Lighting up multipolar surface plasmon polaritons by collective resonances in arrays of nanoantennas

We demonstrate the coupling of multipolar surface plasmons with photonic modes in periodic arrays of metallic nanoantennas. This coupling leads to sharp resonances known as lattice surface modes. In spite of the weak interaction of multipolar surface plasmons with light, lattice surface modes provide an efficient radiative decay channel for emitters in the proximity of the array. We observe a tenfold emission enhancement of dyes coupled to lattice resonances. Lattice surface modes light up multipolar plasmonic resonances, opening new possibilities for fluorescence spectroscopies.     

Efficient Integration of Single-Photon Emitters in Thin InSe Films into Resonance Silicon Waveguides

A concept of the optimal design of a silicon waveguide based on optically coupled Mie-resonant nanoantennas for efficient inputting of light from point emitters associated with excitons localized at defects in a thin InSe film is proposed. Numerical calculations demonstrate that the efficiency of coupling between a dipole emitter and a resonant silicon waveguide is four orders of magnitude greater than that for a conventional ridge waveguide.

     

Enhanced light extraction with silicon nanoantenna arrays for white light LED applications

High conversion efficiency and quantum efficiency is essential for the phosphor in an efficient phosphor-based white light LEDs. Here, based on the coherent harmonic and the random independent emitter model, we demonstrate theoretically that the silicon nanoantenna array can dramatically enhance the output power of emitters in a phosphor layer by investigating the far-field radiation enhancement of an electric dipole assisted by silicon nanopillars in a waveguide structure. Compared with the plasmonic silver nanoantenna array, the silicon nanoantenna array can increase the enhancement factor of light extraction efficiency (LEE) over 50% for the dipole source at the wavelength of 620 nm, thus showing potential applications in white light LEDs. The enhanced LEE is ascribed to the low-loss directional light scattering of silicon nanoantennas and the strong guided mode resonances caused by their array. The calculation results also indicate that the far-field radiation can be tailored significantly by changing the aspect ratio of silicon nanopillars while presenting a good directivity. Our research is expected to give more insights into the design and optimization of the solid-state lighting, gaining and lasing systems by integrating silicon-based nanoantennas.     

Calculation of intraband electronic and interband hole luminescence spectra of various alkali halide crystals under pulsed excitation by intense electron and laser beams in the nanosecond and picosecond regimes

We perform a theoretical analysis of the spectra of two rather new kinds of fundamental luminescence in dielectrics: intraband electronic and interband hole emissions. The primary photon emitters are radiative transition of ionization-passive conduction-band electrons and valence-band holes. These types of luminescence have been observed and studied experimentally by the use of two powerful nanosecond and picosecond radiation sources: strong electronic accelerators and lasers with ultraviolet harmonic generators. Good agreement is obtained between the calculated spectra and the ones measured experimentally. Comparison of the results with the experimental data makes it possible to determine certain important parameters of the electron spectrum, in particular the upper boundary of the passive region for ionization of the conduction band in crystalline CsI. Institute for Ultraprecise Electronics, Siberian Division, Russian Academy of Sciences. Polytekhnic University, Tomsk. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 103–115, December, 1995.     

Manipulating Light in Coupled Asymmetric Nanostructures Induced by a Visible–NIR Laser

We design an asymmetric nanostructure in the longitudinal direction at the visible–NIR range, which enables high enhancement factor and has the properties of Fano resonance induced by a visible–NIR laser. By simulating and analyzing the resonance frequency spectra of various nanorods, nanodipoles, and combined nanoantennas, we optimize the resonant spectra and enhanced factor of such nanoantennas. It has broad-band resonant spectra with a FWHM from 800 to 1,100 nm and possesses two resonant peaks at 870 and 1,000 nm, with an enhancement factor of 24. The current density distribution in such nanoantennas with different phases is also simulated in order to investigate its resonant mode. This theoretical study paves the way towards nanoscale lightwave control and spectral splitting. The designed nanodevices provide great potential for applications in ultrasensitive color sorters and biosensors induced by visible–NIR lasers.     

Broadband scattering by tapered nanoantennas

We realize a new design of tapered Yagi–Uda nanoantennas and experimentally study their far‐field light scattering. We show that in comparison with untapered structures the tapered nanoantennas exhibit broadband resonances featuring a distinct line shape. Our observations are supported by numerical calculations, which further reveal the tapered nanoantenna's wavelength‐dependent optical near‐field confinement. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

New Type of Quantum Emitters Related to Dislocations in Crystalline CdZnTe Revealed by Laser-Based Spectroscopy

Based on the measurements of spectra and polarization of low-temperature (5K) microphotoluminescence excited by stabilized continuous-wave laser pumping, we find a new type of isolated emitters formed due to the dislocations in crystalline CdZnTe. For an emitter of this type, zero-phonon luminescence is located 30–50 meV above the usual dislocation luminescence and is subjected to giant fluctuations of spectral position (~10 meV) and intensity. A noticeable degree of linear polarization in the plane containing <110> directions indicates the strongly anisotropic nature of the corresponding electronic states and confirms their connection with dislocations.     

Field emission from carbon nanotubes: perspectives for applications and clues to the emission mechanism

We report on the extensive characterization of carbon nanotube electron field emitters. We studied the emission behavior of single-wall, closed and opened arc-discharge multi-wall, and catalytically grown multi-wall nanotubes, as single emitters and in film form. The nanotube field emitters show excellent field emission properties, but significant differences were observed between the different types of nanotubes. To obtain good performances as well as long emitter lifetimes, the nanotubes should be multi-walled and have closed, well-ordered tips. Complementary results such as energy distribution and luminescence induced by the field emission give further precious indications on the field emission mechanism. The large field amplification factor, arising from the small radius of curvature of the nanotube tips, is partly responsible for the good emission characteristics. Additional evidence however shows that the density of states at the tip is non-metallic, appearing in the form of localized states with well-defined energy levels. Received: 15 May 1999 / Accepted: 18 May 1999 / Published online: 29 July 1999     

Fabry–Perot effect on dimer nanoantennas

In this work, we investigate the interaction between a single quantum emitter and dimer nanoantennas through a Fabry–Perot structure composed of an appropriate combination of two dielectric layers. This type of dielectric configuration is well known in the microwave region to increase the antenna performance, such as directivity, radiation efficiency, and radiation resistance. Here, the Fabry–Perot concept is transposed to the optical domain. The single emitter couples to the antenna through the dielectric structure, giving rise to a wide aperture field on top of the dielectrics with the same polarization of the emitter. This purely polarized aperture field can be used to excite one or more conveniently spaced nanoantennas. We demonstrate by 3D numerical calculations that the directivity and excitation rate of a single dimer is highly increased. Also, we show that multiple dimers arranged in an array configuration can be enhanced due to the wide aperture field generated by a single emitter.     

Compact and high-efficient wavelength demultiplexing coupler based on high-index dielectric nanoantennas

Wavelength demultiplexing waveguide couplers have important applications in integrated nanophotonic devices. Two of the most important indicators of the quality of a wavelength demultiplexing coupler are coupling efficiency and splitting ratio. In this study, we utilize two asymmetric high-index dielectric nanoantennas directly positioned on top of a silicon-on insulator waveguide to realize a compact wavelength demultiplexing coupler in a communication band, which is based on the interference of the waveguide modes coupled by the two nanoantennas. We add a Au substrate for further increasing the coupling efficiency. This has constructive and destructive influences on the antenna's in-coupling efficiency owing to the Fabry-Perot(FP) resonance in the SiO_2 layer. Therefore, we can realize a wavelength demultiplexing coupler with compact size and high coupling efficiency. This coupler has widespread applications in the areas of wavelength filters,on-chip signal processing, and integrated nanophotonic circuits.     

Optical spectroscopy of single impurity centers in semiconductors

Using optical spectroscopy with diffraction limited spatial resolution, the possibility of measuring the luminescence from single impurity centers in a semiconductor is demonstrated. Selectively studying individual centers that are formed by two neighboring nitrogen atoms in GaAs makes it possible to unveil their otherwise concealed polarization anisotropy, analyze their selection rules, identify their particular configuration, map their spatial distribution, and demonstrate the presence of a diversity of local environments. Circumventing the limitation imposed by ensemble averaging and the ability to discriminate the individual electronic responses from discrete emitters provides an unprecedented perspective on the nanoscience of impurities.     

Few-bubble luminescence in the acoustic field of a spherical resonator in aqueous solutions of sodium and terbium compounds

Stabilization and the luminescence mode during slight motion around the equilibrium position of a few (two to eight) bubbles in 2–6 mol/L aqueous solutions of NaCl, NaOH, TbCl saturated with argon were achieved in a device for monitoring single-bubble sonoluminescence in a spherical resonator. Examples are presented of this variety of multibubble sonoluminescence illustrating various spatial-spectral distributions of cavitation bubbles, which contain either emitters comprising only the solvent continuum or also metal emitters (Na*, Tb³⁺*). Stabilization of bubbles in the form of closely (0.5–1 mm) located pairs of bubbles is of particular interest, in one of which only the solvent luminesces, and in the other, a metal.     

Input impedance, nanocircuit loading, and radiation tuning of optical nanoantennas

Here we explore the radiation features of optical nanoantennas, analyzing the concepts of optical input impedance, optical radiation resistance, impedance matching, and loading of plasmonic nanodipoles. We discuss how the concept of antenna impedance may be applied to optical frequencies and how its quantity may be properly defined and evaluated. We exploit these concepts in the optimization of nanoantenna loading by optical nanocircuit elements, extending classic concepts of radio-frequency antenna theory to the visible regime for the proper design and matching of plasmonic nanoantennas.     

Germanium–vacancy color center in isotopically enriched diamonds synthesized at high pressures

We report on the high-pressure synthesis of novel nano- and microcrystalline diamonds with germanium–vacancy (Ge–V) color centers emitting at 602 nm. The synthesis was carried out in non-metallic growth systems C–H–Ge and C–H–O–Ge enriched with germanium and carbon isotopes. We demonstrate germanium and carbon isotope shifts in the fine structure of the luminescence, which allows us to unambiguously associate the center with the germanium impurity entering into the diamond lattice. We show that there are two ground-state energy levels with the separation of 0.7 meV and two excited-state levels separated by 4.6 meV in the electronic structure of the center and suggest a split-vacancy structure of this center. High-intensity and narrow-line emission of high-pressure synthesized small diamonds with Ge–V centers makes them promising candidates for single-photon emitters.     

Scattering of Circularly Polarized Terahertz Waves on a Graphene Nanoantenna

We present a surface current method to model the graphene rectangular nanoantenna scattering in the terahertz band with Comsol.Compared with the equivalent thin slab method,the results obtained by the surface current method are more accurate and efficient.Then the electromagnetic scattering of circularly polarized terahertz waves on graphene nanoantennas is numerically analyzed by utilizing the surface current method.The dependences of the antenna resonant frequency with the circularly polarized wave on width and length are consistent with those for the linear polarized waves.These results are proved to be useful to design efficient nanoantennas in terahertz wireless communications.     

Field enhancement of gold optical nanoantennas mounted on a dielectric waveguide

In this paper, we investigate the localized field enhancement of optical nanoantennas consisting of different types of coupled gold nanoparticles and fed by a silicon nitrite slab waveguide. The optical nanoantenna is mounted on the surface of the waveguide, and the incident blue-violet light is guided in the slab waveguide and then reflected to the nanoatenna at the end of the waveguide. We also study the performance of the slab waveguide with different optimized parameters and also the field enhancement achieved by different shapes of nanoantennas.     

Low Level Laser Therapy: laser radiation absorption in biological tissues

We theoretically show that a polarization-independent optical band-stop filter operation can be performed by a two-dimensional sub-wavelength array of symmetric cross-shaped plasmonic nanoantennas. The proposed filter’s optical properties can be controlled by varying the size and periodicity of the plasmonic nanoantennas. So, this can be used to design filters in many frequency ranges of interest. In addition, the filter is simply constructed as a coating with only 30-nm thickness, which is much thinner than the operation wavelength, and thus facilitates the fabrication and further large-scale optical integration.     

Threshold Effect in the Photoemission of Composite Nanoantennas Irradiated by Intense Femtosecond Laser Pulses

JETP Letters - A new mechanism has been proposed for the formation of energy spectra of photoelectrons by above-threshold photoemission of composite nanoantennas with small gaps between elements...     

Fabrication of electrically contacted plasmonic Schottky nanoantennas on silicon

We fabricate Schottky contact photodetectors based on electrically contacted Au nanoantennas on p-Si for the plasmonic detection of sub-bandgap photons in the optical communications wavelength range. Based on a physical model for the internal photoemission of hot carriers, photons coupled onto the Au nanoantennas excite resonant plasmons, which decay into energetic "hot" holes emitted over the Schottky barrier at the Au/p-Si interface, resulting in a photocurrent. In our device, the active Schottky area consists of Au/p-Si contact and is very small, whereas the probing pad for external electrical interconnection is larger but consists of Au/Ti/p-Si contact having a comparatively higher Schottky barrier, thus producing negligible photo and dark currents.We describe fabrication that involves an electron-beam lithography step overlaid with photolithography. This highly compact component is very promising for applications in high-density Si photonics.     

电致发光衰减测量系统的搭建及应用

发光衰减是发光的重要过程,测量发光寿命对研究发光机理十分重要,但传统研究在概念和方法上存在两个差错：(1)概念上认为衰减等同于激发态数目的减少,而忽视了衰减是发光强度的下降,两者是不同的概念;(2)方法上基于激发态规律推导,假设的边界条件不符合实际,没有实验的支持。同时,传统方法对设备的要求很高,且只限于光致发光。为了纠正差错,降低成本,搭建了一套全新的电致发光衰减测量系统,可用于所有可以周期激发的发光类型。从能量转换原理出发,采用周期激发,用脉冲间隔时间作为时间尺度来度量发光衰减持续的时间,通过脉冲间隔时间与发光寿命的对比,相应地发光强度有不同的变化,根据该现象简便地测量出发光寿命。基于该原理搭建的发光衰减测量系统,实验结果表明了发光强度随着激发频率,先保持不变然后逐渐下降,通过测量下折点即能够推算出发光衰减寿命,而且还发现发光衰减寿命与初始发光强度呈正相关的关系。认为发光寿命是发光强度的变化,是区别于传统研究以激发态数目为研究对象的一大创新,同时通过实验证明了发光寿命与初始亮度相关,也拓展了对发光寿命的新认识。