Visible frequency magnetic activity in silver nanocluster metamaterial

Influence of self- and cross-phase modulations on an optical frequency doubling process for metamaterials

In the process of doubling the frequency of high-power laser radiation in metamaterials, the self- and cross-phase modulations associated with the cubic nonlinearity of the medium are studied in the constant-intensity approximation. It is assumed that the pump wave propagates in a region with negative refraction. It is shown that in the case of a nonlinear-optical process of frequency doubling of an intense light wave in a metamaterial, it is important to take into account the self-action and cross-interaction effects that directly affect the optimal phase relationship between the interacting waves. It is discovered that, as a result of counter interaction of waves, the period of spatial beats changes. According to the analytic expressions obtained in the work, the choice of optimal parameters of the problem makes it possible to realize the regime of effective frequency doubling. By varying the intensity of the pump, it is possible to control and manipulate the intensity of the output coherent radiation from the minimum to the maximum value. A numerical evaluation of the efficiency of the doubling process in a metamaterial is given, and a comparison is made with similar results in LiNbO₃ and KDP crystals. It is demonstrated that the effects of self- and cross-modulation in media with negative refraction can be used as a powerful tool for developing effective frequency doublers in such materials.

Imaging Nanoscale Electromagnetic Near-Field Distributions Using Optical Forces

We demonstrate the application of Atomic Force Microscopy (AFM) for mapping optical near-fields with nanometer resolution, limited only by the AFM probe geometry. By detecting the optical force between a gold coated AFM probe and its image dipole on a glass substrate, we profile the electric field distributions of tightly focused laser beams with different polarizations. The experimentally recorded focal force maps agree well with theoretical predictions based on a dipole-dipole interaction model. We experimentally estimate the aspect ratio of the apex of gold coated AFM probe using only optical forces. We also show that the optical force between a sharp gold coated AFM probe and a spherical gold nanoparticle of radius 15 nm, is indicative of the electric field distribution between the two interacting particles. Photo Induced Force Microscopy (PIFM) allows for background free, thermal noise limited mechanical imaging of optical phenomenon over wide range of wavelengths from Visible to RF with detection sensitivity limited only by AFM performance.

Review of Plasmonic Nanocomposite Metamaterial Absorber

Plasmonic metamaterials are artificial materials typically composed of noble metals in which the features of photonics and electronics are linked by coupling photons to conduction electrons of metal (known as surface plasmon). These rationally designed structures have spurred interest noticeably since they demonstrate some fascinating properties which are unattainable with naturally occurring materials. Complete absorption of light is one of the recent exotic properties of plasmonic metamaterials which has broadened its application area considerably. This is realized by designing a medium whose impedance matches that of free space while being opaque. If such a medium is filled with some lossy medium, the resulting structure can absorb light totally in a sharp or broad frequency range. Although several types of metamaterials perfect absorber have been demonstrated so far, in the current paper we overview (and focus on) perfect absorbers based on nanocomposites where the total thickness is a few tens of nanometer and the absorption band is broad, tunable and insensitive to the angle of incidence. The nanocomposites consist of metal nanoparticles embedded in a dielectric matrix with a high filling factor close to the percolation threshold. The filling factor can be tailored by the vapor phase co-deposition of the metallic and dielectric components. In addition, novel wet chemical approaches are discussed which are bio-inspired or involve synthesis within levitating Leidenfrost drops, for instance. Moreover, theoretical considerations, optical properties, and potential application of perfect absorbers will be presented.

Plasmonic mode engineering with templated self-assembled nanoclusters

Plasmonic nanoparticle assemblies are a materials platform in which optical modes, resonant frequencies, and near-field intensities can be specified by the number and position of nanoparticles in a cluster. A current challenge is to achieve clusters with higher yields and new types of shapes. In this Letter, we show that a broad range of plasmonic nanoshell nanoclusters can be assembled onto a lithographically defined elastomeric substrate with relatively high yields using templated assembly. We assemble and measure the optical properties of three cluster types: Fano-resonant heptamers, linear chains, and rings of nanoparticles. The yield of heptamer clusters is measured to be over 30%. The assembly of plasmonic nanoclusters on an elastomer paves the way for new classes of plasmonic nanocircuits and colloidal metamaterials that can be transfer-printed onto various substrate media.

Optical properties of a fabricated self-assembled bottom-up bulk metamaterial

We investigate the optical properties of a true three-dimensional metamaterial that was fabricated using a self-assembly bottom-up technology. The metamaterial consists of closely packed spherical clusters being formed by a large number of non-touching gold nanoparticles. After presenting experimental results, we apply a generalized Mie theory to analyze its spectral response revealing that it is dominated by a magnetic dipole contribution. By using an effective medium theory we show that the fabricated metamaterial exhibits a dispersive effective permeability, i.e. artificial magnetism. Although this metamaterial is not yet left-handed it might serve as a starting point for achieving bulk metamaterials by using bottom-up approaches.

Assembly, structure and optical response of three-dimensional dynamically tunable multicomponent superlattices

We report the successful fabrication of optically active three-dimensional (3D) superlattices that incorporate DNA-encoded components, metallic nanoparticles, and molecular chromophores in well-defined positions. A DNA linker with three distinct binding sites serves as an assembly agent and dynamically tunable structural element for the superlattice. Using small angle X-ray scattering we have revealed the organization of particle-chromophore 3D arrays and monitored their reversible contractions and expansions that were modulated by ionic strength changes. As the distance between the molecular chromophores and plasmonic nanoparticles in the superlattice was regulated in situ, we were able to uncover the relationship between experimentally determined structure and optical response of the system. This dynamical tunability of superlattice results in a dramatic optical response: nearly a three times change of emission rate of the chromophore. The evolution of lifetime with structural changes reasonably agrees with the calculations based on a cumulitative coupling of chromophores with metallic nanoparticles in different coordination shells.