Spectral Transmittance Measurements Research Articles

LSPR enhanced MSM UV photodetectors

We fabricated localized surface plasmon resonance enhanced UV photodetectors on MOCVD grown semi-insulating GaN. Plasmonic resonance in the UV region was attained using 36 nm diameter Al nanoparticles. Extinction spectra of the nanoparticles were measured through spectral transmission measurements. A resonant extinction peak around 300 nm was obtained with Al nanoparticles. These particles gave rise to enhanced absorption in GaN at 340 nm. Spectral responsivity measurements revealed an enhancement factor of 1.5. These results provided experimental verification for obtaining field enhancement by using Al nanoparticles on GaN.

Human tissue color as viewed in high dynamic range optical spectral transmission measurements

High dynamic range optical-to-near-infrared transmission measurements for different parts of human body in the spectral range from 650 to 950 nm have been performed. Experimentally measured spectra are correlated with Monte Carlo simulations using chromaticity coordinates in CIE 1976 L*a*b* color space. Both a qualitative and a quantitative agreement have been found, paving a new way of characterizing human tissues in vivo. The newly developed experimental and computational platform for assessing tissue transmission spectra is anticipated to have a considerable impact on identifying favorable conditions for laser surgery and optical diagnostics, while providing supplementary information about tissue properties.

Potential of optical spectral transmission measurements for joint inflammation measurements in rheumatoid arthritis patients

Frequent monitoring of rheumatoid arthritis (RA) patients enables timely treatment adjustments and improved outcomes. Currently this is not feasible due to a shortage of rheumatologists. An optical spectral transmission device is presented for objective assessment of joint inflammation in RA patients, while improving diagnostic accuracy and clinical workflow. A cross-sectional, nonrandomized observational study was performed with this device. In the study, 77 proximal interphalangeal (PIP) joints in 67 patients have been analyzed. Inflammation of these PIP joints was also assessed by a rheumatologist with a score varying from 1 (not inflamed) to 5 (severely inflamed). Out of 77 measurements, 27 were performed in moderate to strongly inflamed PIP joints. Comparison between the clinical assessment and an optical measurement showed a correlation coefficient r=0.63, p<0.001, 95% CI [0.47, 0.75], and a ROC curve (AUC=0.88) that shows a relative good specificity and sensitivity. Optical spectral transmission measurements in a single joint correlate with clinical assessment of joint inflammation, and therefore might be useful in monitoring joint inflammation in RA patients.

Caractérisation radiative de liquides volatils semi-transparents dans le domaine infrarouge

The LNE has developed a technique to measure infrared radiative properties of volatile liquids. LNE uses a homemade reflectometer for the measurement of the spectral directional hemispherical reflectance from 0.8 μm to 14 μm and a Fourier transform spectrometer for the measurement of the regular spectral transmittance from 1 μm to 25 μm. For volatile liquids, a tight cell with two infrared windows was constructed. Optical models were developed to calculate the spectral complex refractive index of the liquid from reflectance and transmittance results. Results were validated for water by comparison to data found in literature.

3D nanoimprinted Fabry–Pérot filter arrays and methodologies for optical characterization

Fabry–Perot (FP) filter arrays fabricated by high-resolution three dimensional (3D) NanoImprint technology are presented. A fabrication process to implement 3D templates with very high vertical resolution is developed. Filter arrays with 64 different cavity heights have been fabricated requiring only one single imprint step. Different optical methods are involved in this paper to characterize geometric and spectral properties. In order to investigate the transfer accuracy of the surface quality from the NanoImprint template to the filter, we use white light interferometry (WLI) measurements. Surface roughness and structure height accuracy of <1 nm for both values demonstrate the conservation of these critical parameters during the 3D NanoImprint process. Additionally, an optical characterization methodology for spectral transmission and reflection measurements of the filter arrays is introduced and applied. A compact microscope spectrometer setup which allows efficient handling, high resolution and short inspection time is verified by comparing measurement results to that of an optical bench setup used as a reference. First, this paper focuses on the foundation of the FP filter arrays, second on the technological fabrication, third on validation calibration of the setup and forth on the characterization of the filter arrays. The measurements envisage the spectral position of filter transmission lines, the full width at half maximum (FWHM) and the total spectral bandwidth of the array, i.e. the stopbands of the included Distributed Bragg Reflectors (DBRs).

Study of crystallization process of Eu doped SrGa2S4 thin film phosphors by two electron beams evaporation and 355 nm Nd:YAG laser-annealing

In this study, the detailed crystallization mechanism of SrGa2S4: Eu2+ thin film phosphors annealed by Nd:YAG laser (355nm) was examined. Using the spectral transmittance measurements of SrS and Ga2S3 thin films, the influence of temperature on SrGa2S4 thin film formation by laser irradiation was investigated using the thermal conducting equation. From the calculation, it is thought that Ga2S3 absorbed greater laser energy than SrS and generated the heat. By diffusing heat throughout the thin film, crystallization was promoted.

Raman scattering characterization of ZnSe/Zn0.6Cd0.4Se multilayers prepared by thermal vacuum evaporation

AbstractNanocrystalline multilayers from ZnSe/Zn0.6Cd0.4Se with three different layer thicknesses (3.5, 5.0, 10.0 nm) and, for comparison, 400 nm thick Zn0.6Cd0.4Se nanocrystalline single layers have been prepared by thermal evaporation of ZnSe and CdSe in vacuum. Raman scattering spectra have been measured in the range 100–1000 cm−1 under excitation with the 488 and 514.5 nm lines of an Ar+ laser. Series of four bands have been seen in the spectra of all samples. They have been related to replicas of the longitudinal optical LO‐phonon in the ZnxCd1−xSe layers and interpreted as an indication for crystallinity of both kinds of samples. A blue shift of the 1 LO maximum has been observed, which has been connected with an increase of the compressive stress in the ternary layers when the layer thickness decreases. It has also been obtained that the ratio of the integrated intensity of the 1 LO band in the spectra taken with the 488 and 514.5 nm lines decreases with decreasing Zn0.6Cd0.4Se layer thickness. The result has been assigned to size‐induced increase of the optical band gap of the layers. This conclusion has been confirmed by spectral photocurrent and optical transmission measurements.

Morphology and Optical Measurements of Nanostructured In&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O&amp;lt;sub&amp;gt;3&amp;lt;/sub&amp;gt;:SnO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; Nanoparticle

Ultra-fine and uniform ITO nanopowders can be prepared by very simple Combustion method. In this paper, effects of Indium oxide with Sn doping on crystallinity, band gap values by UV studies and morphological studies by SEM and TEM analysis of nanopowders are reported. Powder mixtures of In2O3:SnO2 of 90:10 compositions are prepared and calculated grain size from X-ray diffraction measurements. The free electron absorption is determined from spectral transmission and reflection measurements. Key words: In2O3:SnO2, XRD, UV, Combustion and SEM.

Experimental Determination of Transmittance of Porous Cerium Dioxide Media in the Spectral Range of 300–1,100 nm

A spectroscopy system is developed to measure radiative characteristics of participating media in the spectral range of 300–1,100 nm. The system incorporates a short-arc radiation source, double monochromator, optical chopper synchronized with a lock-in amplifier, and a silicon detector. Measurements of overall spectral transmittance are performed with two types of cerium dioxide samples with average porosities of 0.08 and 0.72, respectively. For both sample types, the spectral variation of the transmittance indicates mixed contribution by absorption and scattering to the observed attenuation in the considered spectral range. All samples are characterized by high opacity to radiation up to approximately 400 nm.

Doped, porous iron oxide films and their optical functions and anodic photocurrents for solar water splitting

The fabrication and morphological, optical, and photoelectrochemical characterization of doped iron oxide films is presented. The complex index of refraction and absorption coefficient of polycrystalline films are determined through measurement and modeling of spectral transmission and reflection data using appropriate dispersion relations. Photoelectrochemical characterization for water photo-oxidation reveals that the conversion efficiencies of electrodes are strongly influenced by substrate temperature during their oblique-angle physical vapor deposition. These results are discussed in terms of the films’ morphological features and the known optoelectronic limitations of iron oxide films for application in solar water splitting devices.

Study on micro-crystallization, growth, optical properties and defects of a nonlinear optical crystal: MnHg(SCN) 4

High optical quality single crystals of a nonlinear optical material, manganese mercury thiocyanate, MnHg(SCN) 4 (MMTC), with dimensions up to 21×14×13 mm 3 have been grown by the solvent evaporation method. The growth habit of MMTC crystal crystallized under different conditions was investigated by means of micro-crystallization method. Two typical growth morphologies of the crystal were indexed and compared with the morphology deduced from the single crystal structure data. The results show that two novel {1 0 0} and {1 1 2} facets appear during the crystal growth. Powder second harmonic generation and spectral transmittance measurements were also performed. The results indicate that MMTC is phase-matchable and the UV transparency cutoff occurs at 373 nm. Various defects were found in MMTC crystal. Their formation mechanisms and the methods to eliminate these defects are discussed.

Au thin films deposited on SnO2:In and glass: Substrate effects on the optical and electrical properties

We report on a detailed study on the optical and electrical properties of Au films made by sputter deposition onto glass substrates with and without transparent and electrically conducting layers of SnO2:In. The Au films had thicknesses up to 10.7nm and hence spanned the range for thin film growth from discrete islands, via large scale coalescence and formation of a meandering conducting network, to the formation of a more or less “holey” film. Scanning electron microscopy and atomic force microscopy demonstrated that the SnO2:In films were considerably rougher than the glass itself, and this roughness influenced the Au film formation so that large scale coalescence set in at a somewhat larger thickness for films on SnO2:In than on glass. Measurements of spectral optical transmittance and reflectance and of electrical resistance gave a fully consistent picture that could be reconciled with impeded Au film formation on the SnO2:In layer; this led to pronounced “plateaus” in the near infrared optical spectra for Au films on SnO2:In and a concomitant change from such two-layer films having a lower resistance than the single gold film at thicknesses below large scale coalescence to the opposite behavior for larger film thicknesses. Our work highlights the importance of the substrate roughness for transparent conductors comprising coinage metal films backed by wide band gap transparent conducting oxides.

Spectral characterization of porous dielectric subwavelength THz fibers fabricated using a microstructured molding technique

We report two novel fabrication techniques, as well as THz spectral transmission and propagation loss measurements of subwavelength plastic wires with highly porous (up to 86%) and non-porous transverse geometries. The two fabrication techniques we describe are based on the microstructured molding approach. In one technique the mold is made completely from silica by stacking and fusing silica capillaries to the bottom of a silica ampoule. The melted material is then poured into the silica mold to cast the microstructured preform. Another approach uses a microstructured mold made of a sacrificial plastic which is co-drawn with a cast preform. Material from the sacrificial mold is then dissolved after fi ber drawing. We also describe a novel THz-TDS setup with an easily adjustable optical path length, designed to perform cutback measurements using THz fibers of up to 50 cm in length. We fi nd that while both porous and non-porous subwavelength fibers of the same outside diameter have low propagation losses (alpha <or= 0.02 cm(-1)), the porous fi bers exhibit a much wider spectral transmission window and enable transmission at higher frequencies compared to the non-porous fibers. We then show that the typical bell-shaped transmission spectra of the subwavelengths fibers can be very well explained by the onset of material absorption loss at higher frequencies, due to strong confinement of the modal fields in the material region of the fi ber, as well as strong coupling loss at lower frequencies, due to mismatch between the modal field diameter and the size of the gaussian-like beam of a THz source.

Solar Control Glass

Solar control glass has applications for windows and glazed facades in order to modify indoor visual and thermal comfort in buildings. The article presents the results of evaluation study of optical properties of selected types of solar control glasses and foils. The spectral transmittance measurements were used as input data for daylight comparative studies, and the consideration of convenience of selected solar control glasses and foils for windows are summarised on the basis of analysis of optical properties.

Planning magneto-optical filters for the study of magnetic oscillations of the Sun

VAMOS is a Magneto-Optical Filter (MOF) that can acquire nearly simultaneous Dopplergrams and magnetograms with high cadence in the K I 7699 A line. We performed an accurate set-up of this instrument in view of its use for studying oscillations in solar magnetic regions. The optimal set-up for VAMOS was achieved and an extra result of the spectral transmission measurements was found. The MOF and Wing Selector (WS) bandpasses depend not only on the cell temperature and magnetic field but also on the radiation intensity entering the cell, when this radiation exceeds a suitable level. We call this effect The Intensity Effect.

A modern concept for autonomous and continuous measurements of spectral albedo and transmittance of sea ice

Abstract Time series of irradiance data measured on sea ice with high temporal and spectral resolution are needed for advancing studies of atmosphere–ice–ocean interaction during different seasons. In particular, more observations of under-ice irradiance are needed to quantify fluxes through snow and sea ice and their seasonality, because the vertical and spectral partitioning of solar radiation are still among the biggest unknowns in today's descriptions of sea-ice related processes. Our current understanding of the interaction of radiation and sea ice is based on only a few data sets, yet this interaction is crucial for describing such processes as sea-ice formation, snow metamorphism, and snow and ice melt, as well as biological productivity and abundance. A modern setup for synchronous, autonomous, continuous, and high temporal-resolution measurements of spectral albedo and transmittance of sea ice is presented. The setup is based on three spectral radiometers, covering a wavelength range from 320 to 950 nm with 3.3 nm spectral resolution. Sensors, data logger, and their setup have worked well in several campaigns under challenging climatic conditions. The longest campaign lasted more than 4 months, without the need for maintenance, and the sensors have shown good performance related to surface contamination, one of the most challenging aspects for radiation measurements. Measured data are of high quality, including details of spectral shapes and high sensitivity to changes in observed snow and ice conditions. All spectra are calibrated for absolute readings, allowing applications in a wide variety of snow and ice studies and their comparison. A sample data set, collected over two weeks in the central Arctic, is presented and shows how the vertical partitioning of irradiance changes during the transition from summer to autumn. The main advantage of the system is its suitability for autonomous and long-term observations over and under sea ice. Furthermore, the setup is portable and robust, and can be easily and quickly installed, which is most valuable for deployment under harsh conditions and also encourages short observation periods. Spectral range and other technical features permit the application of this setup for various interdisciplinary studies, too.

Electrical and optical properties of thin films with a SnS2 – Bi2S3 alloy grown by sulphurization

In this work, thin films of SnS2 with increased Bi content were grown by sulphurization of a thin film of Sn:Bi alloy, at temperatures around 300°C. The effect of the Bi concentration on the optical, electrical and structural properties was determined through measurements of spectral transmittance, conductivity and x-ray diffraction XRD respectively. It was found that the optical constants (refractive index n, absorption coefficient α and energy gap Eg) and the electrical conductivity are significantly affected by the Bi concentration. In particular, a variation of the energy gap between 1.44 and 1.63 eV and a change of the conductivity greater than three orders of magnitude were observed when the content of Bi in the Sn:Bi alloy varied between 0 and 100 %. The analysis of the XRD measurements allowed us to find that the SnS: Bi films grow with a mixture of the SnS2 and Bi2S3 phases, independently of the Bi content.

Effect of substrate temperature on the optical, structural and morphological properties of In2Se3 thin films grown by a two-step process

Polycrystalline γ – In2Se3 thin films with adequate properties to use them as buffer layer in solar cells, were grown on corning glass substrates using a novel procedure which includes the formation of the α- In2Se3 phase in a first step followed by thermal annealing in Se ambient to activate the formation of the γ- In2Se3 phase. X-ray diffraction (XRD) measurements revealed that the substrate temperature strongly affects the phase in which the indium selenide films grow; at substrate temperatures of around 300°C the indium selenide grow in the α-In2Se3 phase, whereas the samples deposited at temperatures between 300 and 550°C grow with a mixture of the α-In2Se3 and γ-In2Se3 phases. The α-In2Se3 samples change into the γ-In2Se3 phase when subjected to heat treatment around 550°C in Se ambient. Spectrophotometric measurements also revealed that the phase in which the indium selenide films grow, significantly affects the optical gap Eg. Eg values of 1.47 eV and 2.11 eV were determined for the α-In2Se3 and γ-In2Se3 films respectively, indicating that this γ-In2Se3 compound has better properties to perform as buffer layer in thin film solar cells. The effect of substrate temperature on the structural, optical and morphological properties was investigated using XRD, spectral transmittance and atomic force microscope (AFM) measurements. Theoretical simulation of the XRD pattern carried out with the help of the PowderCell package, allowed us to identify the phases associated to the X-Ray reflections, with a good degree of confidence.

Apparatus for probing preignition behavior of hypergolic materials

The determination of the condensed-phase preignition chemistry of hypergolic bipropellant pairs has been considerably challenging due to toxicity and reactivity of the used materials. In this work, we describe a new experimental technique for characterizing preignition behavior of hypergolic materials. Small quantities of the bipropellant pair are brought in contact under isothermal conditions, and spectral transmission measurements on the evolved products are performed using Fourier transform infrared spectroscopy. The gaseous products are subsequently quantified to yield species concentration profiles at various temperatures, hence facilitating the elucidation of the detailed condensed-phase chemical kinetics responsible for the ignition in the gas phase.

A hydrographic time series station in the Wadden Sea (southern North Sea)

In the tidal inlet between the East Frisian islands of Langeoog and Spiekeroog, southern North Sea, a time-series station was set up in autumn 2002 as part of the research programme BioGeoChemistry of Tidal Flats run by the University of Oldenburg. The purpose of the station is to provide continuous data on physical, biological and chemical parameters. In addition to instruments recording basic hydrographic and meteorological parameters, the time-series station is equipped with acoustic Doppler profilers for measuring surface waves and current profiles. Compact optical spectrometers are being used for spectral measurements of seawater transmission and for daylight reflectance. Additional sensors were installed for measuring oxygen, nutrients and methane in the seawater. The data shall help to quantify the flux of dissolved and suspended matter between the backbarrier tidal flat and the open sea and to characterise the material transformation in the tidal flat area by biogeochemical processes over the tidal cycle. Due to its novel design, operation of the station is also possible during winter and under extreme weather conditions (gales, storm surges, and sea ice) when data sampling with conventional platforms such as research vessels, buoys, or smaller poles could not be performed in the past. In this way, time series of data are obtained, which include events that are most relevant to the evolution of this coastal area. The performance of the station and its equipment are presented with data covering 6 years of operation. Time series of air and water temperature as well as seawater salinity demonstrate the multiyear dynamics of these parameters in the East Frisian Wadden Sea. Hydrographic data collected under specific meteorological conditions such as gales and storm surges exemplify the all-weather capabilities of the station and its value for studying hydrographic processes in the Wadden Sea.