Optical properties of two-dimensional periodic systems of the dielectric micro bars and micro cones are investigated. Computer simulations as well as real experiment reveal anomalous optical response of the dielectric metasurface due to excitation of the dielectric and metal-dielectric resonances, which are excited in-between metal nanoparticles and dielectric cones and bars. In the metal-dielectric resonance local electric field can be orders on magnitude larger than the field in the plasmon resonance only. To investigate local electric field the signal molecules were deposited on the metal nanoparticles. We demonstrate the enhancement of the electro- magnetic field by detecting the Raman signal from the of organic acid molecules deposited on the investigated metasurface.
The main achievement of the modern plasmonics is the concentration of light into nanospots that are much smaller than the wavelength. Nanospot concentration is beneficial for various applications: biomedical imaging and sensing, optical microscopy with single-molecule resolution, heat assisted magnetic recording (HAMR), QED studies, nanolasing, etc. Until now, plasmonic metal nanoantennae, sub-wavelength apertures or metallic near field concentrators (NFCs) are used for this purpose. The main advantage of the metal NFC is their capabilities to localize plasmonic modes, which can be excited by the incident transverse em wave. However, the metal NFCs have large optic loss so we propose a novel all-dielectric NFC, which allows focusing the light into a sub-wavelength hot nanospot, without the dissipative loss. The detrimental dephasing and thermal effects almost vanishes in the dielectric NFC opening new opportunities in the magnetic recording and quantum plasmonics. The ability to concentrate light is important not only to fundamental physics studies, but also to practical device applications. For example, microcavities can force the atoms or quantum dots to emit spontaneous photons in a desired direction or can provide an environment, where dissipative mechanisms such as spontaneous emission are overcome. The electric field is much enhanced in the proposed new device at the vertex of the dielectric beak, which is attached to the tablet dielectric resonator. The resonator in turn is pumped through the plane waveguide. The electric field is enhanced due to longitudinal polarization of the beak vertex, which is excited by em field of the pumped resonator.
Plasmon nanolasers, also known as SPASERs, were suggested by Bergman and Stockman in 2003. Quantum plasmonics attract much attention in recent years due to the numerous potential applications in the plasmonics. We consider thermal effects in the metal nanoresonator immersed in the active, laser medium. The size of the resonator is much less than the wavelength. The plasmon field inside the nanoresonator operates as a quantum object. Due to the nanosize of the resonator, the internal plasmon electric field is about the atomic field even for few plasmon quants. The coupling between the plasmon field and plasmon resonator is anomalous strong. We develop the quantum dynamics of the plasmon field and show that the SPASER may be the subject of thermal instability. The loss in SPASER increases with increasing the temperature when the average number of the plasmons is maintained at the stationary level. Therefore, the heat generation increases with increasing the temperature. This positive feedback results in the thermal instability. When the energy, accumulated in the plasmon nanoresonator, exceeds the instability threshold the temperature increases exponentially. We find the increment of the temperature growth and lifetime as function of the loss in metal and the structure of the plasmon resonator. We consider how the thermal instability influences the luminescence and find how the lasing threshold is changed. The coherence of the light emitted by the plasmon laser is also considered. The thermal stability of the nanolaser is crucial for any practical application.
Concentration of light into nanospots is greatly beneficial for heat assisted magnetic recording, biomedical imag- ing and sensing, nanolasing, etc. We propose novel, all dielectric near field transducers, which allow focusing light into a hot spot, much smaller than the wavelength without significant dissipative loss. Therefore, the detri- mental thermal effects in heat assisted recording can be significantly reduced opening new venue in the magnetic recording. In the proposed transducer electric field concentrates at the apex of the dielectric tip attached to the resonator. Thus the electric field excited in the dielectric resonator is further amplified and concentrated due to the dipole polarization of the tip.
New dielectric metamaterial based on the Bragg filter comprising ten dielectric bilayers was investigated. Each bilayer is the thin films of silicone dioxide (SiO2) and another film of zirconium dioxide (ZrO2). The surface of the multilayer film is profiled. It has a form of periodic system of rectangles separated by the open gaps. We use the computer simulation as well as analytical solution to find the reflectance of the multilayer as a function of the wavelength and electromagnetic (em) field distribution. The multilayer system reveals the enhancement of em fields at the surface. The considered Bragg filter was modified by Raman-active structure made of gold nanoparticles with chemically attached 3,3-thio-bis(6- nitrobenzoic acid) - (TNB). The high Surface Enhanced Raman Scattering (SERS) signal was detected.
The quantum-mechanical and thermal phenomena in the plasmonic nanoparticle and resonator are investigated. We develop quantum plasmonics by quantizing the collective electron motion in the surface plasmon. The operator of the electric field inside the metal nanoparticle is found. Thus obtained quantum electric field is anomalous large even for few plasmon quanta. The strong electric field, which value is comparable with the atomic field, results in huge electric current and overheating the metal nanoparticle when it operates as a resonator for the plasmon laser (SPASER). It is shown the overheating thermal instability can explode the particle.
We propose multiple resonances in the thin profiled dielectric films. The excitation of the dielectric resonances results in giant electric and magnetic field fluctuations. We observe dielectric enhanced Raman scattering in the investigated dielectric films.
The surface plasmon (SP) excitations in the periodical array of the nanorods have attracted a lot of attention in the recent
years due to the numerous potential applications in nanoplasmonics including transmitting and processing optical signals
on a scale much smaller than the wavelength. In our work the plasmonic and dielectric systems consisting of twodimensional
periodic arrays of nanorods are considered. We use computer simulation as well as exact analytical solution
to find reflectance and transmittance the plane array of the nanorods, which have various diameters and inter-particle
spacing. As the metal nanorods approach each other, series of surface plasmon resonances are excited. The resonances
are strongly localized between nanorods due to its collective nature. It is shown that the local electric field is much
enhanced in the interparticle gap and it concentrates at a scale much smaller than the diameter of the rod. The reflectance
and transmittance have sharp minima and maxima corresponding to the excitation of various SP resonances. The
computer simulations are in an agreement with our analytical theory. In the case of the dielectric nanorods the
phenomenon of the whispering gallery modes effect is considered. The resonance frequencies and field enhancement can
be tuned by variation of the shape and arrangement of the nanorods. The system of nanorods that almost touched each
other by their generatrices can be used to develop plasmon and dielectric substrates, which are the basic elements of high
sensitive SERS bio and chemical sensors.
Quantum-mechanical theory of the plasmon nanoresonator laser is presented. The Hamiltonian equations of motion are obtained for the plasmon field in the time domain. Then the plasmon field is quantized to develop the quantum plasmonics (QP). QP equations are solved and dynamics of the plasmon laser is obtained. We show that the plasmon laser is essentially thresholdless device in the nanosize limit, which radiation is coherent regardless of the pumping rate. We obtain the statistics of quanta, intensity, spectrum and linewidth of the radiation. Theory can also be applied to the usual photonic microlasers, metal-dielectric lasers and other small cavity devices.
The surface plasmons (SPs) eigenproblem which arises in inhomogeneous metal-dielectric films is studied at resonance conditions. We show that short-range correlations present in the governing Kirchhoff Hamiltonian (KH) result in delocalization of the eigenstates at the center of the spectrum. The delocalization is manifested as a power law/logarithmic singularity for the density of states and SPs localization lengths. Based on the SPs eigenproblem, analytical relationships are derived for the electromagnetic response of the semicontinuous film in resonance and off-resonance regimes. Experimental studies indirectly confirm the existence of delocalized SP states in the random system.
We consider plasmonic nanoantennas immersed in active host medium. Specifically shaped metal nanoantennas can
exhibit strong magnetic properties in the optical spectral range due to the excitation of Magnetic Resonance Plasmons
(MRP). A case when a metamaterial comprising such nanoantennas can demonstrate both "left-handiness" and negative
permeability in the optical range is considered. We show that high losses predicted for optical "left-handed" materials
can be compensated in the gain medium. Gains required to achieve local generation in such magnetic active
metamaterials are calculated for real metals
Anderson localization in random potential fields has been studied extensively for the last fifty years. It is commonly accepted that in 1D and 2D systems characterized by non-correlated random potential distributions, all states are exponentially localized. In this paper we investigate the eigen-problem for Surface Plasmons (SP) in random metal-dielectric films. We show that short-range correlations presented in the governing Kirchhoff's Hamiltonian (KH) result in delocalization of the eigenstates at the band center. The delocalization is shown to be manifested through power law singularities for the density of states and SP localization lengths. The study of the system size dependence of the nearest neighbor's level spacing distributions shows a gradual shift of the SP eigen-problem from a metallic phase for small system sizes into an insulating quantum phase for infinite systems. It reveals a genuine metal-insulator transition that takes place in the composite and is characterized by quantum percolation threshold Pq which is higher than the corresponding geometrical critical concentration Pc.
It is predicted that metal nanostructures can have a magnetic plasmon resonance (MPR) in the optical spectral range. Similarly to the known electrical surface plasmon resonance (SPR), the MPR depends only on metal properties and geometry of the system, rather than on the wavelength, and it can occur in structures much smaller in size than the optical wavelength. The MPR can have as large optical cross-section as the SPR so that nanostructures supporting the two resonances can provide a strong coupling to both field components of light, electrical and magnetic. Above the resonance, the magnetic plasmon polarizability may acquire negative values making possible to use this phenomena for developing left-handed materials in the optic range.
High SERS sensitivity for protein detection has been accomplished with semicontinuous silver films. Specifically, an insulin surface density as low as 80 fmol/mm2 and 25 amol in a probed area has been readily detected.
Optical properties of metal nanowires and nanowire composite materials are studied experimentally and theoretically. We suggest that a nanowire composite, constructed from parallel pairs of nanowires has both effective magnetic permeability and dielectric permittivity negative in the visible and near-infrared spectral ranges due to resonant excitation of surface plasmon polaritons.
Experimental results confirm excitation of surface plasmons polaritons in periodical array of nanowires.
It has been known for some time (Rothman, 1962) that
meta-materials consisting of a network of metal wires share a number of electromagnetic properties with plasma. For example, both have a cutoff frequency at the effective plasma frequency of the mesh below which there is no wave propagation. These ideas have recently been re-discovered (Pendry, 1996) and applied to designing electromagnetic structures that have negative dielectric permittivity and magnetic permeability. The extent to which the electromagnetic properties of wire arrays actually mimics the properties of the plasma is still open to debate. We demonstrate that two-dimensional wire arrays are essentially different from plasmas in all aspects except having a cut-off for a particular wave polarization. On the other hand, three-dimensional wire arrays support the same classes of waves as the plasma: longitudinally polarized plasmons and transversely polarized photons. Electromagnetic properties of two and three-dimensional wire arrays are also expained using equivalent lumped circuits.
Analytical theory and numerical calculations for periodic arrays of metal nanoparticles indicate resonant-like enhancement of local electromagnetic field, which can be tuned by varying a ratio of particle diameter to interparticle spacing. For Raman scattering, local field enhancements on the order of 1013 and surface-averaged field enhancements on the order of 1011 can be achieved udner optimal conditions. This is several orders of magnitude greater tan that obtaiend in disordered metal-dielectric films, and suggests a new design for engineering plasmonic substrates supporting intense and spatially well-defined field patterns, with direct applications for surface-enhanced Raman scattering (SERS), and surface-enhanced optical nonlinearities.
An analytical theory for extraordinary light transmittance through an optically thick metal film with sub-wavelength holes is developed. It is shown that the film transmittance has sharp peaks that are due to the Maxwell-Garnet resonances in the holes. At resonances electric and magnetic fields are dramatically enhanced in the holes. These resonances are proposed to guide light over a metal film at a nanoscale.
We show that plamonic nanomaterials allow the localization and guiding light, with high efficiency, and molecule sensing, with unsurpassed sensitivity. Two types of palsmonic naomaterials are considered: metal nanowires and fractal colloid aggregates. The electromagnetic field distribution for thin metal nanowires is found, by using the discrete dipole approximation. The plasmon polariton modes in wires are numerically simulated. These modes are found to be dependent on the incident light wavelength and direction of propagation. The existence of localized plasmon modes and strong local field enhancement in percolation nanowire composites is demonstrated. Novel left-handed materials in the near-infrared and visible are proposed based on nanowire composites. Dramatic enhancement in fractal colloid aggregates and, especially, in fractal-microcavity composites are discussed along with new potential applications of these plasmonic materials.
Optical response of metal-dielectric inhomogeneous films is considered. The generalized Ohm's law is formulated that relates electric and magnetic fields outside to the currents inside the film. Computer simulations, with the use of the generalized Ohm's law show that the local electric and magnetic fields experience giant spatial fluctuations. The fields are localized in small spatially separated peaks: electric and magnetic hot spots. In these hot spots the local fields (both electric and magnetic) exceed the applied field by several orders of magnitude. It is also shown that transmittance of a regular modulated metal film is strongly enhanced when the incident wave is in resonance with surface polaritons in the film. A new optical switch based on this effect is proposed.
Patrice Gadenne, Bruno Berini, Stephanie Buil, Xavier Quelin, C. Anceau, S. Gresillon, S. Ducourtieux, Jean-Claude Rivoal, M. Breit, Alain Bourdon, Andrey Sarychev, Vladimir Shalaev
KEYWORDS: Polarization, Plasmons, Metals, Electromagnetism, Near field scanning optical microscopy, Gold, Thin films, Fractal analysis, Near field optics, Harmonic generation
It is now known that plasmon oscillations supported by nanostructured metal thin films of fractal morphology, can result in large local fields and strong enhancement of optical phenomena, for example Raman scattering. The localized plasmons, acting like nano-antennas, can concentrate very large electromagnetic energy in nanometer- sized areas, hot spots, and provide particularly strong enhancement of optical responses, in a very broad spectral range. Our new experimental results show up position dependence of the hot spots on the polarization state of the light. Moreover as expected from recent theoretical predictions, on this kind of thin percolating films, there is a dramatic enhancement of the second harmonic generation (2(omega) ) out of the specular directions. This unusual diffuse SHG could be connected to possible chirality of the percolating metallic films, which is expected to manifest itself as change in the hot-spot distribution for the left and right circularly polarized incident light.
A theory of optical, infrared, and microwave response of metal- dielectric inhomogeneous films is developed. The generalized Ohm's law is formulated. In this approach electric and magnetic fields outside a film can be related to the currents inside the film. Our computer simulations, show that the local electric and magnetic fields experience giant spatial fluctuations. The fields are localized in small spatially separated peaks: electric and magnetic hot spots. In these hot spots the local fields (both electric and magnetic) exceed the applied field by several orders of magnitude. The high-order field moments that characterize the average enhancement of Raman scattering and nonlinear optical processes are very large and frequency independent in a wide spectral range.
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