Linear nonstationary optical dimensional resonances in atomic nanostructures

The existence of linear nonstationary optical resonances in a diatomic nanostructural object with a dipole-dipole atomic interaction has been proved. A new solution to the joint system of modified Bloch optical equations and nonlocal field equations is obtained for time intervals much shorter than the times of phase and energy relaxation. Formulas for effective polarizabilities of the object’s atoms, which have a set of dimensional resonances, are derived. The frequencies of these resonances significantly differ from the eigenfrequencies of the object’s atoms, and their properties depend on the interatomic distance, light-pulse duration, initial atomic inversions, and the orientation of the object’s axis relative to the direction of incidence of the external light wave.     

Optical size resonances in nanostructures

The existence of optical size resonances in atomic nanostructures is proved. The properties of optical size resonances strongly depend on the interatomic distances and on the polarization of an external radiation field. The properties of linear and nonlinear size resonances are considered in the case of two-dimensional nanostructures. The linear optical size resonances are described based on a closed system of equations for dipole oscillators and nonlocal field equations taking into account the dipole-dipole interactions of atoms in the radiation field. Using a stationary solution to these equations, it is demonstrated that two isotropic atoms with definite intrinsic frequencies form an anisotropic system in the radiation field, possessing two or four size resonances depending on whether the component atoms are identical or different. The nanostructure composed of two different atoms possesses two size resonances with positive dispersion and two other resonances with negative dispersion. The frequencies of the size resonances significantly differ from the intrinsic frequencies of isolated atoms entering into the nanostructure. By changing the angle of incidence of the external wave, it is possible to excite various size resonances. The properties of nonlinear optical size resonances excited by an intense radiation field were theoretically and numerically studied using the modified Bloch equations and nonlocal field equations. Dispersion relationships for the nonlinear resonances were derived and the inversion properties of atoms in the nanostructure were studied for various polarizations of the external optical wave.     

Interplay of plasmon resonances in binary nanostructures

By introducing the difference permittivity ratio η=(ε ₂?ε ₀)/(ε ₁?ε ₀), the Green matrix method for computing surface plasmon resonances is extended to binary nanostructures. Based on the near field coupling, the interplay of plasmon resonances in two closely packed nanostrips is investigated. At a fixed wavelength, with varying η the resonances exhibit different regions: the dielectric effect region, resonance chaos region, collective resonance region, resonance flat region, and new branches region. Simultaneously, avoiding crossing and mode transfer phenomena between the resonance branches are observed. These findings will be helpful to design hybrid plasmonic subwavelength structures.     

Shape-dependent plasmon resonances of Ag nanostructures

Different silver nanostructures have been rapidly synthesized under microwave irradiation from a solution of silver nitrate (AgNO₃) and β$\beta$-D glucose; neither additional reducing nor capping agent were required in this soft green solution approach. Not only spherical nanoparticles, but also necklace and wires have been synthesized. The plasmon resonances of the synthesized silver nanostructures were tuned by varying the irradiation time and hence by changing size and morphology of nanostructures. The obtained nanostructures were characterized by X-Ray diffraction (XRD), Uv–Vis spectroscopy (Uv–Vis), transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM). The change of peak position and the shape of the absorption spectra were clearly observed during the whole reaction process; in fact, it was evidenced that initially Ag nanoparticles were formed, which, as reaction time elapsed, self-assembled and fused with each other to yield nanowires.     

Dark-line atomic resonances in submillimeter structures

We present measurements of dark-line resonances excited in cesium atoms confined in submillimeter cells with a buffer gas. The width and contrast of the resonances were measured for cell lengths as low as 100 microm. The measured atomic Q factors are reduced in small cells because of frequent collisions of atoms with the cell walls. However, the contrast of coherent population trapping resonances measured in the small cells is similar in magnitude to that obtained in centimeter-sized cells, but substantially more laser intensity is needed to excite the resonance fully when increased buffer-gas pressure is used. The effect of the higher intensity on the linewidth is reduced because the intensity broadening rate decreases with buffer-gas pressure.     

Nonlinear resonances of contact photoionization in heterogeneous nanostructures

A theory of nonlinear interference effects is constructed for a heterogeneous charge transfer between atoms in polycrystalline films or heterogeneous nanostructures of the semiconductor-insulator type, which interact with resonance radiation, and a metallic contact surface. The probability of resonance contact photoionization in heterogeneous solid nanostructures is determined, which makes it possible to use this process in nanotechnologies and nonlinear information systems. Nonlinear resonances of contact photoionization are asymmetric due to interference of a radiative transition to an excited state and a transition to the continuum induced by the metal surface. The probability of resonance contact photoionization abruptly decreases with increasing distance between an atom in the semiconductor and the metal.     

Hydrogen maser atomic beam resonances

Au^? ions at anionic places are formed in gold doped crystals by a reducing treatment withF centers. The ultraviolet absorption consists of 4 bands, which are namedA, B, C, andD in analogy to the isoelectronic centers of the s² type, like Tl⁺. TheB band oszillator strength strongly increases with temperature in accordance with a phonon allowed transition. The ratio of the dipole strength of theC band to that of theA band as a function of the relative position of theB band is compared with Suganos prediction. Zero phonon lines are found at helium temperatures for theA band in NaCl (2,985 Å), KCl (3,068 Å), and KBr (3,145 Å) and for theC band in KCl (2,329 Å). In KCl the Huang-Rhys factor isg=3.4 for theA band. The vibronic structure comes from the relatively large radius 6s ² state of the negative ion. Uniaxial stress splits the zero phonon line. The results definitely agree with the stress splitting behaviour of a degenerateΓ ₁→Γ ₄ transition. Inversion symmetry of the center is confirmed by the absence of a linear Stark effect.     

人工光学微结构研究进展

受益于新世纪以来微纳加工技术的快速发展,人工光学微结构的相关研究在近二十年里取得了长足进步。人工光学微结构集合了光学介观体系丰富的物理机理、有力的光参量调控手段,为实现对光与物质相互作用的有效操控提供了一种全新的方式,为光学器件的小型化、集成化和轻质化提供了新的途径。文章将对人工光学微结构这些年的发展进行概述,并展示该研究领域的最新研究进展。     

Multiple Fano resonances in nanorod and nanoring hybrid nanostructures

Multiple Fano resonances of plasmonic nanostructures have attracted much attention due to their potential applications in multicomponent biosensing. In this paper, we propose a series of hybridized nanostructures consisting of a single nanoring and multiple nanorods to generate multiple Fano resonances. One to three Fano resonances are achieved through tuning the number of nanorods. The interaction coupling process between different components of the nanostructures is recognized as the mechanism of multiple Fano resonances. We also theoretically investigate the applications of the produced multiple Fano resonances in refractive index sensing. The specific properties of multiple Fano resonances will make our proposed nanostructures beneficial to high-sensitivity biosensors.     

Parallel fabrication of atomic nanostructures

A new approach to fabrication of atomic nanostructures for atomic nanooptics is reported, which is based on the use of one-, two-, and three-dimensional spatial localization of laser fields at the nanoscale level, and fabrication of atomic nanostructures on a surface is demonstrated.     

Multimode resonances in square-shaped optical microcavities

Square-shaped two-dimensional optical microcavities (micro-cavities) were investigated for possible applications as filters for dense wavelength-division multiplexing. Multimode cavity resonances were observed in the elastic scattering of approximately 200-microm square-shaped micro-cavities in fused silica. Based on a two-dimensional k-space representation, we accounted for the multimode spectrum by different normal modes with rays confined by total internal reflection. The cavity-mode trajectories need not be closed after each round trip. Single-mode spectra are expected from smaller square-shaped micro-cavities.     

Nonlinear dynamics of giant resonances in atomic nuclei

The dynamics of monopole giant resonances in nuclei is analyzed in the time-dependent relativistic mean-field model. The phase spaces of isoscalar and isovector collective oscillations are reconstructed from the time series of dynamical variables that characterize the proton and neutron density distributions. The analysis of the resulting recurrence plots and correlation dimensions indicates regular motion for the isoscalar mode, and chaotic dynamics for the isovector oscillations. Information-theoretic functionals identify and quantify the nonlinear dynamics of giant resonances in quantum systems that have spatial as well as temporal structure.     

Boundary-value problems in near-field optical microscopy and optical size resonances

We have solved a boundary-value problem for a ball probe interacting with a flat dielectric surface in an external optical radiation field. This interaction gives rise to the optical size resonance at frequencies significantly different from the natural frequencies of two-level atoms both in the medium and in the probe with allowance for the local field corrections. These resonances depend significantly on the distance from the probe center to the surface, on the ball probe size, on the concentration of two-level atoms in the probe and in the medium, on the spectral line width, and on the atomic inversion. The field strengths inside and outside the ball probe and a semiinfinite dielectric medium have been calculated in the near-field and wave zones. It is shown that the proposed electrodynamic theory of optical near-field microscopy agrees with the results of experimental measurements.     

Broadening of Cr nanostructures in laser-focused atomic deposition

This paper presents the experimental progress of laser-focused Cr atomic deposition and the experimental condition.The result is an accurate array of lines with a periodicity of 212.8±0.2 nm and mean full-width at half maximum as approximately 95 nm.Surface growth in laser-focused Cr atomic deposition is modeled and studied by kinetic Monte Carlo simulation including two events:the one is that atom trajectories in laser standing wave are simulated with the semiclassical equations of motion to obtain the deposition position;the other is that adatom diffuses by considering two major diffusion processes,namely,terrace diffusion and step-edge descending.Comparing with experimental results(Anderson W R,Bradley C C,McClelland J J and Celotta R J 1999 Phys.Rev.A 59 2476),it finds that the simulated trend of dependence on feature width is in agreement with the power of standing wave,the other two simulated trends are the same in the initial stage.These results demonstrate that some surface diffusion processes play important role in feature width broadening.Numerical result also shows that high incoming beam flux of atoms deposited redounds to decrease the distance between adatoms which can diffuse to minimize the feature width and enhance the contrast.     

Grating resonances in air-silica microstructured optical fibers

We report what is believed to be the first demonstration of optical fiber gratings written in photonic crystal fibers. The fiber consists of a germanium-doped photosensitive core surrounded by a hexagonal periodic air-hole lattice in a silica matrix. The spectra of these gratings allow for a detailed characterization of the fiber. In particular, the gratings facilitate coupling to higher-order leaky modes. We show that the spatial distribution and the effective index of these modes are determined largely by the design of the lattice and that the grating spectra are unaffected by the refractive index surrounding the fiber. We describe these measurements and corresponding simulations and discuss their implications for the understanding of such air-hole structures.     

Defect-induced whispering-gallery-mode resonances in optical microdisk resonators

In this Letter we present results of theoretical and experimental studies of whispering-gallery modes in optical microdisk resonators interacting with subwavelength dielectric particles. We predict theoretically and confirm by direct observations that, contrary to the generally accepted models, both peaks of the particle-induced doublet of resonances are redshifted with respect to the position of the initial resonance.     

End and central plasmon resonances in linear atomic chains

The existence and nature of end and central plasmon resonances in a linear atomic chain, the 1D analog to surface and bulk plasmons in 2D metals, has been predicted by ab initio time-dependent density functional theory. Length dependence of the absorption spectra shows the emergence and development of collectivity of these resonances. It converges to a single resonance in the longitudinal mode, and two transverse resonances, which are localized at the ends and center of the atom chains. These collective modes bridge the gaps, in concept and scale, between the collective excitation of atomic physics and nanoplasmonics. It also outlines a route to atomic-scale engineering of collective excitations.     

Engineering the electromagnetic properties of periodic nanostructures using electrostatic resonances

Electromagnetic properties of periodic two-dimensional subwavelength structures consisting of closely packed inclusions of materials with negative dielectric permittivity epsilon in a dielectric host with positive epsilon(h) can be engineered using the concept of multiple electrostatic resonances. Fully electromagnetic solutions of Maxwell's equations reveal multiple wave propagation bands, with the wavelengths much longer than the nanostructure period. Some of these bands are described using the quasistatic theory of the effective dielectric permittivity epsilon(qs). Those bands exhibit multiple cutoffs and resonances which are found to be related to each other through a duality condition. An additional propagation band characterized by a negative magnetic permeability is found. Imaging with subwavelength resolution in that band is demonstrated.