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We studied by FDTD computer simulations the dependence of the surface plasmon resonances in linearly arranged gold nanospheres on incident light polarization, spheres number and diameter, and interparticle gap. The observed scattering spectra of large particles show a particularly interesting behaviour, with coupled plasmon resonances that can be either red or blue shifting with the modification of the interparticle gap. The sensitivity of the various observed coupled plasmon modes to refractive index variations is then evaluated. [ABSTRACT FROM AUTHOR]

Simultaneous field- and aperture-plane (back-focal plane, BFP) imaging enriches the information content of fluorescence microscopy. In addition to the usual density and concentration maps of sample-plane images, BFP images provide information on the surface proximity and orientation of molecular fluorophores. They also give access to the refractive index of the fluorophore-embedding medium. However, in the high-NA, wide-field detection geometry commonly used in single-molecule localisation microscopies, such measurements are averaged over all fluorophores present in the objective's field of view, thus limiting spatial resolution and specificity. We here solve this problem and demonstrate how an oblique, variable-angle, coherent ring illumination can be used to generate a Bessel beam that - for supercritical excitation angles - produces an evanescent needle of light. Scanning the sample through the this evanescent needle enables us to acquire combined sample-plane and BFP images with sub-diffraction resolution and axial localisation precision. Background, resolution and polarisation considerations will be discussed. [ABSTRACT FROM AUTHOR]

The refractometric analysis of ethanol-water mixtures is hampered because this type of binary solution does not present a linear behaviour. In this work it is proposed a multimode Graded-Index Fiber (GIF) tip sensor for the measurement of ethanol in binary liquid solutions of ethanol-water. The probe is fabricated by fusion-splicing a 500 µm GIF to a Single Mode Fiber (SMF) and it operates as a refractometric sensor in reflection. Samples of ethanol-water mixtures were measured at different temperatures (20°C to 60°C) to evaluate the probe's capability to detect variations in ethanol refractive index. The samples have different % (v/v) of ethanol, in a range between 0% and 100%. [ABSTRACT FROM AUTHOR]

Polymer optical fibers (POFs) have many advantages. Because of their biocompatibility, they can be used as biosensors. In this paper, we report three types of refractometric sensors in poly(methyl methacrylate) PMMA POFs. They are based on different technologies, i.e. tilted fiber Bragg gratings (TFBGs), TFBGs with a thin gold layer and non-clad POFs. All the three sensors are sensitive to surrounding refractive indices showing great potential for (bio)chemical sensing. [ABSTRACT FROM AUTHOR]

The work is devoted to the numerical and experimental study of surface plasmon resonance in a bent singlemode optical fiber with metalized cladding. It was shown that with a proper combination of metal film thickness and bend radius one can achieve coupling between fundamental and surface plasmon modes through an intermediary of whispering gallery mode supported by the bent fiber's optical cladding. This brings about a dip in the transmission spectrum of the fiber at the resonant wavelength which depends strongly on the external medium refractive index, so that refractometric measurements can be performed with a sensitivity of ~5 μm/RIU and resolution ~4·10-6. [ABSTRACT FROM AUTHOR]

Faultless processing of thermoset polymers in demanding applications requires a profound mastering of the curing kinetics considering both the physico-chemical changes in the transition from the liquid to the solid state and the consolidation of the polymers network in the diffusion controlled curing regime past the gel point. Especially in adhesive joints shrinkage stress occurring at an early state of the curing process under confined conditions is likely to cause defects due to local debonding and thus reduce their strength and durability1. Rheometry is considered the method of choice to investigate the change of elastic and viscous properties in the progress of curing. Drawbacks however relate to experimental challenges in accessing the full range of kinetic parameters of thermoset resins with low initial viscosity from the very beginning of the curing reaction to the post-cure consolidation of the polymer due to the formation of secondary chemical bonds. Therefore the scope of this study was to interrelate rheological data with results from in-situ measurements of the shrinkage stress formation in adhesive joints and with the change of refractive index in the progress of curing. This combination of different methods has shown to be valuable in gaining advanced insight into the kinetics of the curing reaction. The experimental results are based on a multi component thermoset epoxy-amine adhesive. [ABSTRACT FROM AUTHOR]

In this work, four U-shaped Plastic Optical Fiber (POF) sensors manufactured with a specially developed machine are characterized and implemented for refractometry. The measurement set-up consists of an LED and a photodiode connected to the ends of the fiber, and the signal is detected by a Lock-in Amplifier implemented in Matlab®. The calibration process led to the evaluation of the sensitivity, accuracy and repeatability by using solutions of sucrose for obtaining refractive indexes (RI) in the range 1.33 - 1.39. [ABSTRACT FROM AUTHOR]

We report on a functional, highly reproducible and cost effective sensing platform based on photonic crystal fibers (PCFs). The platform consists of a centimeter-length segment of an index-guiding PCF fusion spliced to standard single mode fibers (SMFs). The voids of the PCF are intentionally sealed over an adequate length in the PCF-SMF interfaces. A microscopic collapsed region in the PCF induces a mode field mismatch which combined with the axial symmetry of the structure allow the efficient excitation and recombination or overlapping of azimuthal symmetric modes in the PCF. The transmission or reflection spectrum of the devices exhibits a high-visibility interference pattern or a single, profound and narrow notch. The interference pattern or the notch position shifts when the length of the PCF experiences microelongations or when liquids or coatings are present on the PCF surface. Thus, the platform here proposed can be useful for sensing diverse parameters such as strain, vibration, pressure, humidity, refractive index, gases, etc. Unlike other PCF-based sensing platforms the multiplexing of the devices here proposed is simple for which it is possible to implement PCF-based sensor arrays or networks. [ABSTRACT FROM PUBLISHER]

The opto-fluidics systems can be used for label free refractometric and biosensensing applications. In this work transmission properties of one-dimensional polycarbonate-liquid photonic arrays are studied, where methanol and ethanol were proposed as liquid components. The band structure and the transmission spectrum were calculated using the transference matrix method, in which we consider the dispersion relation for the refractive index n(w) of each material in the visible range. Using lattice parameters of 1 µm, 10 µm, and 4 µm, we obtained forbidden bandgaps in the visible region. When lattice parameters of 1000 µm were considered, we obtained several narrow bandgaps in the visible range. [ABSTRACT FROM AUTHOR]