An in-situ real-time study on solid phase formation and its degree of structural disorder could shed light on the mechanisms of solidification from the liquid and allow insight into the creation of materials designed to possess enhanced properties and facilitate their production and application. The implementation of a Rapid Scan technique on a FT-IR emissometer designed to allow the observation of materials under extreme temperature conditions allows following the liquid to solid-state phase transition mechanisms through time-resolved emissivity spectra acquired at a speed of 20 spectra per second. The cooling rate of the material can be modified by controlling the laser-heating system. This technique has been validated on SrAl2Si2O8 feldspar, a material which displays structural disorder. The technique is sufficiently accurate to determine small changes in the linewidths of spectra obtained at different cooling rates, suggesting that structural order is increased at slower cooling speeds and confirming the Al/Si ordering dependence on thermal history.

Complex refractive indices of micrometric aluminosilicate fibers and of silica aerogel, components of a biphasic and semi-transparent material, were identified in the mid-infrared range from 295 to 1350 K. The identification was carried out by successive applications of a methodology combining infrared spectroscopy (FTIR), X-ray microtomography and Monte Carlo Ray Tracing. This identification technique proves to be an interesting tool for material design since it is now possible to forecast the radiative properties of heterogeneous and semi-transparent materials composed of identical microphases but involving different proportions and spatial distributions. With this approach, it is no longer necessary to identify effective indices or perform systematic FTIR spectroscopy measurements to get a first overview of the radiative properties of a new spatial layout of the microphases.

Emissivity spectra of amorphous silica have been acquired in a wide range of temperatures: from 4 K to more than 2500 K in static isothermal conditions, and from 2500 K to 600 K in kinetic free-cooling conditions. A fitting procedure allows extracting the temperature dependence of the dielectric function in the range of vibrational frequencies. Both sets of data are equivalent for a quantitative study of the structure of this model glass, despite the lower resolution and signal-to-noise ratio of the rapid-scan measurements. The results present clear changes at a special temperature near the α→β transition temperature for crystalline quartz. Similarly, simple relations between the intensities of the modes are found at the glass transition. This study provides insight into the structure and dynamics of vitreous silica at high temperature and proves that rapid-scan infrared emission spectroscopy is a viable analytical technique for the study of materials in non-equilibrium conditions.

The real-time observation of molten materials and their cooling to solid state is of importance for many industrial processes. In this work, we describe additional possibilities obtained by the implementation of a Rapid Scan technique on an FT-IR emissometer designed to allow the observation of materials under extreme temperature conditions. The possibility of following liquid-to-solid state phase transition mechanisms through time-resolved emissivity will be illustrated. This new methodology presents interesting possibilities for the study of structural transformations through the real-time monitoring of the dielectric function and true sample temperature of the experimental emissivity spectra acquired every 50 ms under free cooling conditions.

Using an emittance technique with a fast CO2 laser heating of glass samples, the high-temperature absorption spectra in the near-infrared region of ultrapure and colored (Co-, Cu-, Mn-, and Ni-doped) glasses are measured. The effects of higher glass temperatures on these absorption spectra are explained in the framework of the ligand field theory. Thus, the temperature-dependent absorption bands of the previous transition metal ions are assigned to electronic transitions among the ligand field energy levels of these ions. In particular, spectral shifts, spectral broadening, and changes in absorption strength are ascribed to changes in the structural symmetry of the ionic sites in the glass matrix and to changes of the ligand field strength at increasing temperatures. Besides, the temperature-dependent Rosseland mean absorptions of the sulfate fined soda lime silicate glass melts, colored with the previous transition metal ions, are derived from the absorption spectra. Combining all the data, semiempirical correlations are derived, which predict the Rosseland thermal radiation properties as a function of glass temperature and of glass redox chemistry. The latter property involves the temperature-dependent concentration of the specific valency of the coloring ions, determined independently, e.g. by a Gibbs minimization redox calculation tool.

A new methodology was developed to identify the spectral complex refractive index of semi-transparent solid phases within heterogeneous media up to high temperatures. In this methodology, numerical sam-ples are first generated from statistical information about the microstructure of a given material obtained by X-ray micro-tomography. The radiative properties of these numerical samples (reflectance, transmit-tance, and emittance) are then simulated with a Geometric Monte Carlo Ray Tracing code while the radiative properties of the real material are measured by Fourier Transform Infrared spectroscopy. The spectral complex refractive index is then extracted thanks to an optimization algorithm, by minimizing the discrepancies between the experimental and numerical radiative properties. This methodology was applied to a fibrous sample made of pure silica. The complex index was extracted at 295 K and 1010 K. In both cases, it enabled a good prediction of the radiative properties of the material and proved the relevance of performing calculations with characteristics identified at the local scale instead of the bulk ones.(c) 2023 Elsevier Ltd. All rights reserved.

Near-field thermal emission largely exceeds blackbody radiation, owing to spectrally sharp emission in surface polaritons. We turn the Casimir-Polder interaction between Cs(7P_{1/2}) and a sapphire interface into a sensor sharply filtering, at 24.687 THz, the near-field sapphire emission at ∼24.5  THz. The temperature evolution of the sapphire mode is demonstrated. The Cs sensor, sensitive to both dispersion and dissipation, suggests the polariton to be redshifted and sharper, as compared, up to 1100 K, to predictions from far-field sapphire emission, affected by birefringence and multiple resonances.

The primary scientific goal of ICARUS (Investigation of Coronal AcceleRation and heating of solar wind Up to the Sun), a mother-daughter satellite mission, proposed in response to the ESA "Voyage 2050" Call, will be to determine how the magnetic field and plasma dynamics in the outer solar atmosphere give rise to the corona, the solar wind, and the entire heliosphere. Reaching this goal will be a Rosetta Stone step, with results that are broadly applicable within the fields of space plasma physics and astrophysics. Within ESA's Cosmic Vision roadmap, these science goals address Theme 2: "How does the Solar System work?" by investigating basic processes occurring "From the Sun to the edge of the Solar System". ICARUS will not only advance our understanding of the plasma environment around our Sun, but also of the numerous magnetically active stars with hot plasma coronae. ICARUS I will perform the first direct in situ measurements of electromagnetic fields, particle acceleration, wave activity, energy distribution, and flows directly in the regions in which the solar wind emerges from the coronal plasma. ICARUS I will have a perihelion altitude of 1 solar radius and will cross the region where the major energy deposition occurs. The polar orbit of ICARUS I will enable crossing the regions where both the fast and slow winds are generated. It will probe the local characteristics of the plasma and provide unique information about the physical processes involved in the creation of the solar wind. ICARUS II will observe this region using remote-sensing instruments, providing simultaneous, contextual information about regions crossed by ICARUS I and the solar atmosphere below as observed by solar telescopes. It will thus provide bridges for understanding the magnetic links between the heliosphere and the solar atmosphere. Such information is crucial to our understanding of the plasma physics and electrodynamics of the solar atmosphere. ICARUS II will also play a very important relay role, enabling the radio-link with ICARUS I. It will receive, collect, and store information transmitted from ICARUS I during its closest approach to the Sun. It will also perform preliminary data processing before transmitting it to Earth. Performing such unique in situ observations in the area where presumably hazardous solar energetic particles are energized, ICARUS will provide fundamental advances in our capabilities to monitor and forecast the space radiation environment. Therefore, the results from the ICARUS mission will be extremely crucial for future space explorations, especially for long-term crewed space missions.

Experimental high temperature near infrared (NIR) absorption spectra of different SiO2-based glasses, including lead silicate crystal glass, clear soda lime silicate (SLS) glass and fused silica with low and high OH content, are compared. The more polarizable the glass, the stronger is the increase in the high temperature NIR absorption at wavelengths < 2 mu m, involving a red shift of the optical bandgap edge with increasing temperature. It appears that the modified glassy Urbach's rule provides a framework for describing the temperature red shift of the absorption edge of lead silicate crystal glass, even above T-g. This red shift causes a 4-7 times lower Rosseland thermal radiation conductivity of lead crystal glass melts compared to clear SLS glass melts. Low OH fused silica is practically transparent for NIR thermal radiation, also at high temperatures above T-g. Incorporation of water in fused silica increases the NIR absorption in the spectral region 1.7-3.4 mu m, for all temperatures. An upper limit of the diffusion coefficient D of water in fused silica was estimated from the time to measure the high temperature NIR spectra of thin (similar to 2 mm) samples: D < 4 * 10(-10) m(2)/s at temperatures up to around 2000 degrees C.

A new methodology allowing real time observation of materials during their cooling, from the molten state to low temperature has been developed. This possibility originates from the implementation of a Rapid Scan feature on a FT-IR emissometer designed to probe materials submitted to extreme temperature conditions. Original time-resolved emissivity dependence during the phase transition are reported for the first time. The resulting out of equilibrium, dynamic, new data have been compared to the equilibrium, static, classical measurements to demonstrate the reliability of the new technique on two reference samples (Al2O3 and SiO2). The proposed method has high possibilities to be applied to different materials to enable the observation of fast structural transformations during liquid to solid phase change through the evolution of the dielectric function.

The rheology and thermodynamical evolution of magma, either in reservoirs, conduits, or at the surface, are governed by temperature. To determine the field temperature, remote-sensing methods based on measuring the infrared radiance are widely applied, but they are subject to assumptions and caveats that can propagate into large uncertainties. This is related to the poor knowledge of one of the most critical parameters, namely the spectral emissivity. In this work, we aim at filling this gap through in situ spectral emissivity measurements performed over wide temperature (700–1600 K) and spectral ranges (1.25– $25~\mu \text{m}$ ) on two representative phonolitic compositions from Erebus (Antartica) and Teide (Spain) volcanoes. The laboratory spectra allow to determine precisely spectral emissivity in the thermal infrared (TIR), middle infrared (MIR), and shortwave infrared (SWIR) ranges. The results reveal the complexity and contrasted behavior of the radiative properties of the two rocks melts, despite their broadly similar composition. The spectral emissivity varies significantly as a function of temperature, composition, crystallinity, thickness, and thermal history. Altogether, the data reveal that emissivity cannot be considered as a constant value and question previous arguments that active lava always has lower emissivity than frozen lava. Finally, the laboratory-measured values of spectral emissivity were used to refine the temperature of Erebus lava lake gathered from previous remote-sensing methods.

Near-field thermal exchanges, dramatically differing from blackbody equilibrium, are enhanced by surface mode emission. We probe the features of the spectrally narrow thermal sapphire surface emission up to 1100 K, through atom surface Casimir-Polder interaction.

The effective refractive index (neff) of suspensions of subwavelength particles is calculated in resonant domains of the thermal infrared region. On account of strong cooperative effects, notable deviations arise from what is expected for small particles; these features include unusual activation of higher‐order multipoles despite the fact that the system can be homogenized and the manifestation of effective magnetic properties. The former feature leads to fundamental questions about the validity of the homogenization procedure, in particular regarding the meaning of the imaginary part of neff, that is absorption by the particles and therefore interrogates the degree to which the composite can be unrestrictedly described by an effective dielectric function. The latter feature offers interesting perspectives for the development of nanophotonic devices, based on dielectric subwavelength particles, exhibiting an effective magnetic response. Finally, the study of the coherent and incoherent decomposition of the field allows to demonstrate, counterintuitively, that a material can admit effective optical properties even in the presence of strong incoherent intensities and that the variance of the field over a statistical ensemble of configurations is a misleading indicator of scattering.

An innovative technique was developed for the direct measurement of the absolute radiant flux emitted from transient flames. The design of the experimental device, called FAIRS (Fast Absolute Infra-Red Sensor), is detailed in this work. The main concept of FAIRS is based on the combination of a carbon nano-tube-based black body as a sensitive element, coupled to a fast IR HgCdTe detector via an achromatic optical setup. A specific calibration protocol based on a laboratory blackbody (ambient to 850 °C) allows the qualification of the FAIRS for absolute radiative heat-flux measurements, with a response time less than 1 µs that was checked, thanks to pulsed laser irradiation. It is thus demonstrated that FAIRS is a good candidate for transient measurements, with a simplified calibration procedure. FAIRS was coupled with ultra-fast schlieren imaging on spherical expanding CH4/air and C3H8/air flames. In this condition, it is possible to correlate the real time flame diameter to its absolute radiative heat losses.

The dielectric function of a cerium oxide nanopowder has been investigated by infrared spectroscopy. The use of Bergman's spectral representation and a semi-quantum dielectric function model allows an accurate retrieval of the main features of the lattice dynamics of this nanocompound. Due to the absence of significant lattice strain or vacancy concentration, the observed differences between the dielectric functions of the nanopowder and a single crystal can be explained mainly by the phenomenon of phonon confinement. The results are validated by comparison to literature data and additional spectroscopic techniques, as well as by direct measurements of powder filling factors.

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. (C) 2021 Elsevier Ltd. All rights reserved.