Search

We report the fabrication of textured metal surfaces by ultrafast laser processing and its optical property characterization by measurement of reflection and scattering as a function of angle and wavelength. The ultrafast laser textured metal surface reflection combined with scattering can be reduced to low values of ~3% over a broad spectral and angular range. Furthermore, it is shown that surface optical reflection and scattering can be varied by parameters like laser fluence, number of laser pulses, and coating the textured surfaces with suitable absorbers. It is also shown that ultrafast laser textured metal surfaces can have low surface reflection and scattering properties even at high temperatures ( OCIS codes: 350.3390, 290.0290, 240.0240, 230.0230, 220.0220.

Plasmonic metal nanoparticles (NPs) exhibit size, shape, and composition-dependent optical properties and have been studied extensively in the field of biosensing, but wide applications so far are limited by a lack of both highly sensitive and quantitative yet cost-effective optical detection schemes. We present a single molecule biosensing method based on color differentiation of scattered light between single plasmonic NPs and DNA hybridization-induced NP aggregates. With a seed-mediated NP growth method and a fast DNA modification method, highly stable, spectrally uniform and monodisperse Au NP (40 nm) and Au/Ag/Au composite NP (33 nm) probes were successfully prepared. Through theoretical calculations, single NP spectral measurements, and real lime single-NP tracking experiments, we show that binding of a single target molecule between two NP probes can be recognized without separation from the unbound NPs by simply using a darkfield microscope equipped with a conventional light source and a color charge coupled device (CCD) camera. The detection limit of this homogeneous assay reached 0.02 pM. As an initial demonstration of multiplexed sensing at the single NP level, we used Au NPs and Au/ Ag/Au composite NPs as different color probes. This scheme could be potentially applied to other areas such as multiplexed immunoassay, single cell analysis, and real time biomolecule interaction studies. 10.1021/ac101018v

We analyze the focusing properties of Fresnel zone plates fabricated over steel tapes using laser ablation. Our intention is to implement the use of micro-optical elements when the use of conventional chrome-glass elements is not indicated. Because of the manufacture process, the surface presents a certain anisotropic roughness, which reduces the focusing properties. First, we develop numerical simulations by means of the Rayleigh--Sommerfeld approach, showing how roughness in both levels of the Fresnel zone plate affects the focalization of the lens. We also manufacture Fresnel zone plates over steel tape, and perform experimental verification that corroborates the numerical results. [c] 2010 Optical Society of America OCIS codes: 050.1965, 240.3990, 240.5770.

A metal slit array arranged along a semicircular surface achieving subwavelength optical beam focusing along the lateral direction is proposed. Taking into consideration surface plasmon polaritons that pass through a metal slit array, we design the array with a curvature. By use of a genetic algorithm, the size of the metal slit and the corresponding curvature are to be determined. Based on our metal slit array configuration, the full width at half-maximum can be achieved on a subwavelength scale. OCIS codes: 240.6680, 230.3120.

We analyzed and experimentally tested a metal--dielectric composite waveguide structure. After coating the surface of the metal layer in the Kretschmann attenuated total internal reflection configuration with a dielectric layer, we explain the coupling of incident light into the coated layer. After finding the dispersion relationships for the layered media including the metal--dielectric composite waveguide, we can determine a solution for its existance in a complex domain. By inscribing a periodic grating structure in the dielectric layer of the metal--dielectric composite waveguide, we experimentally verify the coupling of incident light on the metal--dielectric composite waveguide structure and propose its application for use as a wavelength-band selection filter. OCIS codes: 240.6680, 230.7400, 230.7408.

We report the focusing of a normally incident plane wave of 405 nm through a Ag/dielectric annular ring structure, using finite-difference time domain analysis. We first study the dependency of the focusing efficiency on slit width when the incident wave is transmitted through a single ring whose slit is filled with a dielectric. Then, light focusing by the multiple-ring structure is investigated as a function of the dielectric thickness. It is observed that the focusing is tunable between near-field and quasi-far-field regimes in the Ag/dielectric layered annular ring structure. Also, the focal intensities are remarkably enhanced by the addition of the dielectric layer, showing a Fabry--Perot-like resonance with respect to the thickness of the dielectric layer. The controllable near-field and far-field focusing offers more flexibility for applications of future nano-optic devices. [c] 2010 Optical Society of America OCIS codes: 240.6680, 240.0240.

Composite films consisting of a ceramic matrix with embedded metal nanoparticles have received increased interest due to their numerous potential applications in the field of optics and optoelectronics. Numerous studies have been dedicated to the fabrication of these composite materials and it has been shown that nanocermet films can be obtained by successive deposition of alternate dielectric and metal films of thicknesses opportunely chosen. In this case, stacks of dielectric layers alternated with layers of metal nanoclusters (NCs) are obtained. However, until now, optical characterization of these kinds of multilayer stack has been used to retrieve mainly qualitative information on the dimension, shape, and geometric distribution of nanoparticles inside the dielectric matrix. An easy-to-handle model that quantitatively links the optical properties to the main features of the NCs embedded in the matrix is presented. This model can be applied to multilayer stacks of dielectric layers alternated with metal NC layers and is shown to be a valid alternative to a recently published model [Nanotechnology 19, 125709 (2008)] that was applied to the case of a three-layer structure (dielectric/metal:dielectric/dielectrict. OCIS codes: 310.6860, 240.6680, 160.4236.

Localized surface plasmons of metallic particles of sub-wavelength sizes strongly modify the spectral properties of nearby fluorophores. The enhanced radiative decay rate leads to high fluorescence efficiencies and decreased fluorescence lifetimes. In this report we show that metalenhanced fluorescence generated by the presence of the silver islands on the glass substrate displays high depolarization. Intensifies, lifetimes, and emission anisotropies of several fluorophore protein conjugates have been studied in the absence and presence of metallic nanostructures. Despite highly decreased lifetimes of about 10-fold and immobilization of conjugates on the solid substrate, the observed emission anisotropies for all fluorophores on the metal-enhanced substrate decreased 300-500% compared to that in solution. This observation implies a new generation of fluorescence polarization immunoassays with broad applications because of no restrictions to the lifetime of the probe and the size of labeled biomolecules. The changes in polarization are due to binding that occur on the bioactive surface localized near the metal particles.

By employing a modified Otto's configuration for measuring surface plasmon resonance that has been proposed by Bliokh and his coworkers [Appl. Phys. Lett. 89, 021908 (2006)] we have obtained complex refractive indices of metals at several wavelengths. We demonstrate that the configuration has high potential for obtaining dispersion relations of metal conductors in bulk samples as well as in thin films from the visible to the near-infrared wavelength region. Furthermore, we show that the configuration enables us to obtain the complex refractive indices of metals or a thickness or refractive index of a dielectric layer on the metal at different points simultaneously. We have constructed a measurement system and carried out basic experiments. The experimental results agreed well with numerically simulated values or published ones. OCIS codes: 240.6680, 310.6850, 120.6680.

The possibility of constructing an optical sensor for temperature monitoring based on the Goos-Hanchen (GH) effect is explored using a theoretical model. This model considers the lateral shift of the incident beam upon reflection from a metal-dielectric interface, with the shift becoming a function of temperature due mainly to the temperature dependence of the optical properties of the metal. It is found that such a sensor can be most effective by using long wavelength p-polarized incident light at almost grazing incidence onto the metal, where significant variation of negative GH shifts can be observed as a function of the temperature. OCIS codes: 240.0240, 260.3910.

The synthesis, structural, photophysical and second-order nonlinear optical (NLO) properties of a novel lanthanide terpyridyl-like complex family LLn[(N[O.sub.3]).sub.3] (Ln = La, Gd, Dy, Yb and Y) are described. The quadratic hyperpolarizability coefficient beta, measured by the harmonic light scattering (HLS) method, is found to be dependent on the nature of the metal and the examination of yttrium unambiguously has confirmed the contribution of metal f electrons to the NLO activity.

In the field of industrial vision, the three-dimensional inspection of highly reflective metallic objects is still a delicate task. We deal with a new automated three-dimensional inspection system based on polarization analysis. We first present an extension of the shape-from-polarization method for dielectric surfaces to metallic surfaces. Then, we describe what we believe to be a new way of solving the ambiguity concerning the normal orientation with an active lighting system. Finally, applications to shape-defect detection are discussed, and the efficiency of the system to discriminate defects on specular metallic objects made by stamping and polishing is presented. OCIS code: 110.6880

Anomalous field enhancement occurs between two-plasmon-resonant surfaces. This model is expected to be useful for metal surfaces having roughness.

The dependence of the magnetically resonant transmission on the structural parameters is studied. The optimized structure of the double-ring metamaterial is used for exploring the terahertz response with all the sizes scaled down simultaneously.

Monte Carlo simulations based on three-dimensional (3D) ray tracing was used to study the laser absorptance of rough surfaces and determine the influence of multiple scattering, shadowing, and the Fresnel-equnation based angle dependence. The results showed that the absorptance increases or decreases with increasing roughness depends on the laction of the Brewster angle of the particular metal/wavelength combination involved.

The effect of [N.sub.2], Ar and [O.sub.2] plasma treatments on the surface properties of metals is described. Synchrotron radiation photoemission spectroscopy has showed that the work function has increased after [N.sub.2], Ar and [O.sub.2] plasma treatments in sequence, which is due to the reduction of carbon atoms and the formation of O-rich surface in [O.sub.2] plasma case.

Ray tracing using Nd:YAG laser is used to study the absorption of light by smooth and rough surfaces. The results show that in light incident at a tangent to the surface, the absorptance is found to rise, fall, and rise again with increase in surface roughness due to multiple scattering.

Electronic excitations have a profound impact on molecular motion induced by femtosecond laser pulses and play a large role in catalytic reaction as well as in spin transport within bulk metals, across interfaces, and at surfaces. At metal surfaces, in addition to bulk electron states, new electron states arise and these new states can be classified as intrinsic surface states and image-potential states.

Ultrashort laser pulses are examined as a means for the generation of deep narrow holes in metal samples, where the drilling is observed in two stages. The coupling of light energy to the sample during the second stage of drilling and its polarization dependence determine the final hole shape.

The proof-of-principle of a new technique, which significantly enhances the luminescence intensity of chemiluminescence species and shortens the detection times by low power microwave heating in the presence of silver nanoparticles called Microwave-Triggered Metal-Enhanced Chemiluminescence (MT-MEC) is presented. The applicability of the MT-MEC technique for multiple chemiluminescent species emitting at different wavelengths is shown which could be extended to any chemiluminescent detection system currently in use.