (PDR) modes, recently studied also in Sn and N = 82 nuclei. The results for N = 50 are exploratory for an experimental project designed for the bremsstrahlung facility at the ELBE accelerator.

Integrable Models of Interaction of Matter with Radiation

The simplified models of interaction of charged matter with resonance modes of radiation generalizing the well-known Jaynes-Cummings and Dicke models are considered. It is found that these new models are integrable for arbitrary numbers of dipole sources and resonance modes of the radiation field. The problem of explicit diagonalisation of corresponding Hamiltonians is discussed.

Large amplitude dynamics of clusters and nuclet

We discuss and compare the dipole resonance modes in nuclei and metal clusters under varying conditions: different excitation mechanisms in the case of nuclei, changed back-ground structure in the case of clusters. The resonances are generally nicely harmonic modes, even those with a large amplitude. Only extreme shapes, as they occur in fusion and fission, can perturb this harmonicity.

Nonlinear dynamics of nuclei and metal clusters

We discuss and compare dipole resonance modes in nuclei and metal clusters. In both systems, we observe well-developed collectivity with harmonic oscillations which persist high up into the regime of multiple resonances. Deformations tend to induce spectral fragmentation. In clusters, these effects are hardly strong enough to destroy all collectivity, except for the extreme of a fissioning cluster. Nuclear surface modes, on the other hand, are found to interfere strongly with the giant resonances being able to dissolve them completely.

Generator coordinate description of the giant dipole and double giant dipole resonance of 16O and 40Ca

In the framework of the generator coordinate method (GCM), and utilizing an appropriate ansatz for the generator states and an effective many-body Skyrme interaction, we derive analytically the collective Hamiltonians for the giant dipole resonance mode of 16O and 40Ca. The eigenfunctions, eigenvalues and relevant physical quantities are obtained. The collective spectra are analysed and the GCM results for 40Ca are compared with pion double-charge-exchange data for the double giant dipole resonance.

Angular and polarization dependence of surface-enhanced Raman scattering in attenuated-total-reflection geometry.

Polarization and angle-of-incidence dependences of the surface-enhanced Raman scattering (SERS) signal of benzoic acid adsorbed on isolated oblate particles of silver have been measured in an attenuated-total-reflection geometry. Simultaneously, the absorption of photons in the particles has been determined by a photoacoustic method. At the critical angle and in the wavelength range of the present study, only one dipole resonance mode, the nonazimuthally symmetric mode, is excited by the component of the electric field parallel to the reflecting surface. This has allowed us to evaluate contributions of the resonance absorption and the nonresonant intrinsic absorption to the total absorption. We show that the absorption of p-polarized light at the critical angle is solely due to the intrinsic absorption. No Raman signal can be detected in the absence of the surface-plasmon mode or electromagnetic resonance. We show also that the dependence of SERS on the polarization and angle of incidence can be explained by considering only the excitation of localized plasmons.

Virtual excitation of the GDR mode in the subbarrier23Na(p, ?)24Mg reaction

Differential cross sections for nonresonant radiative capture of low energy protons (E p = 1,348 keV and 1,370 keV) by23Na nuclei exhibit features pointing to the virtual excitation of the giant dipole resonance (GDR) mode. Theoretical analysis carried out within the framework of the direct — semidirect capture model reveals an enhanced coupling of the GDR with the incident protonf-wave consistent with the microscopic structure of the GDR in thes-d shell nuclei.

Nuclear Shape at High Spin and Excitation Energy

High-energy gamma rays from the deexcitation of giant dipole resonance modes have been measured for the decay of /sup 108/Sn and /sup 166/Er. The structure of the observed resonances can be correlated with the shapes of these nuclei at high excitation energy (E(approx. =60 MeV). For the deformed system /sup 166/Er a shape change with increasing temperature is suggested.

High energy gamma decay from newly formed compound states

Gamma rays associated with the decay of giant dipole resonance (GDR) modes and emitted in competition with the first evaporated particle from the compound system 166Er ∗ have been isolated by a difference technique. It is found that the measured gamma ray yield from the very highest excitation energy populated in the reaction, accounts for ≈ 25% of the total gamma ray cross section for transition energies in the range 10–20 MeV, and this agrees well with the prediction of the statistical model for compound nuclear decay.

Resonances of rectangular dielectric cylinders

Numerical data are presented for the lowest monopole, dipole and quadrupole resonant modes of a dielectric rectangular cylinder. The data consist of a few typical field plots, together with curves for the resonant wavenumber, the quality factor, the dipole moment and the quadrupole dyadic.

Resonances of rectangular dielectric cylinders

Numerical data are presented for the lowest monopole, dipole and quadrupole resonant modes of a dielectric rectangular cylinder. The data consist of a few typical field plots, together with curves for the resonant wavenumber, the quality factor, the dipole moment and the quadrupole dyadic.