Optical Emittance Research Articles

The Effect of Pigment Material on the Optical Absorbance, Emittance, and Wear Resistance of Black Anodized Coatings: A Case Study on 7075 Aluminum Alloy

The Effect of Pigment Material on the Optical Absorbance, Emittance, and Wear Resistance of Black Anodized Coatings: A Case Study on 7075 Aluminum Alloy

Analysis of the absorptance and emittance in particle curtains by means of a discrete MCRT method

Apparent optical properties, absorptance and emittance, in particle curtains are analyzed by means of a discrete Monte Carlo Ray-Tracing model. The effect of solid volume fraction, particle diameter and curtain thickness on these properties is investigated for two types of particles with different absorptivity and emissivity: sand and CARBO HSP. Absorptance and emittance achieved by curtains made of these particles are greater than the values of absorptivity and emissivity of material. The increase in curtain absorptance/emittance compared to the particle absorptivity/emissivity is higher as the particle property is poorer, such as in sand. Both absorptance and emittance are maximum for opaque curtains, which entails high thicknesses. Assuming opaque curtains, the absorptance and emittance increase as the solid volume fraction decreases. The results obtained with the Monte Carlo Ray-Tracing model are used to estimate particle curtain radiative losses including emission and reflection losses. If material properties absorptivity and emissivity are used instead of the obtained curtain properties absorptance and emittance, sand curtain losses are up to 35 pp and only 9 pp in the case of CARBO HSP. Absorptivity is more important than emissivity, that is, it is preferable having high absorptivity than low emissivity to achieve low radiative losses. Emission losses are less important than reflected losses being very similar in both types of curtains. Sand curtains lose 33% of the incoming power while CARBO curtains lose only 7%. Radiative losses are significantly higher than advection losses in sand curtains. However, in CARBO curtains, advection losses are higher.

Characteristics of Al & Ti oxide-thin films for thermal solar energy selective absorption applications

Controlled oxidation of sputtered layers of Ti and Al results oxide layers with nano-sized thickness comparable to thermal solar selective absorber layers. In this work, RF magnetron sputtering was used to obtain thin layers of Al and Ti on substrates of stainless steels (St. St). Deposited thin films were oxidized at 400 °C and 800 °C for 4 hours and 1 hour, respectively. The as-deposited Ti, and Al layers were air–oxidized and their optical absorbance and emittance were studied. Microstructure, surface topography, structure and new phases formed after oxidation were characterized by scanning electron microscope (SEM), atomic force microscope (AFM), and X-ray diffraction (XRD). Thin films optical properties were investigated by spectrophotometer & Fourier Transform Infrared (FTIR) Spectroscopy. The new microstructures exhibited a dual metallic and oxide nature. Deposited thin film of Ti had maximum absorbance and lowest emittance about 90% and 1.8% respectively; while after oxidation, the deposited layers changed their selective absorbance pattern. The absorbance values increased, and the emittance values decreased for all wave lengths in the infrared (IR) range. The effect of the oxidation process of both Ti thin film and Al thin film was compared. The Al thin film showed lower absorbance in as-deposited and oxidized states.

Optical and structural properties of nanostructured copper oxide thin films as solar selective coating prepared by spray pyrolysis method

AbstractCopper (II) oxide thin films were prepared by spray pyrolysis method on soda-lime glass substrates using copper acetate precursor solution. Influence of substrate temperature on structural and optical properties was investigated. Structural analysis of these layers were carried out by X-ray diffraction (XRD). Single phase nature and high crystallinity of CuO nanostructures were observed on XRD patterns. The general appearance of the films was uniform and black in color. FT-IR transmittance spectra confirmed the results from the XRD study. Selective solar absorber coatings of copper oxide (CuO) on stainless steel substrates was prepared by spray pyrolysis method. Effect of deposition temperature on optical properties of thin films was investigated. Optical parameters, absorbance (α) and emittance (α) were evaluated from reflectance data. It can be deduced that the porous structure, such as a light traps, can greatly enhance absorbance, while the composition, thickness and roughness of thin films can greatly influence the emissivity. Single phase nature and high crystallinity of CuO nanostructures were observed by XRD patterns. Solar absorbance of thin films were in the range of 85 % to 92 %.

Optical and infrared properties of glancing angle-deposited nanostructured tungsten films.

Nanotextured tungsten thin films were obtained on a stainless steel (SS) substrate using the glancing-angle-deposition (GLAD) method. It was found that the optical absorption and thermal emittance of the SS substrate can be controlled by varying the parameters used during deposition. Finite-difference time-domain (FDTD) simulations were used to predict the optical absorption and infrared (IR) reflectance spectra of the fabricated samples, and good agreement was found between simulated and measured data. FDTD simulations were also used to predict the effect of changes in the height and periodicity of the nanotextures. These simulations show that good control over the absorption can be achieved by altering the height and periodicity of the nanostructure. These nanostructures were shown to be temperature stable up to 500°C with the addition of a protective HfO2 layer. Applications for this structure are explored, including a promising application for solar thermal energy systems.

Platinum containing amorphous hydrogenated carbon (a-C:H/Pt) thin films as selective solar absorbers

We have investigated a double-cermet structured thin film in which an a-C:H thin film was used as an anti-reflective (AR) layer and two platinum-containing amorphous hydrogenated carbon (a-C:H/Pt) thin films were used as the double cermet layers. A reactive co-sputter deposition method was used to prepare both the anti-reflective and cermet layers. Effects of the target power and heat treatment were studied. The obtained films were characterized using X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy. The optical absorptance and emittance of the as deposited and annealed films were determined using UV–vis-NIR spectroscopy. We show that the optical absorptance of the resulting double-cermet structured thin film is as high as 96% and remains to be 91% after heat treatment at 400 °C, indicating the thermal stability of the film.

Reactively co-sputter deposited a-C:H/Cr thin films: Material characteristics and optical properties

Various chromium-containing amorphous hydrogenated carbon (a-C:H/Cr) coatings were deposited on oxygen-free copper and silicon substrates for use as solar selective absorber coatings. The deposition was performed using a magnetron co-sputter deposition method under various methane/Ar ratios, ranging from 0 to 8%. The obtained films were characterized using glazing incident X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, secondary ion mass spectrometer, and X-ray photoelectron spectroscopy. The optical absorptance and emittance at 100°C were determined using UV–vis-NIR spectroscopy and Fourier transform infrared spectrometry, respectively. Effects of the material characteristics on the optical properties are reported and discussed.

Optical properties of nanostructured tungsten in near infrared range

In nuclear fusion devices, infrared (IR) imaging diagnostics have been widely used for the temperature measurement of in-vessel surfaces. For the diagnostics, variations of the optical emittance and reflectance of wall materials will be an essential issue to measure the temperature correctly. In this study, variations in the optical properties in near IR range of tungsten exposed to helium plasmas were experimentally investigated in detail by observing the radiation spectrum from a heated sample. By the exposure to the helium plasma, nanostructures were grown from the surface, while the nanostructures were annealed out when the surface temperature was raised without helium ion irradiation. The optical emittance was measured from the radiation spectrum in the wavelength range 1400–4000 nm; it was revealed that the emittance significantly altered for a short time period in the formation and annealing processes of nanostructures. The influence of the variation in the optical properties on the IR diagnostics is discussed.

Near Infrared Radiation from Heated Nanostructured Tungsten

Helium plasma irradiation to metals leads to morphology changes in nanometer scales by the formation of helium bubbles. The nanostructure significantly alters the optical property of the metal. In this study, near infrared radiations from a heated nanostructured tungsten are measured with a spectrometer. Energy balance between the influx of plasma and radiation from the sample is discussed in terms of the optical emittance. It is shown that the optical emittance is increased considerably by the morphology change in the range from visible to near infrared, and the efficiency of radiation is increased by two to three times.

Role of surface plasmon polaritons in the optical response of a hole pair

The optical emittance of a hole pair perforated in an opaque metal film is studied from first-principles using the coupled-mode method. The geometrical simplicity of this system helps to understand the fundamental role played by surface plasmon polaritons (SPPs) in its optical response. A SPP interference model without fitting parameters is developed from the rigorous solution of Maxwell's equations. The calculations show that the interference pattern of the hole pair is determined by two scattering mechanisms: (i) re-illumination of the holes by the in-plane SPP radiation and (ii) an effective impedance depending on the single-hole response. The conditions for constructive and destructive interference only depend on the phase difference provided by each of the two scattering mechanisms.

Correlation of optical properties with the fractal microstructure of black molybdenum coatings

Coating is commonly used for improving the optical properties of surfaces for solar collector applications. The coating morphology depends on the deposition conditions, and this determines the final optical characteristics. Coating morphologies are irregular and of fractal nature, so a suitable approach for its characterization should use methods borrowed from fractal analysis. The aim of this work is to study the fractal characteristics of black molybdenum coatings on copper and to relate the fractal parameters to the optical properties. To this end, coating surfaces were prepared via immersion in a solution of ammonium paramolybdate for different deposition periods. The fractal analysis was carried out for SEM and AFM images of the coating surface and the fractal properties were obtained with a recently developed high-dimensional extension of the well-known detrended fluctuation analysis (DFA). The most salient parameter drawn from the application of the DFA is the Hurst index, a parameter related to the roughness of the coating surface, and the multifractality index, which is related to the non-linearity features of the coating morphology. The results showed that optical properties, including absorptance and emittance, are decreasing functions of the Hurst and multifractality indices. This suggests that coating surfaces with high absorptance and emittance values are related to complex coating morphologies conformed within a non-linear structure.

Development of a model for calculating the longwave optical properties and surface temperature of a curved venetian blind

This article is about the development of a mathematical model for calculating the longwave optical properties of a curved venetian blind. The calculated optical properties are used to determine the performance of the glass window installed with a venetian blind in terms of thermal comfort. The blind, whose optical properties are considered nonspecular, is modeled as an effective layer. The effect of slat curvature is included in the developed model. A six surface enclosure formed by two consecutive slats is used to analyze for the longwave optical properties of the effective layer. The longwave optical properties, transmittance, reflectance, absorptance and emittance are developed by using the radiosity method. The steady state energy balance method along with the developed longwave optical properties are used to determine the surface temperature of the effective layer. The empirical expression for the total heat flux from the indoor glass window surface with an adjacent venetian blind is adopted in the developed model. The surface temperature of the blind, which is the key parameter for calculating the thermal performance of glass windows with venetian blinds with respect to thermal comfort, is chosen as the parameter used for the model validation. The predicted surface temperature of the venetian blind is compared with the surface temperature of the venetian blind obtained from the measurement. The agreement between the predicted temperature and the measured temperature is good.

Composition, structure and morphology of oxide layers formed on austenitic stainless steel by oxygen plasma immersion ion implantation

Oxygen ions were implanted in to austenitic stainless steel by plasma immersion ion implantation at 400°C. The implanted samples were characterized by XPS, GIXRD, micro-Raman, AFM, optical and scanning electron microscopies. XPS studies showed the presence of Fe in elemental, as Fe2+ in oxide form and as Fe3+ in the form of oxyhydroxides in the substrate. Iron was present in the oxidation states of Fe2+ and Fe3+ in the implanted samples. Cr and Mn were present as Cr3+ and Mn2+, respectively, in both the substrate and implanted samples. Nickel remained unaffected by implantation. GIXRD and micro-Raman studies showed the oxide to be a mixture of spinel and corundum structures. Optical and AFM images showed an island structure on underlying oxide. This island structure was preserved at different thicknesses. Further, near the grain boundaries more oxide growth was found. This is explained on the basis of faster diffusion of oxygen in the grain boundary regions. Measurement of total hemispherical optical aborptance, α and emittance, ɛ of the implanted sample show that it has good solar selective properties.

Parameterization of the radiative properties of midlatitude high and middle level clouds

The clouds of the middle and upper troposphere are difficult to treat in models because of their variable optical properties. Based on extensive cirrus, altostratus, and altocumulus cloud remote sensing measurements and model simulations, we offer parameterizations of visible optical depth and infrared layer emittance as functions of both cloud temperature and vertical thickness to facilitate climate modeling research. We find significant differences in the emittance relations that depend on cloud phase, but quite similar optical depth versus emittance relations. In comparison to previous midlatitude cirrus results, our findings lead to lower atmospheric heating rates.

All-solid-state electrochromic reflectance device for emittance modulation in the far-infrared spectral region

All-solid-state electrochromic reflectance devices for thermal emittance modulation were designed for operation in the spectral region from mid- to far-infrared wavelengths (2–40 μm). All device constituent layers were grown by magnetron sputtering. The electrochromic (polycrystalline WO3), ion conductor (Ta2O5), and Li+ ion-storage layer (amorphous WO3), optimized for their infrared (IR) optical thicknesses, are sandwiched between a highly IR reflecting Al mirror, and a 90% IR transmissive Al grid top electrode, thereby meeting the requirements for a reversible Li+ ion insertion electrochromic device to operate within the 300 K blackbody emission range. Multicycle optical switching and emittance modulation is demonstrated. The measured change in emissivity of the device is to 20%.

Physics design and scaling of recirculating induction accelerators: from benchtop prototypes to drivers

Recirculating induction accelerators (recirculators) have been investigated as possible drivers for inertial fusion energy production because of their potential cost advantage over linear induction accelerators. Point designs were obtained by Barnard et al. (UCRL-LR-108095, 1991; Phys. Fluids B Plasma Phys. 5 (1993), 2698) and many of the critical physics and technology issues that would need to be addressed were detailed. A collaboration (Friedman et al., 32–33 (1996) 235) involving Lawrence Livermore National Laboratory and Lawrence Berkeley National Laboratory researchers is now developing a small prototype recirculator in order to demonstrate an understanding of nearly all the critical beam dynamics issues that have been raised by Barnard et al. and subsequently. We review the design equations for recirculators (which have been incorporated into a MATHEMATICA-based design code) and demonstrate how, by keeping crucial dimensionless quantities constant, a small prototype recirculator was designed which will simulate the essential beam physics of a driver. We further show how important physical quantities such as the sensitivity to errors of optical elements (in both field strength and placement), insertion-extraction, vacuum requirements and emittance growth scale from small prototype to driver-size accelerator.

Simulation study of the remote sensing of optical and microphysical properties of cirrus clouds from satellite IR measurements

Improved ray-optics theory and Mie theory for single scattering and an adding-doubling method for multiple scattering have been used to study the interaction of radiation in NASA's Visible and Infrared Spin-Scan Radiometer Atmospheric Sounder Satellite (VAS) IR channels and the microphysics of inhomogeneous cirrus clouds. The simulation study shows that crystal shape has remarkable effects on scattering and on the radiative-transfer properties of cirrus clouds in IR spectra. The sensitivity of the brightness temperature, as observed with VAS-IR channels, to the hexagonal columns and plates in cirrus clouds is noticeable. A method that permits one to infer the optical thickness, crystal shape, ice-water content,and emittance of cirrus clouds by using a multi-IR window channel with a scanning observation technique is developed. Detailed error analyses are carried out, and the characteristics of VAS-IR window channels are investigated through the examination of the effects of sea-surface reflection and variations in the temperature and water-vapor profiles on the VAS measurements. It is shown that these effects are large and need to be considered. Some uncertainties that have risen from the theoretical model are studied; they demonstrate that the Mie-scattering theory should not be used to retrieve the microphysical and optical properties of cirrus clouds. A suitable cloud-microphysics model and a suitable scattering model are needed instead.

Optical transition radiation interferometry and beam emittance measurements

Optical transition radiation (OTR) patterns were measured using transparent foil and mirror Wartski interferometers. Electron beam divergence and profile were determined by comparing theoretically calculated OTR patterns and experimental data. The Naval Postgraduate School electron linear accelerator was determined to have a horizontal normalized emittance of (305 ± 45)π mm mrad and a vertical normalized emittance of (170 ± 25) π mm mrad. A comparison of interference patterns made with 0.5 and 5.0 μm clear nitrocellulose foils indicates that radiation produced at the three vacuum-media interfaces was coherent in the case of the thinner foil.

Wave-Optical Property of Undulator Radiation and Its Effect on Grating Monochromators

The wave-optical description of undulator radiation is presented based on a virtual grating model. It is shown that the optical emittance of the coherent part of the radiation is roughly equal to the minimum emittance defined by the uncertainty principle of light. Some discussion is presented about the emittance matching between undulator radiation and grating monochromators.

Optical and electrical properties of ion-beam-textured Kapton and Teflon

An electron bombardment argon ion source was used to ion etch polyimide (Kapton) and fluorinated ethylene propylene, FEP (Teflon). Samples of polyimide and FEP were exposed to 0.5–1.0-keV Ar ions at ion current densities of 1.0–1.8 mA/cm2 for various exposure times. Changes in the optical and electrical properties of the samples were used to characterize the exposure. Spectral reflectance and transmitance measurements were made between 0.33 and 2.6 μm using an integrating sphere after each exposure. From these measurements, values of solar absorptance were obtained. Total emittance measurements were also recorded for some samples. Surface resitivity was used to determine changes in the electrical conductivity of the etched samples. A scanning electron microscope was used to record surface structure after exposure. Presented in the paper are spectral optical data, resistivity measurements, calculated absorptance and emittance measurements, along with photomicrographs of the surface for the various exposures to Ar ions.