Active Coated Nano Particle Research Articles

Subwavelength plasmonic nanoantenna as a Plasmonic Induced Polarization Rotator (PI-PR)

This article reports the finding of the plasmonic induced polarization rotation and propagation rotation when the plane EM wave radiates the adjacent active coated nano particle and large dielectric sphere at resonant frequency. The results investigate that the incident electromagnetic planewave excites the TM21 mode in the large size dielectric sphere at first, which affects the TM11 mode field from the coated nano particle. Consequently, when the combined active coated nano particle and large dielectric sphere are in resonant, the main E–field polarization direction becomes parallel to the propagation direction of the original planewave and main beam of the pattern becomes omnidirectional i.e. both rotates by 90°. Furthermore, the polarization and propagation rotation angle varies with different size of the dielectric sphere. Likewise, the structure of dielectric sphere clamped by two active nanoparticles is also showing plasmonic induced polarization and propagation rotation along with TM11 mode from each coated nano particle (CNP) having 180° phase difference. In addition to this, the induced polarization rotation was also verified by the Electric Hertzian Dipole (EHD). The integration of this simpler geometry with other optical devices has possible applications in polarization manipulation, nano-sensors and detectors on nanoscale.

Cylindrical and Spherical Active Coated Nanoparticles as Nanoantennas: Active Nanoparticles as Nanoantennas

In this article, we review the fundamental properties of several spherical and cylindrical, passive, and active coated nanoparticles (CNPs) with an emphasis on their potential for nanoantenna and nanoamplifier synthesis. For the spherical geometries, the nanoparticles are excited by an electric Hertzian dipole (EHD), which represents, e.g., a stimulated atom or molecule. The cyl indr ical nanoparticles are excited by a magnetic line source (MLS). In the active cases, gain is added to the core region of the particle. For simplicity, it is represented by a canonical, frequency-independent gain model. We demonstrate that specific CNPs can be designed to be resonant and well matched to their respective excitation sources. With active cores, these designs can lead to extremely large total radiated powers. For both configurations, insights into the effects of the nanoparticle material composition, source location, and orientation will be given on the basis of studying their near-field and power-flow density distributions, total radiated powers, and directivity properties.

Impact of strong localization of the incident power density on the nano-amplifier characteristics of active coated nano-particles

Resonant, active coated nano-particles (CNPs) have been advocated as effective nano-amplifiers and nano-lasers. When it is properly designed to be in its super-resonant state, an electrically small active CNP captures significantly more of the incident field energy than its physical size suggests is possible. The corresponding enhancement of its extinction cross section is correlated with the concentration of the local field energy into its gain region. This energy localization can be visualized with the behavior of the flow lines of the Poynting vector field in the neighborhood of the CNP. Strong expulsion of the optical power generated from the interaction of the captured incident field energy with the gain medium creates an intense scattered field. As the interactions between the scattered field and the exciting plane wave increase, optical vortices form in the neighborhood of the active CNP. Gain depletion eventually occurs when the increase in the effective gain sufficiently detunes the resonance. A simple model for the gain enhancement effects observed in active CNPs is proposed that relates the enhanced effective size of the CNP caused by the field localization to the required gain necessary to achieve its super-resonant state. A comparison of the metal-covered, gain core, active CNP studied previously to the experimentally realized gain-impregnated silica-covered metal “SPASER” suggests that the active CNP design would require significantly less gain while offering a much larger enhancement of the incident field. Proposed modifications of both geometries that augment the field localization suggest further reductions in the gain values needed to achieve significant amplification of the output signal.

Impact of the excitation source and plasmonic material on cylindrical active coated nano-particles.

Electromagnetic properties of cylindrical active coated nano-particles comprised of a silica nano-cylinder core layered with a plasmonic concentric nano-shell are investigated for potential nano-sensor applications. Particular attention is devoted to the near-field properties of these particles, as well as to their far-field radiation characteristics, in the presence of an electric or a magnetic line source. A constant frequency canonical gain model is used to account for the gain introduced in the dielectric part of the nano-particle, whereas three different plasmonic materials (silver, gold, and copper) are employed and compared for the nano-shell layers.

Active coated nanoparticles: impact of plasmonic material choice

The near- and far-field properties of a number of active coated spherical nanoparticles excited by an electric Hertzian dipole at optical frequencies are investigated. Their enhanced, as well as reduced, radiation effects are demonstrated and compared.

CNP optical metamaterials

Simulation results for optical metamaterials (MTMs) derived from active coated nano-particle (CNP) inclusions for operation in the visible range of the spectrum between 400nm and 700nm are presented. Several examples of optical MTMs designed with these inclusions are characterized, including two-dimensional (2D) CNP metafilms; three-dimensional (3D) periodic CNP arrays; and 3D random CNP distributions. The properties of these optical MTMs are explored using effective medium theories that are applicable to these inclusion configurations. The effective permittivities and refractive indexes of these optical MTMs are compared and contrasted to the scattering properties of their active CNP inclusions.

Investigating functionalized active coated nanoparticles for use in nano-sensing applications

In this paper we investigate the use of active coated nanoparticles (CNPs) for nano-sensing applications. Simulation results of the optical properties of an active CNP with a 24nm radius active silica core and 6nm thick plasmonic shell made of silver that has been functionalized by an additional spherical outer layer of varying thickness and refractive index are presented. In particular, the effects of the functional-layer thickness and refractive index on the super-resonant (SR) state of the active CNP are presented. It is shown that the wavelength and optical gain required to excite the SR state may provide both a spectral and a power signature usable for nano-scale sensing and that these signatures may be used to identify the dimensions and optical properties of the functional layer. These results are then applied to the case of a functional layer containing a solution of human hemoglobin. It is demonstrated that the concentration of hemoglobin may be remotely determined from these SR signatures.