ZnSe Window Research Articles

Active correction of window Faraday effects for ITER laser diagnostics

Measurement of the change in polarization of a laser beam traversing a magnetized plasma is a standard diagnostic technique for extracting key plasma parameters, including density and current profile. Depending on the polarization orientation of the incident laser beam relative to theplasma magnetic field, the polarization change is denoted as either Faraday rotation or Cotton-Mouton effect. On ITER three laser diagnostics will make use of this effect to make their measurements. Unfortunately, this effect is also evident when the laser beam passes through the vacuum window. The large magnetic field and finite verdet constant of the window material mean that on ITER this effect — in particular faraday rotation — is non-negligible, and needs to be disentangled from the desired measurement parameter. The Toroidal Interferometer-Polarimeter (TIP) and Density Interferometer-Polarimeter (DIP), in particular, are affected. Both diagnostics use lasers in the 5–10 μm range, and will use zinc-selenide (ZnSe) as the vacuum window material. In order to compensate for the unwanted window distortion a sensor is being developed to monitor the magnetic field perpendicular to the window and activelycorrectfor the faraday rotation in real time. The sensor consists of an inductive coil closely fitted just in front of the window disc. It comprises several turns of fine wire in center-tap configuration. Both the raw voltage signal, as well as the integrated signal, will be monitored to estimate the magnetic field through the window disk. The system is designed to measure fields up to B <1 T with an accuracy of 0.01 T, at frequencies of D.C. to 1 kHz. The backend electronics will leverage off similar technology developed for other ITER magnetics systems. Using the real-time magnetic field information, in conjunction with published and/or measured data on the verdet constant of the ZnSe window material, in-house developed software will estimate the faraday rotation induced by passing through the window.An initial prototype of the sensor has been fabricated and results from preliminary characterization trials of the system are presented. Detailed testing is planned for the future using the DIP system prototype currently under development.

Numerical simulation on the impurity photovoltaic (IPV) effect in c-Si wafer-based dual-heterojunction solar cell

The impurity photovoltaic effect (IPV) with thallium (TI) impurity has theoretically been investigated in crystalline silicon (c-Si) wafer reigned dual-heterojunction (DH) solar cell that ensures an extended absorption of longer wavelength light with zinc selenide (ZnSe) window and aluminium antimonide (AlSb) back surface layers. The results imply that the incorporation of impurity enhances the photocurrent while the dual-heterojunction ensures the higher V OC of the proposed solar cell structure. The pristine Si (150 µm wafer) solar cell exhibits a power conversion efficiency (PCE) of 35.04% with J SC = 38.85 mA/cm 2 and V OC = 1.05 V, respectively. On the contrary, the introduction of Tl impurity within the bandgap of absorber enhances the PCE to 44.47%, with a J SC = 48.95 mA/cm 2 , V OC = 1.063 V and FF= 85.46%, respectively. This augmentations of the V OC and J SC and hence PCE is originated from the DH structure and longer wavelength light absorption due to impurity-assisted two-step photon upconversion phenomena in the solar cell. • IPV effect in an n + -p-p + Si DH solar cell with Tl impurity has been simulated. • ZnSe and AlSb have been used as window and BSF layers, respectively. • The optimized metal contacts Ti (cathode) and Ni (anode) has been established. • A maximum J SC of 48.95 mA/cm 2 and PCE= 44.47% with V OC = 1.063 V has been achieved. • n + - ZnSe /p- Si /p + - AlSb DH solar cell with Tl impurity shows potential in future.

Design of a highly efficient FeS2-based dual-heterojunction thin film solar cell

ABSTRACT This article demonstrates a highly efficient FeS2-based n-ZnSe/p-FeS2/p+-AlxGa1-xSb dual-heterojunction thin film solar cell using SCAPS-1D simulator. The study has been carried out taking the physical parameters from the literature. The influence of thickness, doping, and defect concentration of ZnSe, FeS2, and AlxGa1-xSb layers on the photovoltaic performance of the solar cell has been investigated in details. The power conversion efficiency (PCE) of the n-ZnSe/p-FeS2 single-heterojunction solar cell is ~23.22% with JSC = 47.52 mA/cm2, VOC = 0.59 V, and FF = 82.62%, respectively. The PCE of the solar cell further increases to ~36.75% with JSC = 48.13 mA/cm2, VOC = 0.94 V, and FF = 80.75%, respectively with the insertion of AlxGa1-xSb back surface field (BSF) layer. This increase in PCE is mainly due to the enhancement of VOC which is resulted from the suitable band alignment of the dual-heterojunction devices. These results indicate that FeS2-based dual-heterojunction thin film solar cell with ZnSe and AlxGa1-xSb window and BSF layers, respectively, is a potential candidate to fabricate high efficiency thin film solar cell for harvesting solar energy in the future.

An In-Situ Transmission Fourier Transform Infrared Study on the Interaction Mechanism of Plasma with Nano-Catalyst for CO₂ Methanation.

The effects of discharge conditions and catalysts on CO₂ methanation under the plasma were investigated via In-Situ transmission FTIR and OES analysis. The bare Al₂O₃, Ni/Al₂O₃ and Ru/Al₂O₃ catalysts were coated on the ZnSe window using the modified sol-gel method for In-Situ transmission FTIR analysis. It was confirmed from the OES analysis that the intensity of excited hydrogen increased in all catalysts as the discharge frequency and voltage increased, and the increment of H+ peak intensity was the largest in the Ru/Al₂O₃ catalyst. In addition, it was found from the In-Situ transmission FTIR analysis that the O-H band was all disappeared as the frequency and voltage increased. In conclusion, the increased H+ with the decomposition of O-H led to the increase in the CH₄ conversion, resulting in the highest CH₄ conversion in the Ru/Al₂O₃ catalyst.

Design and application of a high-pressure combustion chamber for studying propellant flames with laser diagnostics.

This manuscript presents the design and initial application of a high-pressure combustion chamber (HPCC). The HPCC exhibits several unique design attributes to enable high-fidelity studies of propellant-combustion physics at high pressures. The HPCC employs a flangeless and weldless design to provide a compact, easy to access, and relatively light weight (for its size and pressure capability) test chamber. It has a cylindrical test volume of 13.1 L and is capable of operating at pressures from approximately 0.4 mbar to 200 bar. The vessel is equipped with a ZnSe window to enable the laser ignition of propellants and energetic materials and 4 sapphire windows (2″ diameter and 4″ × 2″ slots) to enable the use of multiple optical diagnostics spanning the ultraviolet to mid-infrared. The sapphire windows are mounted in plugs with adjustable length to bring the windows inside of the test volume and facilitate line-of-sight optical measurements. The vessel can be accessed from the top and bottom via removable 5″ diameter plugs, and the bottom plug can be modified to enable studies of gaseous jets and flames. Some of the HPCC's testing capabilities are demonstrated via high-speed IR imaging and laser-absorption-spectroscopy measurements of temperature and CO in laser-ignited HMX (i.e., 1,3,5,7-tetranitro-1,3,5,7-tetrazoctane) flames at pressures from 2 to 25 bar.

Infrared spectroscopy for a quantitative determination of CH3-nClnCOCl in TiCl4

Infrared spectroscopy permits a determination of the concentration of CHCl2COCl, CH2ClCOCl and CCl3COCl as the organic impurities in TiCl4. In this study, an infrared spectrometer with ZnSe window and the cell of PTFE was assembled, and used to determine the concentration of three organic impurities. The detection limits of CCl3COCl, CHCl2COCl, CH2ClCOCl were determined as 3.16×10-3 μg/g 1.92×10-3 μg/g and 1.55×10-2 μg/g respectively. The new method is applied to quality control of refined TiCl4 from titanium sponge.

Monitoring wine aging with Fourier transform infrared spectroscopy (FT-IR)

Oak wood has commonly been used in wine aging but recently other wood types such as Acacia and Chestnut, have attracted the interest of the researchers due to their possible positive contribution to wine quality. However, only the use of oak and chestnut woods is approved by the International Enological Codex of the International Organisation of Vine and Wine. In this study Fourier Transform (FT)-mid-infrared spectroscopy combined with Discriminant Analysis was used to differentiate wines aged in barrels made from French oak, American oak, Acacia and Chestnut and in tanks with oak chips, over a period of 12 months. Two red (Mandilaria, Kotsifali) and two white (Vilana, Dafni) native Greek grape varieties where used to produce four wines. The Fourier Transform Infrared (FT-IR) spectra of the samples were recorded on a Zinc Selenide (ZnSe) window after incubation at 40 °C for 30 min. A complete differentiation of the samples according to both the type of wood used and the contact time was achieved based on their FT-IR spectra.

An Investigation into III–V Compounds to Reach 20% Efficiency with Minimum Cell Thickness in Ultrathin-Film Solar Cells

III–V single-junction solar cells have already achieved very high efficiency levels. However, their use in terrestrial applications is limited by the high fabrication cost. High-efficiency, ultrathin-film solar cells can effectively solve this problem, as their material requirement is minimum. This work presents a comparison among several III–V compounds that have high optical absorption capability as well as optimum bandgap (around 1.4 eV) for use as solar cell absorbers. The aim is to observe and compare the ability of these materials to reach a target efficiency level of 20% with minimum possible cell thickness. The solar cell considered has an n-type ZnSe window layer, an n-type Al0.1Ga0.9As emitter layer, and a p-type Ga0.5In0.5P back surface field (BSF) layer. Ge is used as the substrate. In the initial design, a p-type InP base was sandwiched between the emitter and the BSF layer, and the design parameters for the device were optimized by analyzing the simulation outcomes with ADEPT/F, a one-dimensional (1D) simulation tool. Then, the minimum cell thickness that achieves 20% efficiency was determined by observing the efficiency variation with cell thickness. Afterwards, the base material was changed to a few other selected III–V compounds, and for each case, the minimum cell thickness was determined in a similar manner. Finally, these cell thickness values were compared and analyzed to identify more effective base layer materials for III–V single-junction solar cells.

Formation and stability of bulk carbonic acid (H2CO3) by protonation of tropospheric calcite.

Organic acids play an important role in the acidification of our atmosphere. These weak acids can contribute up to 60 % of the free airborne acidity. By far the most abundant organic acids are the C1 and C2 monocarboxylic acids, formic acid (HCOOH) and acetic acid (CH3COOH), which show mixing ratios in the gas phase ranging up to 20 ppb over land1,2 and down to 0.2 ppb in the remote oceanic boundary layer or troposphere.3,4 These acids are partitioned between the gas phase and the particulate phase, where roughly one half to two thirds can be found in particulate matter (PM2.5).2 The most important removal mechanism is dry deposition, which accounts for more than 90 % of the total organic acid deposition budget. The remaining fraction is removed by rain as particulate-phase acids, whereas removal by chemical reactions is negligible.1,5 In addition to the two most important organic acids, C3–C10 aliphatic monocarboxylic acids1 and C2–C11 aliphatic dicarboxylic acids1,2,6–11 as well as aromatic carboxylic acids1 have also been observed in air. The water-soluble fraction of organic carbon can on average consist of 35 % mono- and dicarboxylic acids.12 While the C2-dicarboxylic acid, oxalic acid (COOH)2, is commonly observed in all field studies, the C1-dicarboxylic acid, carbonic acid (H2CO3), has barely received any attention, mainly because it is thought that it immediately decomposes to water and carbon dioxide. However, it has previously been shown that gaseous, water-free carbonic acid is surprisingly stable,13 that amorphous and crystalline solids of pure carbonic acid can be produced and stored without decomposition at temperatures up to 230 K even in the presence of water14 and that this solid can be sublimed at, for example, 220 K and recondensed in vacuo at surfaces of lower temperature.15

Quantitative SNIFTIRS studies of (bi)sulfate adsorption at the Pt(111) electrode surface

Subtractively normalized interfacial Fourier transform infrared reflection spectroscopy (SNIFTIRS) was applied to study (bi)sulfate adsorption on a Pt(111) surface in solutions of variable pH while maintaining a constant total bisulfate/sulfate ((bi)sulfate) concentration without the addition of an inert supporting electrolyte. The spectra were recorded for both the p- and s-polarizations of the IR radiation in order to differentiate between the IR bands of the (bi)sulfate species adsorbed on the electrode surface from those species located in the thin layer of electrolyte. The spectra recorded with p-polarized light consist of the IR bands from both the species adsorbed at the electrode surface and those present in the thin layer of electrolyte between the electrode surface and ZnSe window whereas the s-polarized spectra contain only the IR bands from the species located in the thin layer of electrolyte. A new procedure was developed to calculate the angle of incidence and thickness of the electrolyte between the Pt(111) electrode surface and the ZnSe IR transparent window. By combining these values with the knowledge of the optical constants for Pt, H(2)O and ZnSe, the mean square electric field strength (MSEFS) at the Pt(111) electrode surface and for thin layer of solution were accurately calculated. The spectra recorded using s-polarization were multiplied by the ratio of the average MSEFS for p- and s-polarizations and subtracted from the spectra recorded using p-polarization in order to remove the IR bands that arise from the species present within the thin layer cavity. In this manner, the resulting IR spectra contain only the IR bands for the anions adsorbed on the Pt(111) electrode surface. The spectra of adsorbed anions show little change with respect to the pH ranging from 1 to 5.6. This behavior indicates that the same species is predominantly adsorbed on the metal surface for this broad range of pH values and the results suggest that sulfate is the most likely candidate for this adsorbate.

Radiance calibration of CRISTA-NF

The CRISTA-NF instrument is the airborne version of the CRISTA satellite infrared limb sounder. It has been successfully flown on the Geophysica research airplane during a test campaign in July 2005, during the SCOUT-O3 Tropical Aircraft Campaign in November/December 2005 and during the AMMA campaign in August 2006. Radiance calibrations of the airborne instrument are more complex compared to the satellite instrument because the vacuum shell of CRISTA-NF is confined by a ZnSe (zinc–selenide) window and the detectors can thermally drift during measurement flights. By comprehensive radiance calibrations with a blackbody source the window’s emissivity and transmissivity are determined and the dependence of the instrument sensitivity on the detector temperature is characterized. Taking these effects into account, the remaining radiance error of the calibration is smaller than 3%.

Wall-Propelled, In-Tube Propulsion with Repetitive-Pulse Laser Ablation

Proof-of-principle experiments of in-tube propulsion in which the propellant was supplied from the launch tube wall were conducted. The launch tube had a 25 mm × 25 mm square inner cross-section. A pair of opposing launch tube walls were made of polyacetal (POM), which was ablated using repetitive Transeversely-Excited Atmospheric (TEA) CO2 laser pulses. The laser beam was sent through a ZnSe window at the tube bottom to the symmetric parabolic surfaces of the projectile, and focused onto the ablator surfaces. The momentum coupling coefficient was measured from a vertical launch trajectory. When the breech of the launch tube was plugged, a momentum coupling coefficient of 4 mN-s/J at least was obtained. Even when the breech was connected to a vacuum chamber at a pressure lower than 20 Pa, the projectile could be vertically launched with a constant momentum coupling coefficient of 0.14 mN-s/J, the value of which was the same order as that obtained by directly irradiating a laser pulse onto a POM ablator.

Uncooled matrix IR detector based on optoacoustic cells and optoelectronic reading system

The matrix structure 200 × 200 of optoacoustic cells (OAC) for uncooled IR imager with optoelectronic reading system is fabricated and investigated at the first time. Cells 100 μm in diameter shaped on ZnSe window and filled by xenon. Photosensitive layer consisted of SiO2 film with adsorption range 8–14 μm. Flexible membrane 0.1 μm of thick consisted of SiO2 and Al films. Radiation temperature sensitivity and noise equivalent power with optics f/1 were 0.15 K/Hz1/2 and 10 nW/Hz1/2, respectively, and the thermal response time was below 30 ms.

In situ monitoring of the solution‐mediated polymorphic transformation of glycine: characterization of the polymorphs and observation of the transformation rate using Raman spectroscopy and microscopy

AbstractThe aim of this work was to investigate the mechanism and progression of the solution‐mediated polymorphic transformation and crystallization of glycine. The identification of the α‐ and γ‐forms of glycine crystals was performed using powder X‐ray diffraction (PXRD), Raman microscopy and in situ probe Raman spectroscopy. The influence of the addition of NaCl and of the process parameters such as saturation temperature, seed size and stirring speed on the transformation behavior from the metastable α‐ form to the stable γ‐ form was examined. In situ probe Raman spectroscopy was used to monitor the solid‐phase properties—polymorphic composition. Fourier transform infrared spectroscopy (FTIR) with a ZnSe window was used to track the liquid‐phase concentration at different times. Besides, the polymorphic transformation of glycine in the solvent was also examined in situ using a microscope with a heating/cooling stage. The integration of the different offline and in situ analytical measurement techniques greatly assisted in accurately and quantitatively perceiving the fundamental phenomena that govern the transformation process. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Off-Line Direct Deposition Gas Chromatography/Surface-Enhanced Raman Scattering and the Ramifications for On-Line Measurements

Surface-enhanced Raman spectra (SERS) of molecules separated by gas chromatography (GC) were measured off-line by condensing the analyte on a moving, liquid-nitrogen-cooled ZnSe window on which a 5 nm layer of silver had been formed by physical vapor deposition. After the components that eluted from the chromatograph had been deposited, the substrate was allowed to warm up to room temperature and transferred to the focus of a Raman microspectrometer where the spectrum of each component was measured. Band intensities in the spectrum of 3 ng of caffeine prepared in this way were approximately the same as in the spectrum of bulk caffeine. By making some logical assumptions, it was shown that identifiable GC/SERS spectra of 30 pg of many molecules could be measured over a 300 cm(-1) region in real-time and that if an optimized substrate were used the minimum identifiable quantity could be reduced to 1 pg or less.

Analysis of uncertainties in infrared camera measurements of a turbofan engine in an altitude test cell

The infrared (IR) signature of a jet aircraft engine in altitude operation is a key component for the design of effective IR countermeasures and low-emission engines. Predicting the signature with radiometric models is widely accomplished, but measurements in situ are crucial for model verification. The altitude test cell provides a venue for measuring the IR signature in a simulated altitude environment, but the facility is designed for testing engines, not IR imaging. As a result, the imaging in the test cell is laden with measurement uncertainty due to stray radiation from the facility structure, hot exhaust gases, and the measurement equipment itself. Post-processing using correction factors is necessary to extract the engine signal from the stray radiation. This research investigated the uncertainties in measuring the IR signature of a turbofan engine inside an altitude test cell. The engine is measured by an IR camera immersed in the hot exhaust gases 35 feet downstream from the on-engine axis view. A protective enclosure and zinc selenide (ZnSe) window shield the camera from the heat and vibrations of the plume. The requirements for the IR measurement system include the apparent intensity and radiance of the visible engine surfaces in three bands of operation, two Medium Wave IR (MWIR) bands and one Long Wave IR (LWIR), with a spatial resolution of 1 in. To explore the extent of the measurement uncertainties, a radiometric model of the altitude test cell is formulated to quantify the engine and stray flux. To increase the fidelity of the model, the ZnSe window, a source of stray radiation, is characterized through measurements and experimentation. The resulting data is employed in the radiometric model. Specific measurement conditions at which the stray radiation is 5% or less of the total radiation are then derived, thereby decreasing the necessity for post-processing correction factors. These conditions are derived for the 3–4-, 4.5–5-, 8–9- and 8–12-μm bands using a parametric analysis. Two LWIR bands are considered to provide insight into specific previous measurements made with a quantum-well IR photo-detector (QWIP, roughly 8–9 μm), as well as potential future measurements made using broader band imagers (e.g., HgCdTe at 8–12 μm). A sensitivity analysis in the style of a Monte Carlo simulation is also performed to gauge the uncertainty in the radiometric model calculations.

Fourier Transform Infrared-Probed O(3P) Microreactor: Demonstration with Ethylene Reactions in Argon Matrix

To demonstrate the development of an oxygen atom microreactor in the form of liquid-helium-cooled solid argon matrix deposited on an infrared (IR) window, the oxidation of ethylene by mobile O atoms has been investigated. O atom diffusion through the argon matrix is confirmed and used to examine ethylene-oxygen atom reactions. In a bench-scale matrix isolation system probed with a Fourier transform infrared (FT-IR) spectrometer, matrices of solid Ar at 8-10 K doped with NO2 and ethylene have been prepared on a ZnSe window within an evacuated cryostat. The matrices have been photolyzed using 350-450 nm photons, and the reaction products resulting from the reaction of O(3P), one of the photolysis products of NO2, with ethylene have been identified using FT-IR and a Gaussian 98W simulation program. These products include oxirane, acetaldehyde, ethyl nitrite radical, and ketene. The temperature effect in the range of 10-30 K on the products formed has also been investigated. The reaction mechanisms are discussed and the viability of the solid Ar matrix being a low temperature microreactor to examine reaction mechanisms of mobile oxygen atoms is elaborated.

High-power CO2 laser design “from resonator end mirror to cutting lens focal point”

An algorithm is derived that allows calculating all optical parameters relevant to the design of a high-power CO2 laser, taking into account the practical needs of a flying-optics type of laser cutting machine. The novelty of the approach taken is that the resonator and the beam delivery optics are treated simultaneously, which allows for greater flexibility in design. To begin with, the often-used optical configuration of a stable resonator combined with a beam expander for collimation is modeled and optimized. The remaining focal shift over the cutting table, mainly due to the fact that the part of the beam close to the resonator still has appreciable wavefront curvature variation, is calculated. The resulting function is programmed into the machine CNC, which continuously adjusts the lens position depending on the actual beam length, to compensate for this effect. Next, attention is paid to the well-known problem of changing beam parameters with thermal load of the output coupler. It is found necessary to model both mechanical deformation of the ZnSe window and lensing due to the temperature dependent index of refraction. The former is derived from a finite element model, for the latter, the formula of Miyamoto et al. [Proc. SPIE 1276, 112 (1990)] is used. Finally, as an example of novel resonator designs studied using this approach, the characteristics of an intracavity reflective telescope are determined for two different goals: first, to increase the fundamental mode spot size for the given resonator (and hence to improve beam quality without sacrificing power), and second to preserve beam quality when extra resonator layers are added to increase power. The beam is modeled using the concept of the “embedded Gaussian” and the “complex radius of curvature” due to Siegman [Lasers (University Science Books, CA, 1986)].

Landsat-5 Thematic Mapper outgassing effects

A periodic 3% to 5% variation in detector response affecting both image and internal calibrator (IC) data has been observed in bands 5 and 7 of the Landsat-5 Thematic Mapper. The source for this variation is thought to be an interference effect due to buildup of an ice-like contaminant film on a ZnSe window, covered with an antireflective coating (ARC), of the cooled Dewar containing these detectors. Periodic warming of the dewar is required in order to remove the contaminant and restore detector response to an uncontaminated level. These effects in the IC data have been characterized over four individual outgassing cycles using thin-film models to estimate transmittance of the window/ARC and ARC/contaminant film stack throughout the instrument lifetime. Based on the results obtained from this modeling, a lookup table procedure has been implemented that provides correction factors to improve the calibration accuracy of bands 5 and 7 by approximately 5%.

In situ laser annealing system for real-time surface kinetic analysis

For real-time analysis during thermal annealing, a continuous wave CO2 infrared laser was coupled to a surface analysis system equipped for x-ray photoelectron spectroscopy (XPS) and ion scattering spectroscopy (ISS). The laser beam was directed into the vacuum chamber through a ZnSe window to the back side of the sample. With 10 W laser output, the sample temperature reached 563 K. The chamber remained below 10−8 Torr during annealing and allowed XPS and ISS data to be gathered as a function of time at selected temperatures. As a test example, real time Cu2O reduction at 563 K was investigated.