Search results for "Grating"
showing 10 items of 366 documents
Rigid polymer materials with hologram enhancement by molecular diffusion
2003
The principle of diffusional enhancement has been embodied in the rigid glassy polymer with phenanthrenequinone able to photochemically attach to surrounding macromolecules, thus forming a permanent grating. Owing to material stiffness, it does not suffer from shrinkage and can be made very thick; serving a basis for very stable spectrally selective elements. Replacement of commonly used acrylic glass by polycarbonate ensures further significant improvement of performance and stability of 3D holographic optical elements and memories.
Scale dependent diffusion in latex films studied by photoinduced grating relaxation technique
2003
The transition from an aqueous dispersion of polyacrylate latices into a homogeneous polymer film on drying has been studied by monitoring the diffusion of hydrophobic and hydrophilic photochromic molecular probes with the help of a holographic grating relaxation (forced Rayleigh scattering) technique. Experiments with the hydrophobic probe in wet films result in an unusual spatial scale-dependence of the apparent diffusion coefficient that degenerates into a normal scale-independent diffusion coefficient as the film dries. Employment of a two-state diffusion model allows extracting the diffusion coefficients and mean displacements of the tracer in the polymer cores of the latex particles a…
Entanglement in polystyrene detected by translational diffusion of photo-labeled molecules
1988
Mesure des coefficients de diffusion de polystyrenes marques et comparaison avec une equation phenomenologique reliant la masse moleculaire critique entre les enchevetrements Mc a ces masses moleculaires respectives de la chaine diffusant et de la matrice. Comparaison avec les theories recentes
Measurement of the strain-optic coefficients of PMMA from 800 to 2000 nm
2020
The strain-optic coefficients of PMMA are measured in a broad wavelength range from 800 to 2000 nm. The sensitivity of the azimuthal whispering gallery mode resonances to the strain is exploited to measure the strain-optic coefficients of PMMA micro-rods. The technique is based on measuring the wavelength shift of the resonances of both polarizations states, the TE and TM, when an axial strain is applied to the polymer rods. This method enables the determination of the strain-optic coefficients of the material in a broad wavelength range. In particular, in the near-infrared range, the PMMA exhibits negligible dispersion and anisotropy, and the strain-optic coefficients show constant values …
Polymers films with indandione derivatives as alternatives to azobenzene polymers for optical patterning
2008
Surface relief gratings (SRGs) on organic thin films are studied extensively for both scientific interest and in relevance to the applications. Among the chromophores being used the azobenzenes showed the best performance, but the use of alternative photo-sensitive groups provides better general understanding of the phenomena. A thermodynamic theory and molecular dynamics simulations of photoinduced effects are discussed. In this study we use indandione derivatives, known as promising materials for photonics applications, as an alternative to the azobenzenes. We consider their photoreactions when incorporated into a polymer film. One of interesting features is the spectral dependence of the…
La teoria della vergogna reintegrativa di Braithwaite
2021
Riflessione sulla teoria elaborata da John Braithwaite nota con il nome di teoria della vergogna reintegrativa (reintegrative shaming) che rappresenta l’esempio teoria integrata generale (che si rivolge dunque a più condotte criminali) e di tipo «fianco a fianco» (side-by-side). Reflection on the theory developed by John Braithwaite known as the theory of reintegrative shaming which represents the example general integrated theory (which therefore addresses several criminal conducts) and of the "side-by-side" type (side-by -side).
Diseño físico-matemático de un espectrómetro óptico
2016
[EN] This work presents the design and construction of a spectrometer made in the laboratory and the development of mathematical models needed to process and analyze the acquired spectrum. For modeling functions it has been used LabVIEW program. The aim is to bring this type of instrumentation to engineering students from both, physical and mathematical point of view. The application has been successfully integrated in the learning strategies of the course Sensores Fisicos, Master Universitario en Sensores Para Aplicaciones Industriales at the Universitat Politecnica de Valencia. As an example, we have characterized different light sources emitting in different regions of the electromagneti…
Transient guided-mode resonance metasurfaces with phase-transition materials
2023
We investigate transient, photo-thermally induced metasurface effects in a planar thin-film multilayer based on a phase-transition material. Illumination of a properly designed multilayer with two obliquely incident and phase-coherent pulsed pumps induces a transient and reversible temperature pattern in the phase-transition layer. The deep periodic modulation of the refractive index, caused by the interfering pumps, produces a transient Fano-like spectral feature associated with a guided-mode resonance. A coupled opto-thermal model is employed to analyze the temporal dynamics of the transient metasurface and to evaluate its speed and modulation capabilities. Using near-infrared pump pulses…
Fabrication-friendly polarization-sensitive plasmonic grating for optimal surface-enhanced Raman spectroscopy
2020
Plasmonic nanostructures are widely utilized in surface-enhanced Raman spectroscopy (SERS) from ultraviolet to near-infrared applications. Periodic nanoplasmonic systems such as plasmonic gratings are of great interest as SERS-active substrates due to their strong polarization dependence and ease of fabrication. In this work, we modelled a silver grating that manifests a subradiant plasmonic resonance as a dip in its reflectivity with significant near-field enhancement only for transverse-magnetic (TM) polarization of light. We investigated the role of its fill factor, commonly defined as a ratio between the width of the grating groove and the grating period, on the SERS enhancement. We des…
Generation of programmable 3D optical vortex structures through devil’s vortex-lens arrays
2013
Different spatial distributions of optical vortices have been generated and characterized by implementing arrays of devil's vortex lenses in a reconfigurable spatial light modulator. A simple design procedure assigns the preferred position and topological charge value to each vortex in the structure, tuning the desired angular momentum. Distributions with charges and momenta of the opposite sign have been experimentally demonstrated. The angular velocity exhibited by the phase distribution around the focal plane has been visualized, showing an excellent agreement with the simulations. The practical limits of the method, with interest for applications involving particle transfer and manipula…