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ABSTRACT: We have employed a parallelized 3D FDTD (finite-difference time-domain) solver to study the electromagnetic properties of
random, semicontinuous, metal films. The structural features of the simulated geometries are exact copies of the fabricated
films and are obtained from SEM images of the films themselves. The simulation results show good agreement with the experimentally
observed far-field spectra, allowing us to also study the nonlinear moments of the optical responses for these realistic nanostructures.
These results help to further our understanding of the details of the electromagnetic response of randomly structured metal
films. Our results can also be applied in the optimization of random metal nanostructures and in the design of surface-enhanced
spectroscopies and other plasmonic applications.
Applied Physics B 04/2012; 100(1):159-168. · 2.19 Impact Factor
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ABSTRACT: A material parameter extraction procedure for general BI metamaterials has been presented. The retrieved material parameters correspond to those of the homogeneous BI material slab of the same thickness that produces the same transmission and reflection properties. A doubly-periodic chiral NIM design in the near-IR spectrum has been presented along with the extracted material parameters.
Antennas and Propagation Society International Symposium, 2008. AP-S 2008. IEEE; 08/2008
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ABSTRACT: Plasmonic filters were fabricated based on gold fractal nanostructures grown on silica microspheres. The fractal nanostructures were modified using laser irradiation, resulting in decreased extinction in the mid-infrared range.
Lasers and Electro-Optics, 2008 and 2008 Conference on Quantum Electronics and Laser Science. CLEO/QELS 2008. Conference on; 06/2008
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ABSTRACT: A negative index metamaterial demonstrating n=¿1.0+0.8i with both negative effective permittivity and permeability at 813 nm of linearly polarized light is fabricated. It also exhibits a negative refractive index at 770 nm for orthogonal polarization.
Quantum Electronics and Laser Science Conference, 2007. QELS '07; 06/2007
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ABSTRACT: The compensation of loss in metal by gain in interfacing dielectric has been demonstrated in a mixture of aggregated silver
nanoparticles and rhodamine 6G dye. An increase of the quality factor of surface plasmon (SP) resonance was evidenced by the
sixfold enhancement of Rayleigh scattering. The compensation of plasmonic losses with gain enables a host of new applications
for metallic nanostructures, including low- or no-loss negative-index metamaterials.
We have also predicted and experimentally observed a suppression of SP resonance in metallic nanoparticles embedded in dielectric
host with absorption.
Applied Physics B 01/2007; 86(3):455-460. · 2.19 Impact Factor
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ABSTRACT: The race toward engineering metamaterials comprising of negative refractive indexes in the optical range started with the realization of negative-index materials for gigahertz frequencies six years ago. Sheer miniaturization of the gigahertz resonant structures is one approach. Alternative designs make use of localized plasmon resonant metal nanoparticles or nanoholes in metal films. Following this approach, a negative refractive index has been realized in the optical range very recently. We review these recent results and summarize how to unambiguously retrieve the effective refractive index of thin layers from data accessible to measurements. Numerical simulations show that a composite material comprising of silver strips and a gain-providing material can have a negative refractive index of $-1.3$ and 100% transmission, simultaneously.
IEEE Journal of Selected Topics in Quantum Electronics 12/2006; 12(6):1106-1115. · 3.78 Impact Factor
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ABSTRACT: We have observed the compensation of loss in a metal by a gain in a dielectric medium in the mixture of an Ag aggregate and a Rhodamine 6G dye. The demonstrated sixfold enhancement of the Rayleigh scattering is the evidence of the enhancement of the surface-plasmon resonance. The reported experimental observation facilitates many applications of nanoplasmonics.
Optics Letters 11/2006; 31(20):3022-4. · 3.40 Impact Factor
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ABSTRACT: We have observed the compensation of loss in metal by gain in interfacing dielectric in the mixture of aggregated silver nanoparticles and rhodamine 6G dye. The demonstrated six-fold enhancement of the Rayleigh scattering is the evidence of the increase of the quality factor of the surface plasmon (SP) resonance. The reported experimental observation paves the road to many practical applications of nanoplasmonics. We have also predicted and experimentally observed a suppression of the surface SP resonance in metallic nanoparticles embedded in a dielectric host with absorption.
01/2006;
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ABSTRACT: Comprehensive studies for a periodic array of gold nanorod pairs demonstrate its unique optical properties, including a negative refractive index in the optical range. (© 2006 by Astro, Ltd. Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA)
Laser Physics Letters 12/2005; 3(1):49 - 55. · 9.97 Impact Factor
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ABSTRACT: We have shown that excitation and emission spectra and emission kinetics of Eu: Y2O3 powder can be influenced by aggregated Ag nanoparticles. This demonstrates that basic physical and spectroscopic properties of novel advanced luminescent and gain media and, in particular, materials for random lasers can be engineered at the nanoscale level.
Journal of Modern Optics 11/2005; 52(16):2331-2341. · 1.17 Impact Factor
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ABSTRACT: Specially designed metal-dielectric composites can have a negative refractive index in the optical range. Specifically, it is shown that arrays of single and paired nanorods can provide such negative refraction. For pairs of metal rods, a negative refractive index has been observed at 1.5 micrometer. The inverted structure of paired voids in metal films may also exhibit a negative refractive index. A similar effect can be accomplished with metal strips in which the refractive index can reach -2. The refractive index retrieval procedure and the critical role of light phases in determining the refractive index is discussed. Comment: 39 pages, 17 figures, 24 equations
09/2005;
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ABSTRACT: We have found that R6G laser dye in a concentration of 0.1 g l−1 mixed with a solution of aggregated silver nanoparticles exhibits a new emission band with a maximum at 612 nm. This band does not exist in pure dye of comparable concentration or in a mixture of dye with a solution of single silver nanoparticles. A qualitatively similar red-shifted emission band is observed in pure R6G dye at very high concentration (3.8 or 16.7 g l−1). In both cases, no changes occur to the shapes of the absorption spectra of the dye. We explain the observed spectral changes in terms of J-aggregates of R6G molecules whose formation is probable in the presence of Ag aggregates with a complicated surface structure and is much less likely in the case of adsorption of dye molecules on single Ag nanoparticles. Alternatively, many features observed in the experiment can be explained by an enhancement of the rates of spontaneous radiative transitions in the proximity of metallic particles, which is due to a modification of the local density of electromagnetic modes in the vicinity of metal surfaces at energies resonant with surface plasmon resonances.
Journal of Optics A Pure and Applied Optics 01/2005; 7(2):S219. · 1.92 Impact Factor
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ABSTRACT: Summary form only given. The adaptive property of e-beam evaporated silver films has been studied and employed for protein sensing with surface-enhanced Raman scattering (SERS). Our approach for sensing proteins is based on adaptive silver films (ASFs); the method allows fine nanostructure rearrangement under protein deposition that makes it possible to soft-adsorb proteins on the metal surface and to form aggregates of nanoparticles which are optimal for SERS. We demonstrate that adaptive nanostructured films can be used for the observation of differences in SERS spectra of recombinant human insulin and insulin lispro at sub-monolayer protein surface densities and provide macroscopic enhancement factor of about 3×10<sup>6</sup> . Since human insulin and its analog have the same set of side chains and differ only in conformational states, the observed difference indicates the preservation of the conformational state with the use of adaptive metal substrates. Direct, label-free detection of antibody-antigen binding at a monolayer protein concentration has been also demonstrated, using SERS detection on adaptive silver films. This includes evidence of distinct SERS spectral changes upon antigen-antibody binding and independent biochemical sandwich assay validation studies, which confirm that antibodies retain binding properties on ASFs. It is shown that proteins stabilize the ASFs and restructure them so that proteins can preserve their binding activity. We demonstrate the ability to employ various detection methods with one substrate, including label-free SERS, chemiluminescence, fluorescence, and further analysis of protein spot retrieved from the surface.
Lasers and Electro-Optics Society, 2004. LEOS 2004. The 17th Annual Meeting of the IEEE; 12/2004
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ABSTRACT: Owing to the low-loss and high refractive index variations derived from the basic building block of bone structure, we, for the first time to our knowledge, demonstrate coherent random lasing action originated from the bone structure infiltrated with laser dye, revealing that bone tissue is an ideal biological material for random lasing. Our numerical simulation shows that random lasers are extremely sensitive to subtle structural changes even at nanoscales and can potentially be an excellent tool for probing nanoscale structural alterations in real time as a novel spectroscopic modality. (C) 2010 Optical Society of America
Birck and NCN Publications.
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ABSTRACT: The effect of grain boundaries on the electron relaxation rate is significant even for large area noble metal films and more so for plasmonic nanostructures. Optical spectroscopy and X-ray diffraction show a substantial improvement in plasmon resonance quality for square-particle nanoantennas after annealing due to an enlarged grain size from 22 to 40 nm and improved grain boundaries described by the electron relfection coefficient. The electron relaxation rate due to the grains is shown to decrease by a factor of 3.2.
Birck and NCN Publications.
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ABSTRACT: We review recent progress in optical metamaterials and demonstrate our sample with negative index behavior at the shortest wavelength so far (710 nm). We discuss the impact of fabrication limitations on the performance of metamaterials.
Birck and NCN Publications.
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[show abstract]
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ABSTRACT: We have employed a parallelized 3D FDTD (finite-difference time-domain) solver to study the electromagnetic properties of random, semicontinuous, metal films. The structural features of the simulated geometries are exact copies of the fabricated films and are obtained from SEM images of the films themselves. The simulation results show good agreement with the experimentally observed far-field spectra, allowing us to also study the nonlinear moments of the optical responses for these realistic nanostructures. These results help to further our understanding of the details of the electromagnetic response of randomly structured metal films. Our results can also be applied in the optimization of random metal nanostructures and in the design of surface-enhanced spectroscopies and other plasmonic applications.
Birck and NCN Publications.
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ABSTRACT: Near-field, broadband optical spectroscopy of metamaterials is reported. A compact, easy to assemble supercontinuum light source, coupled with a near-field scanning optical microscope and spectrometer provide the means to locally probe the spectral response of a nanorod metamaterial sample. Spectral maps of near-field transmittance are obtained for the spectral range from 500 to 950 nm. In comparison to far-field measurement, the average of the near-field mappings shows a significant increase in transmittance. The uniqueness of the spectral maps and the increased transmittance indicates a strong nanoantenna effect between the sample and the plasmonic near-field aperture.
Birck and NCN Publications.
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ABSTRACT: This work is concerned with the experimental demonstration of a dual-band negative index metamaterial. The sample is double negative (showing both a negative effective permeability and a negative effective permittivity) for linearly polarized light with a wavelength between 799 and 818 nm, and the real part of its refractive index is approximately - 1.0 at 813 nm. The ratio of -Re(n) /Im(n) is close to 1.3 at 813 nm. For an orthogonal polarization, the same sample also exhibits a negative refractive index in the visible (at 772 nm). The spectroscopic measurements of the material are in good agreement with the results obtained from a finite-element electromagnetic solver for the actual geometry of the fabricated sample at both polarizations.
Birck and NCN Publications.
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ABSTRACT: Periodic arrays of paired and single gold nanorods were imaged in the near field using reflection and transmission modes of a near-field scanning optical microscope at various wavelengths and polarizations of light in the visible range. The paired nanorods act like nanoantenna, and an array of them was initially designed as a negative-index material for the near infrared. Reverse contrast in reflection and transmission images is observed under illumination from the small aperture of a metal-coated fiber probe. By changing the relative orientation of the rods to the polarization, the reverse contrast switches to the normal contrast of near-field imaging. Coupling between the aperture and the nanorod array makes the contrast higher. Transmission through the aperture is enhanced if the aperture probe is positioned between the nanorods. The average near-field transmission exhibits an opposite sign of anisotropy relative to the far-field case. Aperture probes with larger diameters always show normal imaging contrast. The results demonstrate that the broad angular spectra of small-aperture sources play a crucial role in near-field interactions with nanorod arrays. The results also show that angular redistributions of these spectra after transmission or reflection from the nanorod array are likely due to excitation of localized and propagating plasmons.
Birck and NCN Publications.
