Change In Optical Transmission Research Articles

Active control of all-fibre graphene devices with electrical gating.

Active manipulation of light in optical fibres has been extensively studied with great interest because of its compatibility with diverse fibre-optic systems. While graphene exhibits a strong electro-optic effect originating from its gapless Dirac-fermionic band structure, electric control of all-fibre graphene devices remains still highly challenging. Here we report electrically manipulable in-line graphene devices by integrating graphene-based field effect transistors on a side-polished fibre. Ion liquid used in the present work critically acts both as an efficient gating medium with wide electrochemical windows and transparent over-cladding facilitating light–matter interaction. Combined study of unique features in gate-variable electrical transport and optical transition at monolayer and randomly stacked multilayer graphene reveals that the device exhibits significant optical transmission change (>90%) with high efficiency-loss figure of merit. This subsequently modifies nonlinear saturable absorption characteristics of the device, enabling electrically tunable fibre laser at various operational regimes. The proposed device will open promising way for actively controlled optoelectronic and nonlinear photonic devices in all-fibre platform with greatly enhanced graphene–light interaction.

Effects of different post-treatment methods on optical properties, absorption and nanosecond laser-induced damage threshold of Ta2O5 films

Ta2O5 films deposited by ion beam sputtering were post-treated with different methods. The optical properties, microstructures, surface morphologies, absorption and laser-induced damage threshold (LIDT) at 1064nm and 12ns of the films were comparatively studied. Annealing conduced to larger changes of optical transmittance and surface morphologies whereas it led to smaller changes of absorption and LIDT than laser conditioning. As it was shown, all the three post-treatment methods in this study were beneficial to the laser damage resistance of the films, yet the details of the defect elimination caused by these methods were different. A defect evolution model was proposed, which revealed the different effects of post-treatment methods on the defect repair of the films. The highest LIDT achieved by the combination of annealing and laser conditioning was due to their complementary effect which resulted in the lowest defect density and the smallest defect size of the film.

Simultaneous multiselective spectroelectrochemical fiber-optic sensor: demonstration of the concept using methylene blue and ferrocyanide.

Herein, we present a novel spectroelectrochemical fiber-optic sensor that combines electrochemistry, spectroscopy, and electrostatic adsorption in three modes of selectivity. The proposed sensor is simple and consists of a gold mesh cover on a multimode fiber optic that uses attenuated total reflection as the optical detection mode. The sensing is based on changes in the attenuation of the light that passes through the fiber-optic core accompanying the electrochemical oxidation-reduction of an analyte at the electrode. Methylene blue and ferrocyanide were used as model analytes to evaluate the performance of the proposed sensor. The optical transmission changes generated by electrochemical manipulation showed a good linear relationship with the concentration and the limits of detection (3σ) for methylene blue and ferrocyanide at 2.0 × 10(-7) and 1.6 × 10(-3) M, respectively. The sensor responses were successfully enhanced with an additional level of selectivity via an electrostatically adsorbed, self-assembled monolayer (SAM), which consisted of a silane coupling layer, a polyanion, and a polycation. The improvement observed in the sensitivity of a SAM-modified fiber-optic sensor was rather encouraging. The optimized sensor had detection limits (3σ) of 8.3 × 10(-9) M for methylene blue and 7.1 × 10(-4) M for ferrocyanide. The developed sensor was successfully applied to the detection of ferrocyanide in simulated nuclear waste.

Highly efficient arrival timing diagnostics for femtosecond X-ray and optical laser pulses

We developed a diagnostic system for measuring the arrival timing between femtosecond X-ray free-electron laser (XFEL) and near-infrared laser pulses with high efficiency. The ultrafast change in optical transmittance induced by intense XFEL light was probed by a spatial decoding technique. For enhancing detection efficiency, we utilized an X-ray elliptical mirror that increases X-ray intensity by forming a line-focused profile. We found that the system is applicable to the timing diagnostics for 12 keV X-ray pulses with a pulse energy as small as 12 µJ.

Visual detection of methanol in alcoholic beverages using alcohol-responsive poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide) copolymers as indicators

A simple and visual method for quantitative detection of methanol in alcoholic beverages by using alcohol-responsive poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide) (poly(NIPAM-co-DMAA)) linear copolymers as indicators is developed in this paper. The different number of carbon atoms in the alcohol molecules leads to the differential alcohol-responsive characteristics of the poly(NIPAM-co-DMAA) linear copolymer. With replacement of ethanol with an equal volume of methanol in alcoholic solutions, the poly(NIPAM-co-DMAA) copolymer chains change from the shrinking state to the stretching state isothermally. Therefore, the methanol concentration can be simply detected by observing the optical transmittance change of alcoholic beverages with poly(NIPAM-co-DMAA) linear copolymer as an indicator. The minimum methanol concentration that can be visually detected by using the poly(NIPAM-co-DMAA) linear copolymer containing 12.4 mol% of N,N-dimethylacrylamide is as low as 2.5 vol%. The presented detection method with the poly(NIPAM-co-DMAA) linear copolymer as indicator is quite simple and low-cost, and it is valuable for further design of simple and portable tools for home testing the general population, especially in developing countries.

Seeing is believing: hot electron based gold nanoplasmonic optical hydrogen sensor.

We report on the rapid optical detection of gaseous hydrogen using hot electrons generated from resonantly excited substrate-based gold nanohemispheres (Au NHs). We consider hot electron induced H2 dissociation and the subsequent formation of a metastable gold hydride (AuHx) to account for changes in optical transmission. The excitation wavelength was varied to demonstrate a maximum response at the localized surface plasmon resonance (LSPR) wavelength of the AuNHs. Numerical simulations, using the discrete dipole approximation, were employed to corroborate the optical changes associated with the formation of metastable AuHx. Finite time difference domain (FDTD) calculations were also performed to account for the enhanced photocatalytic activity arising due to the confinement of electric fields by the Au NHs. FDTD simulations show that the excitation of the Au NHs plasmon modes generates stronger electric fields at the interface in comparison to a spherical geometry of similar dimensions.

Investigations of reversible optical transmission in gasochromic (Ti–V–Ta)Ox thin film for gas sensing applications

Principle of operation of most gas sensing devices relies on detection of changes of electrical signal upon presence of specified gas. In this work, the changes in optical properties of thin films based on mixtures of selected transition metal oxides under ethanol vapor have been outlined. The test thin films were prepared by reactive magnetron sputtering from mosaic target containing Ti, V, and Ta. Gas sensing properties were investigated through observations of the change in optical transmission. Dynamic optical response recorded in proposed optical gas sensing system shows relatively fast sample response/recovery times under different air/ethanol vapor environment. All measurements were collected at room temperature and no additional catalyst was used to activate sample dimming. Based on performed measurements construction of a simple optical detection system of ethanol vapor was proposed and tested.

New triphenylamine-based poly(amine-imide)s with carbazole-substituents for electrochromic applications

A new carbazole-derived triphenylamine-containing diimide-diacid monomer (5), 4,4′-bis(trimellitimido)-4″-N-carbazolytriphenylamine, is prepared by the condensation of 4,4′-diamino-4″-N-carbazolytriphenylamine (4) and two molar equivalents of trimellitic anhydride (TMA). A series of new poly(amide-imide)s (PAIs) 7a–7d with carbazole-substituted triphenylamine units are prepared by direct polymerization from the new diimide-diacid (5) and various aromatic diamines (6a–6d). The PAIs shows high glass transition temperature between 269 and 297°C, and high 5% weight loss temperature between 526 and 561°C under nitrogen environment. Cyclic voltammograms of the PAIs films, which are casted onto the indium–tin oxide (ITO)-coated glass substrate, exhibit two reversible oxidation redox couples at 1.05–1.08V and 1.38–1.46V under an anodic sweep. The PAI-7a film reveals excellent stability of electrochromic characteristics for the radical cations generated, changing color from original pale yellowish neutral form to the green and then to dark blue oxidized forms. Furthermore, the anodically coloring of PAI-7a shows high coloration efficiency (CE=205cm2/C), high contrast of optical transmittance change (ΔT=80% at 776nm) and long-term redox reversibility.

Results on damage induced by high-energy protons in LYSO calorimeter crystals

Lutetium-Yttrium Orthosilicate doped with Cerium (LYSO), as a bright scintillating crystal, is a candidate for calorimetry applications in strong ionising-radiation fields and large high-energy hadron fluences are expected at the CERN Large Hadron Collider after the planned High-Luminosity upgrade. There, proton–proton collisions will produce fast hadron fluences up to ~5×1014cm−2 in the large-rapidity regions of the calorimeters.The performance of LYSO has been investigated, after exposure to different fluences of 24GeVc−1 protons. Measured changes in optical transmission as a function of proton fluence are presented, and the evolution over time due to spontaneous recovery at room temperature is studied.The activation of materials will also be an issue in the described environment. Studies of the ambient dose induced by LYSO and its evolution with time, in comparison with other scintillating crystals, have also been performed through measurements and FLUKA simulations.

Preparation, Characterization of Styrene-Functional Hyperbranched Viologen, and Its Application in Optical Writing and Electrical Erasing Device

Styrene-functional hyperbranched viologen (SHBV2+) was successfully synthesized and characterized in detail by FTIR, 1H NMR, and XPS spectra, respectively. Subsequently, it was cured by visible light to obtain cross-linked hyperbranched viologen film. It is noteworthy that cross-linked SHBV2+ film possessed better photochromic and electrochromic performances. After UV illumination for 60 s, the cross-linked SHBV2+ film can swiftly change its color from pale yellow to deep bluish violet, whereas the absorbance of SHBV2+ film at 610 nm did not change significantly and was still retained about 0.423 after 20 coloring/bleaching cycles. The single-type SHBV2+ EC device can undergo reversible color change in response to the alternate external voltages of −2.0 V and 2.0 V, respectively, while the changes in optical transmission and charge density of EC device at 550 nm did not deteriorate significantly and still remained about 48.2% and 13.85 mC·cm−2 after 10 coloring/bleaching cycles. Furthermore, single-type SHBV2+ PEC device possessed better optical writing and electrical erasing performances. After 10 repeated writing/erasing cycles, the contrast did not decrease significantly and still remained about 48.0%, while the electrical erasing time did not deteriorate significantly and remained about 22.0 s. This device can realize rapid storage, modulation, and erasing of optical information.

Two New Near-Infrared Switchable Electrochromic Bithiophenes Derivatives Based on 4-Methoxytriphenylamine Unit and Their Application for Electrochromic Devices

Two novel triphenylamine-containing thiophene derivative monomers, 4-methoxy-4′,4″-di(thiophen-2-yl)triphenylamine (MTTPA) and 4-methoxy-4′,4″-di(2,3-dihydrothieno[3,4-b][1,4]dioxin-7-yl)triphenylamine (METPA), were successfully synthesized. The corresponding polymers including PMTTPA and PMETPA were electrochemically synthesized and characterized by cyclic voltammetry (CV), UV–vis–NIR spectroscopy and scanning electron microscopy (SEM). Electrochemical and spectroelectrochemical analysis showed that two polymers had reversible redox behavior and multi-electrochromic property. Dynamic electrochromic experiments suggested that both the polymers had rapid switching time, high coloration efficiency, and high contrast of optical transmittance changes (ΔT%) in the NIR region (55.5% at 1280 nm for PMTTPA, 77.6% at 1200 nm for PMETPA). The dual-type electrochromic device based on PMTTPA film (or PMETPA film) was constructed and characterized as well. Both of them revealed excellent properties.

Heat resistant polymer electrolyte for enhanced organic electrochromic windows based on poly (3,3-dimethyl-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepine)

ABSTRACTElectrochromic Windows(ECWs) have the potential to save energy through dynamic control of light and solar energy entering a room (via solar heat gain coefficient control). ECWs have been developed as an optical shutter in airplane, building and automobile applications. An ECW is composed of three components, a working electrode based on electrochromic materials, a counter electrode based on ion storage materials and the electrolyte as an ionic conducting layer. Organic ECWs have been gaining popularity due to easy and cost effective manufacturing, availability of wide range of colors, high optical contrast and flexibility in design. However there are challenges in commercialization and application of organic ECWs. The application of ECWs as a sunroof in automobiles demands operation in harsh environment conditions like elevated temperature. Consequently the University of Washington, Center for Intelligent Materials and Systems has been developing a heat resistant organic ECW that can be operated at elevated temperatures maintaining high optical contrast, fast switching speed, optical color memory and electrochemical stability. The proposed design is an ECW based on poly (3,3-dimethyl-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepine),PPRODOT-Me2 as a working electrode, V2O5-TiO2 composite materials as a counter electrode and poly(ethylene imine) based electrolyte. The ionic conductivity of the electrolyte was calculated through complex impedance method and temperature dependence of the electrolyte was determined using environment test chamber to control a temperature range of 15 to 80o Celsius for 100 hours. A 76 × 76 mm2 ECW was developed and the optical transmittance change was observed by Chronoamperomerty and Time course measurement. The electrochemical stability of the window was monitored using cyclic voltammetry. The developed electrochromic window showed good optical contrast, electrochemical stability and fast response time after testing at elevated temperatures for 100 hours.

Electrochromic Device Containing Heptyl Viologen, PEDOT, TiO2 and TEMPO

An electrochromic device containing heptyl viologen, poly(3,4-ethylenedioxythiophene) (PEDOT), TiO2 and 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) was fabricated. Both heptyl viologen and PEDOT are electrochromic materials with different spectra at its colored states. The transmission spectrum was measured in different voltages in a wide wavelength range from near infrared to near ultraviolet. By combining PEDOT and heptyl viologen, a high on/off contrast was obtained with almost zero transmittance in a dark state. Also, the TiO2 layer increased optical transmittance change, as it provides a large surface area where the heptyl viologen was reduced to be colored. On the other hand, the TiO2 layer did not decrease the on/off switching time.

An electrodeless quartz crystal resonator integrated with UV/Vis spectroscopy for the investigation of the photodecomposition of methylene blue

The photodecomposition of organic molecules (methylene blue) was investigated using an integrated system consisting of a UV–vis spectrometer and an electrodeless quartz crystal microbalance (EL-QCM). ZnO nanorods were directly grown on a bare quartz crystal and methylene blue was coated onto the nanorods by drop-casting. Ring-type remote electrodes were used to enable the transmission of light. As the coated methylene blue was photo decomposed by UV light, the changes in mass and light transmittance were measured with the EL-QCM and UV–vis spectrometer respectively. These simultaneous measurements revealed that the rate of change in optical transmission is greater than that of the mass in the early stage of photodecomposition, which indicates that the structural degradation of methylene blue is dominant in the early stage. In contrast, the changes in light transmittance were linearly proportional to those in mass during the later stages, which is attributed to the mineralization of methylene blue.

Jet impingement heat transfer using a Field’s alloy nanoparticle – HFE7100 slurry

An experimental study was performed to investigate jet impingement heat transfer of HFE7100 dielectric liquid with metallic phase change materials (Field’s alloy) in nanometer particulate form (nano PCM). A simple method was used to prevent the precipitation of Field’s alloy nanoparticles in a HFE7100 suspension by surface modification with silane monolayers. The optical transmittance of the nanoparticle suspension was monitored by a portable spectrometer and there was no significant change in optical transmittance over time. The nano PCM particle suspension impinges on a heated surface and absorbs heat by phase change process from solid to liquid phase coupled with the evaporation of HFE7100. The present study shows that the mass fraction of nanoparticles plays an insignificant role in pressure drop but an important role on heat transfer performance. The high-heat-flux removal capability has been demonstrated by repeated closed loop test. Our results show that slurries with 30% particle mass fraction can improve the average heat transfer coefficient by 70% when compared to pure HFE7100 in the temperature range of 62–66°C.

The influence of oxygen on the microstructural, optical and photochromic properties of polymer-matrix, tungsten-oxide nanocomposite films

An in situ vapor deposition process has been used to create a photochromic, tungsten-oxide, polymer matrix nanocomposite. Under specific processing conditions, the composite consists of discrete tungsten-oxide nanoparticles distributed uniformly throughout the bulk of an optically transparent fluoropolymer matrix. Ultraviolet exposure of the nanocomposite produces characteristic photochromic changes that result in a 40% change in optical transmission. Optical absorption measurements yield a value of 3.08eV for the bandgap of the tungsten-oxide particles. Incorporating oxygen as a supplementary deposition agent in the synthesis process increased the transparency of the films in the visible region, increased the change in transmission due to the photochromic effect, and led to the percolation of larger nanoparticles near the film surface. Growth of particles in this region allowed the nanocomposite to be bleached readily in an oxygen atmosphere while retaining photochromic activity.

Composite for smarter windows

Glass has been prepared that selectively absorbs visible and near-infrared light when an electrochemical voltage is applied. This opens the way to 'smart' windows that block heat on demand, with or without optical transparency. See Letter p.323 Glass windows let in light and keep out extreme heat and cold, but with the advance of the field of electrochromism — the reversible change of optical transmittance in response to electrochemical charge and discharge — they could do much more. Delia Milliron and co-workers have made a step towards producing windows that can greatly reduce lighting and heating costs with the demonstration of a composite film composed of tin-doped indium oxide nanocrystals embedded in a niobium oxide glass matrix. By varying an applied voltage over a 2.5-volt range, the charged nanocrystals selectively block near-infrared light, while the glass strongly modulates visible light owing to its reconstructed bonding near the nanocrystal–glass interface. Practical 'smart windows' and other devices are still some way off, but this solution-processed nanocrystal-in-glass approach is modular and permits extensive tuning of structure and composition, and so provides a solid platform for further refinement.

Surface stress sensor using MEMS-based Fabry–Perot interferometer for label-free biosensing

We have recently developed a surface stress sensor based on a microelectromechanical system Fabry–Perot interferometer integrated with a photodiode, which utilizes the nonlinear optical transmittance change in the Fabry–Perot interference to enhance the sensitivity of the surface stress. The novel signal transducing technique from the surface stress caused by molecular adsorption to the electrical readout is carried out in three steps, namely, mechanical deflection, transmittance change, and photocurrent change. Parylene-C was used as a deformable membrane in the sensor because of its high optical transmittance, low Young's modulus, and negligible residual stress, which provides a flat freestanding membrane. The theoretical minimum detectable surface stress of the proposed sensor was predicted to be −1μN/m, which is two orders of magnitude greater than that of the piezoresistor-embedded surface stress sensor. The Fabry–Perot surface stress sensor was fabricated using a semiconductor fabrication process and sacrificial release process. An encapsulating structure for the Fabry–Perot cavity that uses a dry film resist by a roll-to-roll technique enabled us to use wet condition for detection of biomolecules. Amino-methyl-functionalized parylene was coated on the parylene-C membrane for immobilization of the biomolecules via electrostatic coupling between biomolecules and the amino group. The photocurrent was demonstrated to shift by 23.7nA at a 3-V reverse bias voltage with immobilized antibodies. This Fabry–Perot sensor allows the use of a universal biochemical sensing platform in a label-free manner.

Thermal oxidation-grown vanadium dioxide thin films on FTO (Fluorine-doped tin oxide) substrates

By deposition of metallic vanadium on FTO substrate in Argon atmosphere at room temperature, the sample was then annealed in furnace for 2h at the temperature of 410°C in air ambient. (110) -orientated vanadium dioxide films were prepared on the FTO surface. A maximum transmittance of ∼40% happened at 900–1250nm region at room temperature. The change of optical transmittance at this region was ∼25% between semiconducting and metallic states. In particular, vanadium dioxide thin films on FTO exhibit semiconductor–metal phase transition at ∼51°C, the width of the hysteresis loop is ∼8°C.

Portable Diagnosis Method of Hyperkalemia Using Potassium-Recognizable Poly(N-isopropylacrylamide-co-benzo-15-crown-5-acrylamide) Copolymers

A novel, simple, portable, and low-cost method for diagnosis of hyperkalemia by using K(+)-recognizable poly(N-isopropylacrylamide-co-benzo-15-crown-5-acrylamide) [poly(NIPAM-co-B15C5Am)] linear copolymer as indicator is presented in this work. The pendent 15-crown-5 units in the linear copolymers can selectively and specifically recognize K(+) to form stable 2:1 "sandwich" host-guest complexes, which cause the copolymer chains to change from the hydrophilic state to the hydrophobic state isothermally, whereas other tested metal ions (e.g., Li(+), Na(+), Cs(+), Mg(2+), Ca(2+), Sr(2+), Ba(2+), Cu(2+), Fe(3+), Pb(2+), Cd(2+), Cr(3+)) cannot be recognized. With increasing the 15-crown-5 content or the K(+) concentration, the poly(NIPAM-co-B15C5Am) linear copolymers exhibit higher sensitivity to K(+). The hyperkalemia can be simply diagnosed by observing the K(+)-induced optical transmittance change of human blood samples with poly(NIPAM-co-B15C5Am) linear copolymer as an indicator. Normal blood samples with low potassium level containing the poly(NIPAM-co-B15C5Am) linear copolymer are almost transparent since the copolymer is hydrophilic and soluble at the operating temperature. However, severe hyperkalemia samples with high potassium level become completely cloudy since the copolymer is hydrophobic and insoluble at this temperature. The presented diagnosis method with poly(NIPAM-co-B15C5Am) linear copolymer as indicator is quite simple and low-cost, and it would bring a new candidate material to design simple and portable tools for diagnosis of hyperkalemia in the general population. Moreover, the results in this work provide valuable guidance for building novel poly(NIPAM-co-B15C5Am)-based artificial K(+)-recognizable "smart" or "intelligent" systems in various application fields.