Performed Reflectivity Measurements Research Articles

Characterization of the temperature behavior of optimized SiC gratings emissivity

By exploiting experimentally measured optical properties of Silicon Carbide (SiC) at different temperatures, we recently showed based on a numerical analysis, that when SiC grating is heated, the position of its emissivity peak shifts towards higher wavelength values and its amplitude decreases. This proved the necessity to adapt the parameters of the grating to the temperature of measurements. In this previous article, we performed only numerical simulations for ideal devices. In order to check the validity of these results, we need some verifications from both the experimental and numerical points of view. In the herein study, we milled gratings on the same type of SiC for which the optical properties measurements were conducted. Then, we performed reflectivity measurements as a function of wavelength and temperature, in order to experimentally show the peak shift and to validate our optimized gratings. Hereby, this work provides guidelines for the design of optimized coherent thermal sources for different temperatures based on a combined numerical and experimental analysis.

Metallization of Shock-Compressed Liquid Ammonia.

Ammonia is predicted to be one of the major components in the depths of the ice giant planets Uranus and Neptune. Their dynamics, evolution, and interior structure are insufficiently understood and models rely imperatively on data for equation of state and transport properties. Despite its great significance, the experimentally accessed region of the ammonia phase diagram today is still very limited in pressure and temperature. Here we push the probed regime to unprecedented conditions, up to ∼350 GPa and ∼40 000 K. Along the Hugoniot, the temperature measured as a function of pressure shows a subtle change in slope at ∼7000 K and ∼90 GPa, in agreement with abinitio simulations we have performed. This feature coincides with the gradual transition from a molecular liquid to a plasma state. Additionally, we performed reflectivity measurements, providing the first experimental evidence of electronic conduction in high-pressure ammonia. Shock reflectance continuously rises with pressure above 50GPa and reaches saturation values above 120GPa. Corresponding electrical conductivity values are up to 1 order of magnitude higher than in water in the 100GPa regime, with possible significant contributions of the predicted ammonia-rich layers to the generation of magnetic dynamos in ice giant interiors.

Investigation and plasma cleaning of first mirrors coated with relevant ITER contaminants: beryllium and tungsten

In order to extend the investigation of the plasma cleaning of ITER first mirrors, a set of molybdenum mirrors was coated in a laboratory with ITER-relevant contaminants, namely beryllium and tungsten. Different coating techniques as well as several contaminant compositions were used to ensure a large variety of films to clean, completing a previous study conducted on mirrors exposed in the JET ITER-like wall (tokamak deposits) []. Due to the toxicity of beryllium, the samples were treated in a vacuum chamber specially built for this purpose. The cleaning was performed using capacitively coupled RF plasma and evaluated by performing reflectivity measurements, scanning electron microscopy, x-ray photoelectron spectroscopy and ion beam analysis. The removal of all types of contaminants was achieved by using different plasma compositions (argon, helium and mixtures of the two) with various ion energies (from 200–600 eV) and in some cases the mirror’s reflectivity was restored towards initial values. Pure helium discharges were capable of removing mixed beryllium/tungsten layers and oxidized molybdenum. In addition, no significant increase in the diffuse reflectivity of the mirrors was observed for the helium cleaning, though this was the case for some samples cleaned with argon. Helium is therefore appropriate for cleaning all mirrors in ITER leading to a possible cleaning regime where the entire vessel is filled with He and all mirrors are cleaned simultaneously without damaging their surfaces.

Angle Dependence of Diffuse Reflectance for a Microencapsulated Thermochromic Coating

ABSTRACTTraditional solar power applications largely avoid using the infrared spectrum. Nevertheless, this region makes up about 45% of the solar power spectrum and therefore represents an untapped resource. Temperature control of buildings represents a significant cost for both businesses and private consumers. We are interested in developing thermochromic materials for building coatings to help moderate solar infrared absorption and thereby offset temperature control costs for buildings. Our initial effort in this study has been to characterize materials which might represent starting points for our research. We previously designed and 3D-printed an optical test platform to perform reflectance measurements with an ultraviolet-visible-near infrared spectrometer over a spectral range from 200-1000nm. The test platform temperature can be adjusted in real time using Peltier modules. In this study, a sample of microencapsulated 7-anilino-3-diethylamino-6-methyl fluoran was studied by diffuse reflectance spectroscopy from 15-40 degrees Celsius. Scanning electron microscopy was used to characterize the dye particles. Temperature and spectral data were monitored while the sample temperature was adjusted. The visible diffuse reflectance from the sample increased from around 15% below the transition to more than 40% above the transition. A modification of this fluoran which extends the switching behavior into the infrared may be viable for passive thermo-optical switching in building coatings.

Plasma cleaning of beryllium coated mirrors

Cleaning systems of metallic first mirrors are needed in more than 20 optical diagnostic systems from ITER to avoid reflectivity losses. Currently, plasma sputtering is considered as one of the most promising techniques to remove deposits coming from the main wall (mainly beryllium and tungsten). This work presents the results of plasma cleaning of rhodium and molybdenum mirrors exposed in JET-ILW and contaminated with typical tokamak elements (including beryllium and tungsten). Using radio frequency (13.56 MHz) argon or helium plasma, the removal of mixed layers was demonstrated and mirror reflectivity improved towards initial values. The cleaning was evaluated by performing reflectivity measurements, scanning electron microscopy, x-ray photoelectron spectroscopy and ion beam analysis.

Photoexcited states of the harmonic honeycomb iridateγ−Li2IrO3

We report equilibrium and nonequilibrium optical measurements on the recently synthesized "harmonic" honeycomb iridate \gamma-Li$_2$IrO$_3$ (LIO), as well as the layered honeycomb iridate Na$_2$IrO$_3$ (NIO). Using Fourier transform infrared microscopy we performed reflectance measurements on LIO, from which we obtained the optical conductivity below 2 eV. In addition we measured the photoinduced changed in reflectance, \Delta R, as a function of time, t, temperature, T, and probe field polarization in both LIO and NIO. In LIO, \Delta R(t,T) is anisotropic and comprised of three T dependent components. Two of these components are related to the onset of magnetic order and the third is related to a photoinduced population of metastable electronic excited states. In NIO, \Delta R(t,T) has a single T dependent component that is strikingly similar to the electronic excitation component of \Delta R in LIO. Through analysis and comparison of \Delta R(t,T) for two compounds, we extract information on the onset of magnetic correlations at and above the transition temperature in LIO, the bare spin-flip scattering rate in equilibrium, the lifetime of low-lying quasiparticle excitations, and the polarization dependence of optical transitions that are sensitive to magnetic order.

Establishment and application of the 0/45 reflectance factor scale over the shortwave infrared.

This paper describes the establishment and application of the 0/45 reflectance factor scale in the shortwave infrared (SWIR) from 1100 to 2500 nm. Design, characterization, and the demonstration of a four-stage, extended indium-gallium-arsenide radiometer to perform reflectance measurements in the SWIR have been previously discussed. Here, we focus on the incorporation of the radiometer into the national reference reflectometer, its validation through comparison measurements, and the uncertainty budget. Next, this capability is applied to the measurement of three different diffuser materials. The 0/45 spectral reflectance factors for these materials are reported and compared to their respective 6/di spectral reflectance factors.

Plasma cleaning of ITER First Mirrors in magnetic field

To avoid reflectivity losses in ITER’s optical diagnostic systems, plasma sputtering of metallic First Mirrors is foreseen in order to remove deposits coming from the main wall (mainly beryllium and tungsten). Therefore plasma cleaning has to work on large mirrors (up to a size of 200×300mm) and under the influence of strong magnetic fields (several Tesla). This work presents the results of plasma cleaning of aluminium and aluminium oxide (used as beryllium proxy) deposited on molybdenum mirrors. Using radio frequency (13.56MHz) argon plasma, the removal of a 260nm mixed aluminium/aluminium oxide film deposited by magnetron sputtering on a mirror (98mm diameter) was demonstrated. 50nm of pure aluminium oxide were removed from test mirrors (25mm diameter) in a magnetic field of 0.35T for various angles between the field lines and the mirrors surfaces. The cleaning efficiency was evaluated by performing reflectivity measurements, Scanning Electron Microscopy and X-ray Photoelectron Spectroscopy.

Detector development for a high-flux neutron reflectometer

Neutron reflectometry is a powerful tool for investigating the surface and interfacial structures of various materials on the nanometer to submicrometer spatial range. We have been developing a horizontal-type neutron reflectometer, named SOFIA, at BL16 in J-PARC/MLF for investigating such interfacial structures, including those of free liquid surfaces. Utilizing the high-flux neutron beam at J-PARC, we have, until now, efficiently performed reflectivity measurements with SOFIA. However, the maximum count rate of the two-dimensional (2-D) detector currently in use will be insufficient for the full-power operation of J-PARC (1 MW) in the near future. In order to increase the count rate, we developed a new detector comprising 21 one-dimensional (1-D) detectors. 1-D detectors were used because neutron counts for a two-dimensional (2-D) detector can be reduced by dividing it into an array of 1-D detectors. In this study, we evaluated the performance of the newly developed detector and successfully carried out neutron reflectivity measurements using it.

Polarization properties of Mo/Si multilayers in the EUV range

We investigate polarization properties of two novel reflective Mo/Si multilayers (ML) in the EUV range using polarized synchrotron radiation at the BESSY-II storage ring facility. One of the Mo/Si ML is used as a retarder, the other one as an analyzer within the experimental setup of the BESSY soft-x-ray polarimeter. The analyzer multilayer is characterized by performing reflectivity measurements with s- and p-polarized light as a function of the incidence angle for different wavelengths. The characterization of the retarder multilayer consists of reflectivity measurements with s- and p-polarized light as a function of the wavelength for three different angles near normal incidence. In addition the phase retardance on reflection was determined for one angle of incidence as function of wavelength. Uncertainties of the phase retardance are estimated via the block bootstrap method. As an additional by-product of the ML characterization the Stokes parameters of the beamline could be determined. With the 8-axis BESSY polarimeter we have measured the complex reflection coefficients for the first time and established this ellipsometry technique as an additional probe to characterize multilayer optical elements.

REFocus: A new concept for a very high flux neutron reflectometer

One of the main challenges in neutron scattering is to increase the luminosity of the spectrometers. Here, a new concept of neutron reflectometer is presented. The aim is to maximize the use of the neutrons available in the guide by performing reflectivity measurements in parallel for all wavelengths. The expected flux gains are of the order of 20–50. The proposed design combines advanced neutron optical elements such as elliptical mirrors and graded multilayer monochromators. It does not require new technological developments and can be implemented right now on existing spectrometers. The REFocus set-up would enable to perform classical specular reflectivity measurements at least 10 times faster than on existing spectrometers.

Optical Sensor for Sulfur Dioxide Determination in Wines

A method for the determination of free and total sulfur dioxide in wines, based on the use of an optical sensor that employs a dichlorobis(diphenylphosphino)methane dipalladium I complex [Pd(2)(dppm)(2)Cl(2)] immobilized in a PVC membrane plasticized with o-nitrophenyloctylether (o-NPOE) is described. A sensing membrane [4.2% Pd(2)(dppm)(2)Cl(2), 20.8% PVC, and 75% o-NPOE] was adapted to the tip of a bifurcated optical fiber bundle to perform reflectance measurements at 550 nm. The detection system consisted of two cells (40 mL), which hold the sample solution (plus reagents) and the optical sensor, respectively. For the determination of free SO(2), a wine sample was mixed with H(2)SO(4) solution in the sample cell, into which N(2) was bubbled, providing mixing of the solutions and conducting the SO(2) formed toward the detection cell. For determination of total SO(2), a KOH solution was mixed with the wine in the sample cell. Afterward, an H(2)SO(4) solution was added to the cell, and then N(2) was bubbled to conclude the measurement. Linear responses up to 50 and 150 mg L(-1) were obtained for free and total SO(2), with detection limits of 0.37 and 0.70 mg L(-1), respectively. The repeatability of the method was evaluated by carrying out 10 measurements using a single wine sample, providing relative standard deviation values of 2.2 and 2.5% for free and total SO(2), respectively. The sensing membrane prepared from 10 muL of the cocktail solution lasted for 80 measurements, whereas those prepared from 200 muL can be used for 250 measurements. The method was applied to free and total SO(2) determination in wines, and the results did not show significant difference from those obtained with the Ripper reference method at a confidence level of 95%.

Introducing a mini-catamaran to perform reflectance measurements above and below the water surface

An innovative platform is tested to perform reflectance measurements at sea. This platform is a mini-catamaran with two hulls 1m long and set 0.7m apart, fitted with optical sensors. It can be used far away from an oceanographic ship to avoid its hull influencing the measurement. Reflectance measurements were performed with a TriOS radiance sensor placed +2cm or -2cm from the water surface and a TriOS irradiance sensor. Tests were carried out in calm seas and with cloud cover. The processing to derive marine radiances from raw measurements is detailed. When the radiance sensor is above the interface, it limits the sky reflections on the targeted surface and the radiance is identical to that deduced from measurements below the surface. When the sensor is placed at +3cm abovewater or higher, glint affects the measurements. The mini-catamaran shows a good ability to measure marine reflectance with an adapted measurement protocol. Except for very turbid waters, it seems preferable to perform upwelling radiance measurements below the surface.

The X-Ray Facility of the Physics Department of the Ferrara University

We will report on the equipment and performance of the X-ray facility of the University of Ferrara. Initially developed to test the PDS (Phoswich Detection System) instrument aboard the BeppoSAX satellite and to perform reflectivity measurements of mosaic crystal samples of HOPG (Highly Oriented Pyrolytic Graphite), with time the facility has been improved and its applications extended. Now these applications include test and calibration of hard X-ray (> 10 keV) detectors, reflectivity measurements of hard X-ray mirrors, reflectivity tests of crystals and X-ray transparency measurements. The facility is being further improved in order to determine the optical axis mosaic crystals in Laue configuration within a project devoted to develop a hard X-ray (> 60 keV) focusing optics (Pisa, A. et al.: in press, Feasibility study of a Laue lens for hard X-rays for space astronomy, SPIE Proc., 5536).

Optical properties of molecular beam epitaxy-grown ZnSexTe1−x II–VI semiconductor alloys

A series of ZnSexTe1−x alloys with varying compositions that cover the entire range between the two binaries ZnSe and ZnTe were grown to determine the index of refraction, n, as a function of both wavelength and the alloy concentration. The ZnSexTe1−x alloys were all grown directly on GaAs (100) substrates using molecular beam epitaxy. X-ray diffraction experiments were performed to determine the quality and the compositions of each of the ZnSexTe1−x specimens. The n was then measured with an accuracy of at least 0.1% at four discrete wavelengths using a prism coupler method. Since these data points are inadequate to ascertain, an accurate dispersion of the index of refraction, we next performed reflectivity measurements on each of the samples to complement the prism coupler data. The reflectivity and the prism coupler data allow us to arrive at the dispersion relations of the indices of refraction of ZnSexTe1−x ternary alloys very accurately. We also find that, unlike most semiconductors, the values of n of ZnSexTe1−x alloys do not follow an inverse relationship with the energy gap.

Optical investigation of the metal-insulator transition in NdBa 2Cu 3O x A comparison with YBa 2Cu 3O x

We have performed reflectance measurements on the (001) surfaces of twinned single crystals of NdBa 2Cu 3O x . The oxygen concentration x was varied between 6 ≤ x ≤ 7. The results were compared to former investigations on YBa 2Cu 3O x . The different dependence of the electronic transport properties on the oxygen content of both compounds can be explained by the different distributions of oxygen amongst the CuO chains.

Resonant mode in the modified Huesler alloy U 0.85Th 0.15NiSn

We performed reflectance measurements from 10–2500 cm −1 and from room temperature to 10 K for U 1− x Th x NiSn. A semiconducting gap was observed at about 500 cm −1 for all the temperatures. There was a marked reduction in oscillator strength of the gap at 10 K indicating a partial destruction of the gap. Four phonon lines were observed at 137, 156, 172 and 185 cm −1. A temperature and frequency dependent mode was also seen at lower frequencies. In the semiconducting state the mode was attributed to impurity levels within the gap whereas in the metallic state the mode was due to resonance between the conduction electrons and the U f-level.

Optical investigation of the metal-insulator transition in Y 1−xPr xBa 2Cu 3O 7−δ

We have performed reflectance measurements on (001) surfaces of several Y 1−xPr xBa 2Cu 3O 7−δ single crystals in an energy range from 50 meV up to 6 eV. The Pr content x was varied between x=0 and x=1. Using a Kramers-Kronig transformation and fitting a Drude-Lorentz model to the reflectance spectra, we determined the dynamic conductivity. On the basis of optical sum rules we discuss the controverse question if the supression of the metallic and superconducting behaviour with increasing Pr content is the result of a localization of the free carriers or the compensation of the oxygen doping.

C-axis reflectance and the superconducting order parameter of YBa 2Cu 3O 7−δ

We have performed reflectivity measurements with E ̄ ∥ c on superconducting YBa 2Cu 3O 7−δ single crystals in the energy range from 5 meV to 600 meV. The temperature was varied between 10 K and 300 K. At room temperature the energy range was extended to 6 eV to improve the basis for a Kramers-Kronig analysis. At low temperature each sample shows a reflectivity edge at an energy of about kT c . With decreasing temperature we observe a rapid decrease of the electronic scattering rate below T c . Using a simple two-fluid-model the analysis of the data shows evidence for a non BCS-like superconducting order parameter.

Development status of Bragg hard—X-ray concentrators for space astronomy

In this paper we report the development status of a research programme devoted to study the possibility of utilizing the Bragg diffraction technique to concentrate hard X-rays. We present the results of our theoretical studies. We discuss the expected performances of a hard—X-ray (>10 keV) concentrator which will be made of nested paraboloidal mirrors of graphite (002) mosaic crystals in a reflection configuration. We also report the differences in performance between a perfect mirror geometry and an imperfect geometry. We give a short description of the X-ray test facility which has been set up to perform reflectivity measurements of flat samples of mosaic crystals. We also discuss perspectives of this programme in the context of the space astrophysics.