Search results for "Efficient"
showing 10 items of 1603 documents
Second-harmonic generation in Langmuir–Blodgett monolayers of stilbazium salt and phenylhydrazone dyes
1988
The second-order nonlinear optical susceptibilities χ(2) of several phenylhydrazone and stilbazium salt dyes in Langmuir–Blodgett monolayers have been determined from second-harmonic-generation measurements. Three of the substances demonstrated χ(2) values greater than 10−6 electrostatic units, although two of the three did not absorb light significantly at the second-harmonic wavelength.
Near-Field Distribution of Optical Transmission of Periodic Subwavelength Holes in a Metal Film
2000
Recent experimental discovery of the enhanced optical transmission through metal films with periodic subwavelength holes has given rise to a considerable interest in the optical properties of such structures due to their possible numerous applications in optics and optoelectronics as well as rich physics behind the phenomenon of the transmission enhancement [1–4]. The transmission of a subwavelength aperture is very low and proportional to the fourth power of the ratio of its diameter and light wavelength. However, if a metal film is perforated with a periodic array of such holes, the optical transmission can be significantly enhanced [1]. Being normalized to the total area of the illuminat…
Broadband microwave gas sensor: A coaxial design
2010
The method of gas detection by a broadband microwave gas sensor is presented in this article. The principle of this method is to use a sensitive material as substrate of a transmission coaxial line. The sensor represents an open line with an extreme surface in contact with gas. The interaction with the gas and the surface induces a dielectric variation of the substrate. From experimental results, the interaction between the sensitive material and each tested gas present a specific frequency spectrum of the reflection coefficient at the input of the line. The proposed method has the advantage of a compact size, wide bandwidth, simple structure, and capable with all sensitive materials. © 201…
Using crystallographic shear to reduce lattice thermal conductivity: high temperature thermoelectric characterization of the spark plasma sintered Ma…
2013
Engineering of nanoscale structures is a requisite for controlling the electrical and thermal transport in solids, in particular for thermoelectric applications that require a conflicting combination of low thermal conductivity and low electrical resistivity. We report the thermoelectric properties of spark plasma sintered Magnéli phases WO2.90 and WO2.722. The crystallographic shear planes, which are a typical feature of the crystal structures of Magnéli-type metal oxides, lead to a remarkably low thermal conductivity for WO2.90. The figures of merit (ZT = 0.13 at 1100 K for WO2.90 and 0.07 at 1100 K for WO2.722) are relatively high for tungsten-oxygen compounds and metal oxides in general…
Optical tuning of dielectric nanoantennas for thermo-optically reconfigurable nonlinear metasurfaces
2021
We demonstrate optically tunable control of second-harmonic generation in all-dielectric nanoantennas: by using a control beam that is absorbed by the nanoresonator, we thermo-optically change the refractive index of the radiating element to modulate the amplitude of the second-harmonic signal. For a moderate temperature increase of roughly 40 K, modulation of the efficiency up to 60% is demonstrated; this large tunability of the single meta-atom response paves the way to exciting avenues for reconfigurable homogeneous and heterogeneous metasurfaces.
Spatially resolved optical studies of F-center diffusion in KBr crystals.
1996
Spatially resolved optical studies of F-center diffusion during and after the photothermal F\ensuremath{\rightarrow}X color center conversion have been performed by optical scanning and holographic methods in electrolytically colored KBr crystals. Average velocities and diffusion coefficients of F centers have been determined for Gaussian and periodical spatial exposing light intensity distributions. A strong influence of the light intensity gradient has been found on F-center diffusion. It manifests itself by a rapid increase of the effective diffusion coefficient when the light intensity gradient is decreased. This behavior allowed us to explain the observed peculiarities of the holograph…
Performance increase of membrane distillation pilot scale modules operating in vacuum-enhanced air-gap configuration
2019
Abstract This paper presents the first experimental evaluation at pilot scale of the operation of vacuum-enhanced air-gap membrane distillation (V-AGMD) using two commercial spiral-wound modules at Plataforma Solar de Almeria's solar desalination test facilities. The main difference between the modules was the channel length (1.5 and 2.7 m) as a result of having different membrane surface area (7.2 m2 and 25.9 m2 respectively) and different number of envelopes. Suction of air from the gap improved the vapour transfer through the membrane pores and the performance of the modules was significantly increased in relation to common air-gap (AGMD) operational mode, especially in the treatment of …
Raman spectra of (PbS)1.18(TiS2)2 misfit compound
2007
Abstract A Raman study on the (PbS)1.18(TiS2)2 semiconductor structure with incommensurate layers (misfit) is reported. The different bands observed in the spectra are attributed to both the TiS2 host layers, at 219 (Eg) and 333 (A1g) cm−1, and the intercalated PbS layers: the LO(Γ), 2LO and 3LO phonons at 203, 412 and 634 cm−1, respectively. A phonon peak probably related to the superposition of TiS2 and PbS vibrations, was observed near 286 cm−1. The decrease of the phonon wave numbers (of the modes located at 203, 333, 412, and 634 cm−1) with increasing laser power pointed out negative temperature coefficients of these modes. A peak appearing with laser power near 151 cm−1 is discussed. …
Manufacturing Te/PEDOT Films for Thermoelectric Applications
2017
In this work, flexible Te films have been synthesized by electrochemical deposition using PEDOT [poly(3,4-ethylenedioxythiophene)] nanofilms as working electrodes. The Te electrodeposition time was varied to find the best thermoelectric properties of the Te/PEDOT double layers. To show the high quality of the Te films grown on PEDOT, the samples were analyzed by Raman spectroscopy, showing the three Raman active modes of Te: E1, A1, and E2. The X-ray diffraction spectra also confirmed the presence of crystalline Te on top of the PEDOT films. The morphology of the Te/PEDOT films was studied using scanning electron microscopy, showing a homogeneous distribution of Te along the film. Also an a…
Improving the vertical radiation pattern issued from multiple nano-groove scattering centers acting as an antenna for future integrated optics Fourie…
2019
The stationary wave integrated Fourier transform spectrometer (SWIFTS) is based on the sampling of a stationary wave using nano-scattering centers on the surface of a channel waveguide. Single nano-scale scattering centers above the waveguide surface will radiate the sampled signal with wide angular distribution, which is not compatible with the buried detection area of infrared (IR) detectors, resulting in crosstalk between pixels. An implementation of multiple diffraction nano-grooves (antenna) for each sampling center is proposed as an alternative solution to improve directivity towards the detector pixel by narrowing the scattering angle of the extracted light. Its efficiency is demonst…