Semiclassical approach to surface plasmons in spheroidal clusters

The linearized Vlasov equation gives a semiclassical version of the random phase approximation. The solution of this equation is studied for electrons moving in a deformed equilibrium mean field which is approximated by a cavity of a spheroidal shape (both prolate and oblate). Contrary to spherical systems, there is a coupling between excitations of different multipolarity induced by the interaction between constituents. The dipole response presents a typical double-peaked profile with a strong dependence on the deformation. Presented by A. Dellafiore at the International Conference on “Atomic Nuclei and Metallic Clusters”, Prague, September 1–5, 1997.     

Near-field spectroscopy of surface plasmons in flat gold nanoparticles

We use near-field interference spectroscopy with a broadband femtosecond, white-light probe to study local surface plasmon resonances in flat gold nanoparticles (FGNPs). Depending on nanoparticle dimensions, local near-field extinction spectra exhibit none, one, or two resonances in the range of visible wavelengths (1.6-2.6 eV). The measured spectra can be accurately described in terms of interference between the field emitted by the probe aperture and the field reradiated by driven FGNP surface plasmon oscillations. The measured resonances are in good agreement with those predicted by calculations using discrete dipole approximation. We observe that the amplitudes of these resonances are dependent upon the spatial position of the near-field probe, which indicates the possibility of spatially selective excitation of specific plasmon modes.     

New approach to surface ionization and drift-tube spectroscopy of organic molecules

A new physical model of ionization of organic molecules from the class of amines on the oxidized surface of transition metals is suggested. According to this model, the process involves the capture of protons or hydroxyl groups forming on the oxide surface upon water molecule adsorption. The adequacy of the model is demonstrated experimentally with test amines, such as Novocaine (procaine), bencaine, Dimedrol (diphenylhydramine), etc. A theory of drift motion of ion beams that includes the space charge effect is proposed. It is shown that the quantity P _i=μj/ε₀ v _g ² (where μ is the ion mobility, j is the ion current density, ɛ₀ is the permittivity, and v _g is the longitudinal velocity of an ionized gas) plays the role of perveance for intense drift ion beams. A new type of drift-tube spectrometer that uses an ion source due to surface ionization is developed.     

Dispersive Fourier-transform spectroscopy of surface plasmons in the infrared frequency range

The optical scheme and the principle of operation of an asymmetric Mach-Zehnder interferometer for dispersive spectroscopy of surface IR plasmons are discussed. A thin-layer sample deposited on a conducting substrate, which guides surface plasmons, is placed in one of the arms of the interferometer. This makes it possible, by applying a complete Fourier transform to the interferogram, to obtain the spectrum of the complex refractive index of surface plasmons and, therefore, of the complex dielectric permittivity of the sample or the substrate material.     

表面等离激元与磁表面等离激元

金属微纳结构体系中的表面等离激元以及磁表面等离激元因其独特的光学特性吸引了研究者们的极大兴趣,成为当前的热点研究领域之一.文章对表面等离激元尤其是磁表面等离激元的特点、基本现象、新颖效应及其应用研究前景的最新发展进行了介绍.     

Channelling surface plasmons

Channel plasmon polaritons (CPPs) propagating along the bottom of subwavelength grooves cut into a metal surface were recently shown to exhibit strong confinement combined with low propagation loss, a feature that makes this guiding configuration very promising for the realisation of ultracompact photonic components. Here, the results of our investigations of CPP guiding by V-grooves cut into gold are presented, demonstrating efficient large-angle bending and splitting of radiation as well as waveguide-ring resonators and Bragg grating filters. Additionally, we present a simple model based on the effective-index method that accounts for the main features of CPP guiding, thus, providing a clear physical picture of this phenomenon. PACS 73.20.Mf; 71.36.+c; 42.82.-m; 07.79.Fc     

局域表面等离激元

局域表面等离激元使得贵金属纳米颗粒具有丰富的光学性质,其应用涵盖能源、生物医学、安全、信息、超材料等诸多领域。文章简要介绍局域表面等离激元的基本性质、贵金属纳米结构中的局域表面等离激元共振耦合以及具有局域表面等离激元特性的贵金属纳米结构的一些重要应用。     

Resonant surface plasmons of a metal nanosphere treated as propagating surface plasmons

On the assumption that the resonant surface plasmons on a spherical nanoparticle are formed by standing waves of two counter-propagating surface plasmon waves along the surface, by using Mie theory simulation, we find that the dispersions of surface plasmon resonant modes supported by silver nanospheres match with those of the surface plasmons on a semiinfinite medium-silver interface very well. This suggests that the resonant surface plasmons of a metal nanosphere can be treated as a propagating surface plasmon wave.     

Understanding fractional-order surface plasmons

We show experimentally that diffraction-induced surface plasmon excitation can mimic enhanced transmission and cause a highly sensitive modulation by the coherent interference between zero-order and reflected first-order diffraction in select regions of the terahertz spectrum. Based on the study of a one-dimensional metallic grating, we obtain the physical mechanisms of the fractional-order surface plasmon resonances observed with the two-dimensional grating of the metallic hole array.     

Electrical excitation of surface plasmons

We exploit a plasmon mediated two-step momentum down-conversion scheme to convert low-energy tunneling electrons into propagating photons. Surface plasmon polaritons (SPPs) propagating along an extended gold nanowire are excited on one end by low-energy electron tunneling and are then converted to free-propagating photons at the other end. The separation of excitation and outcoupling proves that tunneling electrons excite gap plasmons that subsequently couple to propagating plasmons. Our work shows that electron tunneling provides a nonoptical, voltage-controlled, and low-energy pathway for launching SPPs in nanostructures, such as plasmonic waveguides.     

The surface relaxation of Al as determined by electron energy loss spectroscopy on plasmons

Electron energy loss spectroscopy (EELS) on plasmons has been applied to determine the thermal expansion coefficient on the surface and to estimate the density of conduction electrons in the surface layer of aluminium. Using the data on the temperature dependence of the surface plasmon energy shift, the value of thermal expansion coefficient on the surface was calculated to be α_s=1.3 × 10^?4K^?1 that is about two times higher than the bulk value. A simple model is proposed which takes account of the influence of electron density non-uniformity in the surface layer on the dispersion of plasma oscillations. An estimation of the density of conduction electrons in the surface layer based on the observed dependence of the surface plasmon energy on the energy of primary electrons gave a value about 5% lower than the bulk value. The thickness of altered surface layer is about 10 Å.     

Ultrafast control of grating-assisted light coupling to surface plasmons

We demonstrate subpicosecond control over the coupling of free-space radiation to surface-plasmon polaritons using 830 and 500 nm period gold gratings. Thermal changes to the electron distribution following irradiation by 100 fs, 810 nm pulses produce a shift of the 570 nm plasmon resonance by ~0.75 nm with reflectivity change up to 6% and decay time of ~1 ps.     

Electrooptic reflection with surface plasmons

Electrooptic reflection with surface plasmons is studied both experimentally and theoretically. An attenuated total reflection (ATR) geometry is used in which a quartz electrooptic crystal onto which a thin Ag film has been evaporated is contacted to the hypotenuse face of a high-index prism. Modulation in the ATR of an He–Ne beam near the angle for surface plasmon excitation is observed when a low-frequency electric field is applied to the quartz crystal. Experiments have been done with both single and multiple boundary surface waves. The angular spectra show phase reversal structure due to the interference of the modulated reflected wave with the ATR wave. The modulated reflectance is calculated directly from a well-known solution to the boundary value problem in nonlinear optics. Good quantitative agreement with the observations is obtained.     

Physical adsorption and surface plasmons

The quantum mechanical formulation of the screening of a point charge by surface plasmons is extended to describe the coupling of a fluctuating atomic dipole with a metallic surface of planar, spherical or cylindrical shape. This allows for the calculation of the nonretarded Van der Waals attraction of an atom by a solid surface in the three different geometries. Applications of the theoretical formulae are made to obtain numerical values of the dispersion energy by a spherical particle, a spherical pore, a thin film, a slot-like prore, a cylindrical fiber or a cylindrical pore.     

Quantum optics with surface plasmons

We describe a technique that enables strong, coherent coupling between individual optical emitters and guided plasmon excitations in conducting nanostructures at optical frequencies. We show that under realistic conditions optical emission can be almost entirely directed into the plasmon modes. As an example, we describe an application of this technique involving efficient generation of single photons on demand, in which the plasmon is efficiently outcoupled to a dielectric waveguide.     

A note on surface plasmons

We consider the dispersion of the surface plasmons in an approximate RPA. It is shown that the usual linear dependence of the frequency on the wave vector is valid in the high density limit.     

Four-step pulses of fractional-order surface plasmons

The 0-order transmission of a 1D metallic grating, on a high-resistivity silicon wafer in optical contact with a silicon plate, has been characterized by terahertz time-domain spectroscopy with subpicosecond resolution over a 400 ps scan range. Two new long-time-delay, powerful pulses are observed after the second reflected pulse. In the frequency domain, these two strong and fast-ringing structures correspond to the bandwidth ranges between the [0, 1] and [0, 2] surface plasmon modes and the range above [0, 2], respectively. A physical optics ray analysis provides an intuitive understanding of these new four-step (reflection, diffraction, total reflection, and diffraction) pulses, caused by fractional-order surface plasmon type beam coupling.     

Generating maximum entanglement under asymmetric couplings to surface plasmons

Generating entangled states is a vital ingredient for quantum information engineering. Here, we investigate the entanglement generation between two quantum dots coupled to nanoring surface plasmons with asymmetric coupling strength g(1) and g(2). The dynamics of concurrence C is obtained by solving the corresponding master equation. High entanglement can be generated at appropriate times through the scatterings of the incident field and its scattered field. Furthermore, we find that maximum entanglement can be created when r≡g(1)/g(2) is the ratio of odd numbers. Contrary to intuition, relative high entanglement (C?1) can remain even if the ratio r is far off the required values, which is useful in real experiments.     

Dispersion of surface plasmons in InSb-gratings

The reflection of a monochromatic plane electromagnetic wave by a grating consisting of grooves in the surface of a semiconductor plasma (InSb) is investigated theoretically, in particular in that region of frequencies where the complex permittivity of the semiconductor plasma has a negative real part. From the numerically obtained reflection factor pertaining to anH-polarized incident wave, the excitation and the dispersion of surface plasmons at the boundary of the medium is discussed. The grating problem is rigorously formulated as a boundary value problem employing a Green's function technique. Numerical results pertaining to the reflection factor are presented for different grating parameters.