Nano-infrared imaging of localized plasmons in graphene nano-resonators

We conduct in-situ near-field imaging of propagating and localized plasmons(cavity and dipole modes) in graphene nano-resonator. Compared with propagating graphene plasmons, the localized modes show twofold near-field amplitude and high volume confining ability(~ 10~6). The cavity resonance and dipole mode of graphene plasmons can be effectively controlled through optical method. Furthermore, our numerical simulation shows quantitative agreement with experimental measurements. The results provide insights into the nature of localized graphene plasmons and demonstrate a new way to study the localization of polaritons in Van der Waals materials.     

Absorption and Scattering of Light by Hybrid Metal/J-Aggregate Nanoparticles: Plasmon–Exciton Coupling and Size Effects

We report the results of our theoretical studies of the optical properties of hybrid nanoparticles consisting of the metal core covered with molecular J-aggregates. We evaluate the cross sections of absorption and scattering of light by such particles on the basis of the extended Mie theory for two concentric spheres with material dielectric functions that take into account the size effect associated with scattering of free electrons from the core/shell interface. We carry out our calculations in a wide range of light wavelengths and geometrical parameters of the composite system for silver and gold core and for a J-aggregate shell composed of different cyanine dyes. The results obtained demonstrate the quite different behavior of the extinction spectra of such particles caused by the different strengths of interaction between the Frenkel exciton and the dipolar or multipolar plasmons. We pay particular attention to the investigation of spectral peak positions associated with the eigenfrequencies of hybrid modes in the system and peak intensities as functions of reduced oscillator strength in the molecular J-band for various relationships between the core radius and shell thickness. This provides an efficient means for the explanation of the main features in the optical properties of metal/J-aggregate nanoparticles and can be used for an effective control of the plasmon–exciton coupling strength in such hybrid complexes.     

石墨烯等离激元的光学性质及其应用前景

石墨烯等离激元由于其独特的电学可调性、本征低衰减以及局域光场高度增强等特性, 引起了广泛的关注并迅速成长为一门新的学科分支--石墨烯表面等离激元光子学. 本文介绍了石墨烯等离激元的一些基本性质, 包括色散关系、局域的等离激元和传导的等离激元以及石墨烯等离激元对其周边介电环境的敏感性等. 在此基础上, 进一步介绍了石墨烯等离激元在太赫兹到中红外频段的应用, 比如有源光调制器的一些功能器件和增强的红外光谱探测等.     

Localization of Plasmons in Finite Three-Tile Quasiperiodic superlattices

The plasmons in a finite array of coupled two-dimensional electron gases arranged in a threetile quasiperiodic sequence are studied. We calculate the dispersion relation and investigate the localization of the plasmons. For a given in-plane wavevector the discrete modes form a series of bands. Extended and localized modes may coexist in the three-tile quasiperiodic superlattices. The plasmons in low frequency bands are localized. Extended modes appear in the middle bands. Some Tamm-like surface modes are found.     

Surface plasmons at the interface between graphene and Kerr-type nonlinear media

The properties of surface plasmons localized at the interface between graphene and Kerr-type nonlinear substrates are investigated analytically. Although the relative propagation distance remains the same, the dispersion of graphene plasmons may be affected much by the inevitable nonlinear effect of substrates. Specifically, the wavelength of graphene plasmons can be tuned by adjusting the nonlinear permittivity of substrates.     

Selective excitation of multipolar surface plasmon in a graphene-coated dielectric particle by Laguerre Gaussian beam

Localized surface plasmonic resonance has attracted extensive attention since it allows for great enhancement of local field intensity on the nanoparticle surface. In this paper, we make a systematic study on the excitation of localized surface plasmons of a graphene coated dielectric particle. Theoretical results show that both the intensity and frequency of the plasmonic resonant peak can be tuned effectively through modifying the graphene layer. Furthermore, high order localized surface plasmons could be excited and tuned selectively by the Laguerre Gaussian beam, which is induced by the optical angular orbital momentum transfer through the mutual interaction between the particle and the helical wavefront.Moreover, the profiles of the multipolar localized surface plasmons are illustrated in detail. The study provides rich potential applications in the plasmonic devices and the wavefront engineering nano-optics.     

Subwavelength propagation and localization of light using surface plasmons: A brief perspective

Surface plasmons at the metal–dielectric interface have emerged as an important candidate to propagate and localize light at subwavelength scales. By tailoring the geometry and arrangement of metallic nanoarchitectures, propagating and localized surface plasmons can be obtained. In this brief perspective, we discuss: (1) how surface plasmon polaritons (SPPs) and localized surface plasmons (LSPs) can be optically excited in metallic nanoarchitectures by employing a variety of optical microscopy methods; (2) how SPPs and LSPs in plasmonic nanowires can be utilized for subwavelength polarization optics and single-molecule surface-enhanced Raman scattering (SERS) on a photonic chip; and (3) how individual plasmonic nanowire can be optically manipulated using optical trapping methods.     

Light scattering from anisotropic particles: propagation,localization, and nonlinearity

Plasmon resonances and extraordinary light scatterings of a nanoparticle with radial anisotropy are studied and summarized. The coupling between localized surface plasmons and far‐field quantities is discussed. It is found that the presence of radial anisotropy redistributes the localization of plasmons and also results in certain novel phenomena in the far zone, which provide the possibility of scattering control such as electromagnetic transparency, enhanced scattering cross section, etc. The nonlinear optical response is explored in order to yield deeper physical insight into the interaction between plasmons and incident light.     

Dynamical behaviour of transverse plasmons in pair plasmas

This paper analytically investigates the nonlinear behaviour of transverse plasmons in pair plasmas on the basis of the nonlinear governing equations obtained from Vlasov--Maxwell equations. It shows that high frequency transverse plasmons are modulationally unstable with respect to the uniform state of the pair plasma. Such an instability would cause wave field collapse into a localized region. During the collapse process, ponderomotive expulsion is greatly enhanced for the increase of wave field strength, leading to the formation of localized density cavitons which are significant for the future experimental research in the interaction between high frequency electromagnetic waves and pair plasmas.     

Estimation of the Integral Role of Intershell Correlations in Heavy Atoms

The problem of controlling the quantum dynamics of localized plasmons has been considered in the model of a four-particle spaser composed of metallic nanoparticles and semiconductor quantum dots. Conditions for the observation of stable steady-state regimes of the formation of surface plasmons in this model have been determined in the mean-field approximation. It has been shown that the presence of strong dipole–dipole interactions between metallic nanoparticles of the spaser system leads to a considerable change in the quantum statistics of plasmons generated on the nanoparticles.     

不同密度银纳米粒子对氧化锌基发光二极管发光的增强

采用分子束外延法制备不同密度的银纳米粒子(AgNPs)修饰的局域表面等离子体共振增强n-ZnO/iZnO/MgO/p-GaN异质结发光二极管(LEDs),并对其电学及光学性质进行表征。结果显示:LEDs中引入适当浓度的AgNPs有利于AgNPs局域表面等离子体激元与ZnO激子相耦合,可以显著提高器件的电致发光性能;随着AgNPs浓度的增加,LEDs发光增强倍数先增大后减小,分析认为这是AgNPs局域表面等离子体共振耦合增强过程和AgNPs的消光过程两者之间相互博弈而导致的结果。     

Plasmonic band gaps and trapped plasmons on nanostructured metal surfaces

Nanostructured metal surfaces comprised of periodically arranged spherical voids are grown by electrochemical deposition through a self-assembled template. Detailed measurements of the angle- and orientation-dependent reflectivity reveal the spectral dispersion, from which we identify the presence of both delocalized Bragg and localized Mie plasmons. These couple strongly producing bonding and antibonding mixed plasmons with anomalous dispersion properties. Appropriate plasmon engineering of the void morphology selects the plasmon spatial and spectral positions, allowing these plasmonic crystal films to be optimized for a wide range of sensing applications.     

Phonon-plasmon interaction in tunneling GaAs/AlAs superlattices

The phonon-plasmon interaction in tunneling GaAs _n /AlAs _m superlattices (m=5and 6≥n≥0.6 monolayers) was studied by Raman scattering spectroscopy. The interaction of optical phonons localized in GaAs and AlAs layers with quasi-three-dimensional plasmons strengthens as the thickness of GaAs quantum wells decreases and the electronic states in the superlattices become delocalized due to tunneling. It is assumed that the plasmons also interact with the TO-like phonon modes localized in quantum islands or in thin ruffled layers.     

Tunable hybrid surface waves supported by a graphene layer

We study electromagnetic waves localized near the surface of a semi-infinite dielectric medium covered by a graphene layer in the presence of a strong external magnetic field. We demonstrate that a novel type of hybrid TE-TM polarized surface plasmons can propagate along the graphene layer. We analyze the effect of the Hall conductivity on the polarization properties of these hybrid surface waves and suggest a possibility to tune the graphene plasmons by the external magnetic field.     

Metal enhanced photoluminescence of near-infrared CdTexSe1−x quantum dots

High-quality alloyed near-infrared CdTe_xSe_1?x quantum dots were synthesized by a modified organometallic method. The emission wavelength of the alloyed quantum dots were turned from visible to near-infrared range by changing the composition of the precursor. The photoluminescence intensity of the alloyed quantum dots was further enhanced by coupling through localized surface plasmons from Au nanoparticles. The alloyed CdTeSe quantum dots coupled with Au nanoparticles exhibited a 4 times photoluminescence enhancement than that of bare CdTeSe quantum dots by turning the localized surface plasmons resonant absorption of Au nanoparticles consistent to the excitation wavelength. This method will be beneficial for the potential applications in the biological imaging and detection.     

Localized-to-propagating surface plasmon transitions in gold nanoslit gratings

Plasmon polaritons in thin gold nanoslit gratings with a fixed period and a variable filling factor are studied using microspectroscopy measurements and finite-difference time-domain simulations. The regimes of surface plasmon polaritons, localized plasmons, and the mixed mode are identified.     

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由色散方程和流体方程推导得到了横等离激元和对等离子体相互作用的非线性控制方程,利用场论的方法构建非线性控制方程的拉格朗日密度函数并求得相互作用过程中守恒的等离激元数和总能量。通过标度变换发现横等离激元由于调制不稳定性将坍塌形成小尺度的局域结构。在坍塌过程中横等离激元产生的有质动力随场强的增强而增强。由于有质动力对粒子的排斥,对等离子体中将产生小尺度的密度空穴。     

Channel plasmon-polariton in a triangular groove on a metal surface

One-dimensional localized plasmons (channel polaritons) guided by a triangular groove on a metal substrate are investigated numerically by means of a finite-difference time-domain algorithm. Dispersion, existence conditions, and dissipation of these waves are analyzed. In particular, it is demonstrated that the localization of the predicted plasmons in acute grooves may be substantially stronger than what is allowed by the diffraction limit. As a result, the predicted waves may be significant for the development of new subwavelength waveguides and interconnectors for nano-optics and photonics.     

The observation of the localized surface plasmons and its coupling

The surface plasmons properties on gold film composed of inverted square pyramidal pits were investigated. The near‐field scanning optical microscopy image showed that the surface plasmons were mainly located in the cavity of the pits; this is consistent with the mapping image obtained using the Raman scattering intensity of Rhodamine 6G. The calculation results obtained by using the finite element method showed that the electric field mainly located in the pyramidal pits and the field distribution was not affected by the adjacent pits around it. Compared with the single pyramidal pit, the localized electric field intensity increased in the condition of the structure array because of the surface plasmons coupling effect. The surface‐enhanced Raman scattering spectra intensity decreased as the incident angle of the excited laser increased except that there are two peaks at around 5° and 17.5°, which can be attributed to the Bragg scattering of the surface plasmons. The reflectance spectra collected by a microscope at different magnifications were different. The intensity variation between surface‐enhanced Raman scattering spectra obtained using ×20 and ×50 objective illustrated that the adsorption peak in the reflectance spectra corresponded to the surface plasmons coupling effect. Copyright © 2011 John Wiley & Sons, Ltd.     

Kinetics study of ultrafast electron transfer from sensitized dyes to silver halide microcrystals

Spectral sensitization micromechanism of cyanine dyes J-aggregate adsorbed on the tabular and cubic AgBr microcrystals with different dye concentrations is studied by using picosecond time-resolved fluorescence spectroscopy, and the dependences of electron transfer and spectral efficiency sensitization on different conditions are analysed in detail. With the steady spectroscopy, the wavelengths of absorption and fluorescence of J-aggregate adsorbed on AgBr microcrystals are found to shift to red relative to dye monomer. The spectrum of fluorescence has a red shift relative to the absorption peak. With the time-resolved fluorescence spectroscopy, the fluorescence decay curves of cyanine dyes J-aggregate adsorbed on the tabular and cubic AgBr grains are found to be fitted well by a double-exponential decay function. The fitting curves consist of a fast and a slow component. Because of the large amplitude of the fast component, this fast decay should be attributable mainly to the electron transfer from J-aggregate of dye to a conduction band of AgBr.