Session S38: Focus Session: Negative Index Materials: Concepts to Applications I

Plasmolecular Electronics and Photonics

Metallic nanostructures have received considerable attention for their ability to manipulate light at the nanoscale. Near-field optical measurements and electromagnetic simulations are presented that highlight the limitations and capabilities of such structures to guide, concentrate, and modulate surface plasmon-polaritons (SPPs). Systematic studies on (passive) metallic stripe waveguides are presented that demonstrate that the propagation of electromagnetic energy is mediated by a discrete number of guided SPP modes as well as a continuum of radiation modes. Using a parametric study of the propagation length as a function of stripe width and multimode interference studies, we will also show modal cutoff in narrow stripes. We then continue to show how the unique properties of SPPs and optically or electrically active molecules can be exploited to open up a new area of research: plasmolecular electronics and photonics. Several devices will be discussed that are based on nanoscale metal-molecule-metal junctions with optically active molecules developed for non-linear optics applications, such as spiropyrans and azobenzenes. In these junctions one can control the flow of electrons based on plasmonic signals or control the flow of surface plasmons based on an electronic signals. The implication of these results on the design of future plasmonic components will be discussed, as well as the potential synergy with electronic and photonic device technologies.   

New approach to all-angle-negative-refraction in two-dimensional photonic crystals

We show that with appropriate surface grating, all-angle-negative-refraction is possible in other frequency windows that were not realized before in two-dimensional photonic crystals. Previous flat lens using photonic crystals requires u+v $<<$ d. Our approach can be used to design flat lens with u+v$>>$d, thus being able to image large and/or far away objects. Our results are confirmed by FDTD simulations.   

Molecular Scale Imaging with A Smooth Superlens

Recent theory suggested a novel approach of optical imaging with resolution far beyond the diffraction limit. This can be done simply by exciting quasi-static surface plasmons of a thin silver film, allowing the recovery of evanescent waves in the near field image. Resolution as high as 60 nanometers or 1/6 of wavelength has been achieved experimentally. This unique optical superlens will enable parallel imaging and nanofabrication in a single snapshot, a feat that are not yet available with other nanoscale imaging techniques such as atomic force microscope or scanning electron microscope. In this paper, we demonstrate that such image resolution can be further refined through the use a multilayer superlens. Applying the state-of-the-art nanoimprint technology and surfactant mediated growth of silver film, we show that a smooth superlens can be fabricated with thickness down to 15nm. With optimized design of multilayer superlens (working wavelength of 380 nm), our experimental and numerical results both indicate the feasibility of resolving features of 30nm and below. The development of potential low-loss and high resolution superlens opens the door to exciting applications in nanoscale optical metrology and nanomanufacturing.   

Direct Magnetic Resonances with Infrared Light from Plasmonic Single Closed Ring Resonators

We report here a spectroscopic study on plasmonic ring resonators at grazing angle incidence. With the magnetic component of the infrared light perpendicular to the ring plane (TM), we successfully observed a strong resonance signal at Mid- to Near-IR frequencies. Comparing to simulations, we identify that this signal is due to the resonance of the TM wave with the surface plasmon propagation of the metal rings. We provide a solution to measure direct magnetic resonance by using a grazing incidence objective on a FTIR microscope. We also demonstrate a method to realize magnetic resonance at optical frequencies by channeling the surface plasmon in a closed metallic ring.   

Strong Broadband Resonances Observed between 1 and 3 microns from Nanolithographically Fabricated Metallic Metamaterials

We report in this talk strong broadband absorption resonances mid- and near-infrared frequencies from our nanometer size metamaterial resonators. We report a systematic study of these resonances with different dimensions of the resonators and their spacing, combined with our theoretical simulations. We will present our experimentally measured reflection at different incidence angles, and transmission of those resonators with different feature sizes and different lattice spacings which control the coupling between neighboring units. We found distinctively strong and broadband resonance in the spectrum of the resonators. We will discuss how our results can be used to introduce strong electric and magnetic responses and could provide a route to broadband negative refraction.   

Isotropic optical negative index of refraction metamaterials composed of randomly arranged nanoparticles

We report a strategy for achieving fully isotropic negative refraction index in a homogenized composite medium (HCM) conceptualized using both Maxwell-Garnett's and Lewin's effective medium formulations. The HCM consists of two isotropic dielectric-magnetic media (DMM): one DMM (randomly distributed small gold nanoparticles in free space) provides only negative permittivity, and another DMM (spherical SiC particles) provides only negative permeability via the Mie resonance. We prove, in the framework of the effective medium approach, that the mixture of DMMs (with properly adjusted fill factors and sizes of Au and SiC particles) exhibits isotropic negative refraction index metamaterial (NIM) behavior with negative refraction index of in a broad frequency range of the optical part of the spectrum. This result stands for both random distribution of the spherical constituent SiC particles (or Maxwell-Garnett arrangement), and the regular simple-cubic lattice of the same particles (Lewin's arrangement). Due to the high 3D isotropy of both models, both the analytical and numerical solutions of the scattering problems were found to be close to each other, and NIM behavior has been demonstrated. The calculations were carried out accurately taking into account the losses due to both gold and SiC nanoparticles.   

Left-handed Metamaterials in actively pumped Host Medium and Plasmonic Nanolaser

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 the Magnetic Plasmon Resonance. 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'' metamaterials can be compensated in the gain medium. We have derived condition under which nanoantennas filled with highly efficient gain medium can demonstrate low absorption or even gain sufficient for lasing. The host medium should have initial gain greater than 10$^{3}$ cm$^{-1}$. We propose plasmonic nanolaser, where the metal nanoantenna operates like a resonator. The size of the proposed plasmonic laser is much smaller than the wavelength. Therefore, it can serve as a very compact source of EM radiation.   

Electromagnetic forces in photonic crystals and in metamaterials

We investigate numerically the electromagnetic forces induced by a beam of light incident on a thin slab of (i) a photonic crystal (dielectric or metallo-dielectric) and (ii) a metamaterial of negative dielectric properties (negative index n, or individually negative permittivity and/or permeability). For photonic crystals, light excitation of the Mie and/or plasmon resonances of the individual ``atoms'' results in strong forces between the crystal layers. The influence of the band gaps on the forces is also discussed. For metamaterials, the interface forces (on either side of the slab) display an interesting spectrum associated with negative dielectric properties. In both systems, resonant dielectric behavior leads to strong field enhancement, large field gradients, and, consequently, strong electromagnetic forces. We also look at the forces between two slabs of metamaterial, or between alternating slabs of metamaterial and photonic crystal. Our calculations invoke the transfer matrix and FDTD algorithms, and we believe should prove relevant in the manipulation of nanoscale objects by laser light.   

All-angle negative refraction and imaging by anisotropic media

We have theoretically studied the optical property of silver/SiO$_{2}$ multilayers, as well as silver nanowires in a SiO$_{2 }$matrix. Under the approximation of the effective media theory, both structures can be described as highly anisotropic uniaxial materials. When the diagonal elements in the electric permittivity tensor of the effective media are opposite in signs, the transverse magnetic (TM) incident light can experience all-angle negative refraction and focusing due to the hyperbolic equal frequency contour. Moreover, this effect can be extended to a broad frequency region by adjusting the filling ratio of metals and the orientation of the structure. Full-wave simulations completely confirm the analytical predictions of the all-angle negative refraction and imaging phenomena. In comparison with left-handed metamaterials and photonic crystals, our approach with artificial anisotropic media opens up a simpler way to manipulate light propagation in the optical region, which has potential applications in photonic devices.   

Tunability of Superconducting Split-Ring Resonators With dc And rf Magnetic Fields

Superconducting split-ring resonators (SRRs) have lower metallic losses at microwave frequencies than do normal metal SRRs. However, they are very susceptible to slight perturbations in the electromagnetic fields due to nearby wires, SRRs, or even a conducting surface. These perturbations cause shifts in the SRR resonant frequency and degrade the $Q$. Superconducting SRRs may also experience a slight frequency shift, and large suppression of the $Q$, due to variations of the power of the applied electromagnetic wave. Data is shown for a single superconducting SRR in an applied dc magnetic field, and for rf power variations. In the former case, hysteresis was observed in both the resonant frequency and the $Q$, while in the latter case there was no hysteresis, however a large suppression of the $Q$ was observed at high power. Magneto-optical imaging was used to observe locations of vortex entry into the superconducting film, and a laser scanning microscopy measurement was performed to determine the current density profile in the SRR. The results presented may be used to tune the resonant frequency (and permeability) of the SRR to a desired frequency. This work was supported by the NSF, NASU, and DFG.