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Unusual optical properties of laser-ablated metal surfaces arise from the excitation of local plasmon resonances in nano- and microstructures produced by laser-processing and from the mutual interaction of those structures through surface plasmon polariton (SPP) waves. This interaction provides a synergistic effect, which can make the optical properties of the composite nanostructure drastically different from the properties of its elements. At the same time, the prediction and analysis of these properties are hampered by the complexity of the analytical solution to the problem of SPP excitation by surface objects of arbitrary configuration. Such a problem can be reduced to a simpler one if one considers the geometry of a structured surface as a superposition of harmonic Fourier components. Therefore, the analytical solution to the problem of surface plasmon polariton excitation through the scattering of light by a sinusoidally perturbed plasmonic metal/vacuum boundary becomes very important. In this work, we show that this problem can be solved using a well-known method for calculating guided-mode amplitudes in the presence of current sources, which is used widely in the waveguide theory. The calculations are carried out for the simplest 2D cases of (1) a sinusoidal current of finite length and (2) a finite-length sinusoidal corrugation on a plasmonic metal surface illuminated by a normally incident plane wave. The analytical solution is compared with the results of numerical simulations. It is shown that, in the first case, the analytical and numerical solutions agree almost perfectly. In the second case, the analytical solution correctly predicts the optimum height of the corrugation x opt , providing the maximum SPP excitation efficiency. At the same time, the analytical and numerical values of the SPP amplitude agree very well when the corrugation height x turns out to be x ≪ x opt or x ≫ x opt (at least up to 3 x opt ); at x = x opt , the mismatch of those does not exceed 25%. The limitations of the analytical model leading to such a mismatch are discussed. We believe that the presented approach is useful for modeling various phenomena associated with SPP excitation. [ABSTRACT FROM AUTHOR]

We present a numerical and experimental study of resonance splitting in the transmission and reflection spectra of the Fabry–Perot resonator made of a bent section of a conventional single-mode optical fiber with metallized end faces. We show the splitting to be similar in nature to the well-known Autler–Townes effect and to arise from the strong coupling between the core mode and cladding whispering gallery mode of the bent fiber. The effect of all major parameters of the bent resonator on the splitting of its resonances is demonstrated. Potential applications of the observed effects in the field of precision optical refractometry as well as further research directions are discussed. [ABSTRACT FROM AUTHOR]

We present a numerical study comparing three configurations of the waveguide-based surface plasmon resonance refractometer: without a buffer layer based on the excitation of the bulk surface plasmon mode, and with a buffer layer using the symmetric (long-range) and antisymmetric (short-range) plasmon modes. Optimal conditions ensuring the sharpest resonant dip in the refractometer's transmission spectrum are identified. Relative merits of various configurations in terms of the figure-of-merit parameter, local sensitivity to refractive index variations near the metal film, and the size of the sensing element are quantified and discussed. [ABSTRACT FROM AUTHOR]

We present a numerical and experimental study of surface plasmon resonance (SPR) excitation in a bent single-mode optical fiber with metalized cladding. It is shown that with a suitable combination of bend radius and metal film thickness surface plasmon waves can be excited in the film as a result of coupling between fundamental and surface plasmon modes via whispering gallery modes supported by the bent fiber cladding. The coupling brings about a dip in the transmission spectrum at the resonant wavelength which is strongly dependent on the ambient refractive index. This enables one to build a fiber optic SPR-refractometer with a standard single-mode fiber without breaking integrity of the fiber or using any additional elements. Refractometric sensitivity of -5µmper refractive index unit and resolution of -4*10-6 are experimentally demonstrated for the measured refractive index around 1.43. The reported results may find wide application in bio- and chemosensing. [ABSTRACT FROM AUTHOR]

An experimental study is presented of the application of fiber Bragg grating (FBG) interrogation method based on optical time-domain reflectometery (OTDR) to monitoring strain in bent reinforced concrete beams. The results obtained with the OTDR-based method are shown to agree well with the direct spectral measurements. Strain sensitivity, resolution and measurement range amounted to 0.0028 dB/μstrain; 30 μstrain; 4000 μstrain, correspondingly. Significant differences are observed in surface and inner deformations of the test beams which can be attributed to different mechanical properties of concrete and steel reinforcement. The prospects of using OTDR-based FBG interrogation technique in real-life applications are discussed. [ABSTRACT FROM AUTHOR]

Since surface plasmon polaritons (SPPs) are surface waves, they cannot be excited by an incident plane wave, because free-space photons do not possess a sufficient in-plane momentum. Phase matching between the incident light and SPP can be achieved using a high-refractive-index prism, grating, or nanoantennas. In this work, we found an expression for the amplitude of SPP excited by an arbitrary 3D current distribution placed near a metal interface. The developed method is based on the well-known technique used in waveguide theory that enables finding the amplitudes of waveguide modes excited by the external currents. It reduces the SPP excitation problem to the summation of the set of emitters. As a particular example, we considered a spherical dipole nanoantenna on a metal substrate illuminated by a normally incident plane wave. The analytical calculations were in good agreement with the full-wave numerical simulations. [ABSTRACT FROM AUTHOR]

We demonstrate a multi-purpose plasmonic sensor based on a nanovoid array fabricated via inexpensive and highly-reproducible direct femtosecond laser patterning of thin glass-supported Au films. The proposed nanovoid array exhibits near-IR surface plasmon (SP) resonances, which can be excited under normal incidence and optimised for specific applications by tailoring the array periodicity, as well as the nanovoid geometric shape. The fabricated SP sensor offers competitive sensitivity of ≈ 1600 nm/RIU at a figure of merit of 12 in bulk refractive index tests, as well as allows for identification of gases and ultra-thin analyte layers, making the sensor particularly useful for common bioassay experiments. Moreover, isolated nanovoids support strong electromagnetic field enhancement at lattice SP resonance wavelength, allowing for label-free molecular identification via surface-enhanced vibration spectroscopy. [ABSTRACT FROM AUTHOR]

We demonstrate analytically and numerically that the detection of the spectral response of a single spherical Au nanoantenna allows one to map very small (down to 5·10(-4) RIU) variations of the refractive index of an optically transparent sample. Spectral shift of the dipole local plasmon resonance wavelength of the nanoantenna and the spectral sensitivity of the method developed was estimated by using simple analytical quasi-static model. A pointed scanning probe based on fiber microaxicon with the Au spherical nanoantenna attached to its tip was proposed to realize the RI mapping method. Finite-difference time-domain numerical simulations of the spectral properties of the proposed probe are in good agreement with the theoretical quasi-electrostatic estimations for a radius of the nanoantenna not exceeding the skin depth of Au.