1,721,184 research outputs found
ONE- TWO- AND THREE-DIMENSIONAL PHOTONIC CRYSTALS: OPTICAL PROPERTIES AND APPLICATIONS
No full textIn the last decade, photonic crystals (PhC) - namely nanostructured materials with a periodic dielectric function - have opened new possibilities in the world of photonic devices, due to their unique properties that allow to control and manipulate light propagation. In order to fully understand the optical properties of PhC structures spectroscopic techniques like transmittance, reflectance and interferometry have been specifically tuned to provide a thorough characterization of the photonic band structure, light propagation and attenuation. In addition efficient theoretical tools have been developed that allow the design of PhC structures and the calculation of their optical response, which fully accounts for the experimental observations. Recent interesting results are reported on “slow-wave” propagation in 1D porous silicon coupled microcavities, as well as strong enhancement and spectral modification of emission in 2D waveguide-based PhC embedding active materials, and unusual propagation and diffraction effects in 3D polystyrene opals
Photonic and plasmonic nanodevices for enhancing light-matter interaction and biosensing functionalities
No full textNoble metal nanowaveguides supporting plasmon polariton modes are able to localize the optical fields at nanometer level for high sensitivity
biochemical sensing devices. Here we report on the design and fabrication of a novel photonic-plasmonic device which demonstrates labelfree
detection capabilities on single inorganic nanoparticles and on monolayers of organic compounds. In any case, we determine the Raman
scattering signal enhancement and the device detection limits that reach a number of molecules between 10 and 250. The device can be
straightforwardly integrated in a scanning probe apparatus with the possibility to match topographic and label-free spectroscopic information
in a wide range of geometries
Optical properties of materials
No full textStarting from Maxwell equations and constitutive equations of a medium we consider the linear macroscopic optical response for homogeneous, isotropic, non-magnetic materials. The complex dielectric function and complex refractive index are derived with their connections with optical reflectance, transmittance and absorptance, for both unpolarized and polarized light. A few selected examples of optical response for solids (metals, semiconductors and insulators) are presented, together with the simplest classical and quantum models producing analytical expressions for the optical structures observed in experimental spectra. Analytical models give insights into optical response of materials and heterostructures, and should be used both to fit experimental data and simulate performances of electronic and photonic devices
Methods for glass surface coating with functional Self Assembled Monolayers
No full textA modified approach is presented to efficiently coat flat galss surfaces with function molecules. An optical method to check the efficiency of the coating is also presente
Early stages of growth of Ge quantum dots
No full textThe present work is concentrated on the investigation of the initial stages of growth of Ge nanoparticles embedded in an amorphous A1203 matrix on suitable substrates. The growth technique is based on self-organization processes related to the balance of the interface energies involved. Combined data from complementary optical techniques (absorption, Raman scattering, spectroscopic ellipsometry) give evidence of a behaviour which can be ascribed to the existence of a wetting layer, not detectable by conventional transmission microscopy
Optical Functions from 0.02 to 6 eV of AlGaSb/GaSb Epitaxial Layers
No full textThe complex refractive index = n+ik and the dielectric function = ε1+iε2 at room temperature of AlxGa1−xSb films with 0 ⩽ x ⩽ 0.5, grown by molecular beam epitaxy on a GaSb substrate, were determined from 0.02 to 6 eV by using the complementary data from fast Fourier transform far-infrared, dispersive, and ellipsometric spectrometry. The effect of the native oxide was accounted for and the self-consistency of the optical functions was checked in the framework of the Kramers–Kronig causality relations. In the restrahlen region the dielectric function was well fitted by classical Lorentz oscillators; in the transparent region below the fundamental gap E0, the refractive index was modeled by a Sellmeier dispersion relation, and in the interband region the dielectric function near the critical points was analyzed through standard line shapes. Interpolating the fitting parameters or the interband dielectric spectra, it was possible to obtain the optical functions for any concentration x between 0.0 and 0.5
Understanding metal nanoparticles optical behavior: a case study
No full textThe nonlinear interaction between materials based on metallic
nanoparticles and strong electric ̄elds such as the one produced
by laser pulsed radiation produces signi ̄cant response ampli ̄cation whenever electronic or photonic system resonances are being excited. In particular, second harmonic radiation excited by pulsed lasers in the near infrared can be generated in metal nanoparticles with e±ciencies far exceeding those of corresponding bulk materials. In this paper,
experimental results are presented for two di®erent physical systems, namely Au nanoparticles in aqueous solutions and Ga nanoparticle monolayers embedded in dielectric matrices with mean radii in the nanometer range. Measurements of second harmonic generated radiation in the two systems in di®erent geometries and their dependence on various physical parameters shed light on the response mechanisms to electromagnetic radiation
Demonstration of fluorescence enhancement: via Bloch surface waves in all-polymer multilayer structures
Full text linkAn all-polymer photonic structure constituted by a distributed Bragg reflector topped with an ultrathin fluorescent polymer film has been studied. A Bloch surface wave resonance has been exploited to improve pumping efficiency. A strongly polarization and angle dependent fluorescence signal is found with respect to the light pumping beam and the emitted wavelength. Matching the most favorable condition for the pump coupling and the collection geometry, the signal obtained from the structure appears to be two orders of magnitude larger than the one of the bare emitting film
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