Showing papers in "Journal of Quantitative Spectroscopy & Radiative Transfer in 2021"
TL;DR: This work proposes a novel machine learning algorithm based on physics informed neural networks (PINNs), which are trained by minimizing the residual of the underlying radiative tranfer equations to simulating radiative transfer efficiently.
Abstract: We propose a novel machine learning algorithm for simulating radiative transfer. Our algorithm is based on physics informed neural networks (PINNs), which are trained by minimizing the residual of the underlying radiative transfer equations. We present extensive experiments and theoretical error estimates to demonstrate that PINNs provide a very easy to implement, fast, robust and accurate method for simulating radiative transfer. We also present a PINN based algorithm for simulating inverse problems for radiative transfer efficiently.
66 citations
TL;DR: In this article, a magnetophotonic crystal was proposed to realize strong non-reciprocal radiation at small angles, and the numerical results showed that strong nonreciprocity can be obtained at angle of incidence of 30o, which is much smaller than the typical angle of 60°.
Abstract: Kirchhoff's law plays a vital role in radiation heat transfer, which has been recently generalized to hold for both reciprocal and nonreciprocal materials. However, the verification of the generalized Kirchhoff's law for nonreciprocal materials in experiment has not been reported. Previous proposed structures could only obtain strong nonreciprocal radiation at large angles, which were not favorable in experiment. Here, we proposed magnetophotonic crystal to realize strong nonreciprocal radiation at small angles. The numerical results show that strong nonreciprocal radiation can be obtained at angle of incidence of 30o, which is much smaller than the typical angle of 60°. The distribution of magnetic field is used to reveal the mechanism, and it indicates that the enhanced nonreciprocity is attributed to the excitation of Tamm plasmon polaritons. We believe such magnetophotonic crystal is promising in verifying the Kirchhoff's law for nonreciprocal materials.
36 citations
TL;DR: In this article, the authors investigated the NFRHT between two hexagonal boron nitride (hBN) slabs considering the role of HVPPs and HSPPs.
Abstract: It has been found that near-field radiative heat transfer (NFRHT) between hyperbolic media, such as hexagonal boron nitride (hBN), can be significantly enhanced due to excitation of hyperbolic volume phonon polaritons (HVPPs) and hyperbolic surface phonon polaritons (HSPPs). However, the role of HVPPs and HSPPs in type I and type II hyperbolic bands has rarely been discussed in depth. In this paper, we investigate the NFRHT between two hBN slabs considering the role of HVPPs and HSPPs. The theoretical analysis and numerical results show that when the optical axis is perpendicular to the material surface, the enhanced NFRHT is attributed to the excitation of HVPPs in both type I and type II hyperbolic bands, while HSPPs cannot be excited in this case. When the optical axis is parallel to the material surface, only HVPPs can be excited in type I hyperbolic band, while both HVPPs and HSPPs can be excited in type II hyperbolic band. In addition, the effect of the slab thickness on the dispersion relations of HVPPs and HSPPs, and on the enhancement of NFRHT is also studied. We believe the results in this paper could help to elucidate the mechanisms and manipulation of enhanced NFRHT between uniaxial hyperbolic materials.
31 citations
TL;DR: In this article, the authors investigated slow light effect and magnetic polaritons, and analyzed other physical model coupling mechanisms in photonic crystals to construct a class of two-dimensional layers of Ni-Al2O3 as a pyramid array solar energy absorber.
Abstract: Efficient absorption of solar spectral radiation is a key requirement in solar heat utilization. In an effort to achieve this goal, this study investigated slow light effect and magnetic polaritons, and analyzed other physical model coupling mechanisms in photonic crystals. To construct a class of two-dimensional layers of Ni-Al2O3 as a pyramid array solar energy absorber, the high melting points of Ni and Al2O3 were utilized to create an arrangement of absorbers with good thermal stability, low sensitivity to angle of incidence, and polarization independence. Based on AM1.5 solar spectral data, a simulation study of the photothermal absorption characteristics of this type of absorber in the 0.3–2.5 µm band was conducted. The results showed that the photothermal conversion efficiency is as high as 96.45%. Compared with the traditional single physical effect design, the conversion efficiency of this photonic crystal structure is increased by ~11%. Furthermore, increasing the concentration factor allows the absorber to maintain high efficiency even at high temperatures, which provides theoretical evidence for the efficient use of solar radiation. This work will be beneficial in several areas, including solar thermal utilization, thermal photovoltaics, absorber design, and radiator design in radiant refrigeration systems.
29 citations
TL;DR: In this paper, a model, named Weighted Sum of Gray Soot Fractal Aggregates (WSGSA), was proposed to calculate the radiative properties of nongray soot fractal aggregates in gas-soot mixture by combining the features of full-spectrum k-distribution model and Weighted-Sum-of-Gray-Gases (WSGG) model.
Abstract: Soot, a product of insufficient combustion, is usually in the form of aggregate. The multi-scattering of soot fractal aggregates has been proved to play an important role in studying the soot radiative properties, which is rarely considered in predicting the radiative heat transfer in combustion flame. In the present study, based on the Rayleigh-Debey-Gans-Fractal-Aggregate (RDG-FA) theory, a model, named Weighted Sum of Gray Soot fractal Aggregates (WSGSA), used to calculate the radiative properties of nongray soot fractal aggregates in gas-soot mixture is developed by combining the features of full-spectrum k-distribution (FSK) model and Weighted-Sum-of-Gray-Gases (WSGG) model. Four gray soot fractal aggregates obtained from reordering in the form of the k-distribution at Gauss-Legendre integral points are selected to represent the nongray soot fractal aggregate, while corresponding weighting factors are obtained by fitting the radiation data obtained by the line-by-line (LBL) model with soot radiation data. Then, the WSGSA model is systematically validated by studying the radiative heat transfer properties in a one-dimensional plane-parallel slab system only with soot aggregates. The maximum relative discrepancies of emittance under different temperatures and different path lengths are less than 12%, while the maximum relative discrepancies of radiative heat source term and radiative heat flux are both less than 11% with path length less than 3 m. Moreover, combined with the WSGG model, the performance of the WSGSA model is further validated by predicting the radiative heat transfer properties in the mixture consisted of gases and soot aggregates, and acceptable results are also obtained. All the results reveal that the developed model can be applied to predict the radiative heat transfer in the mixture containing gases and soot aggregates, even in the case of significant changes in temperature and species concentration.
28 citations
TL;DR: In this paper, total internal partition sums (TIPS) are reported for the 181 isotopologues of 57 molecules important in planetary atmospheres, with the exception of #34 atomic oxygen.
Abstract: Total internal partition sums (TIPS) are reported for the 181 isotopologues of 57 molecules important in planetary atmospheres. Molecules 1 to 55, with the exception of #34 atomic oxygen, are taken from the HITRAN2020 list, and for some molecules additional isotopologues are considered. Molecules 56 and 57 are C3H4, CH3, respectively. New to TIPS are the calculations for 12CH4, 13CH4, 12CH3D, 13CH3D, 14N16O, 15N16O, 14N18O, 16O32S18O, 33S16O2, 15N16O2, 18OH, 16OD, 35Cl16O, 37Cl16O, 16O13C34S, 32S19F6, 12C2H5D, 12C2H3D, 12C19F4, 12CH319F, 70GeH4, 72GeH4, 73GeH4, 74GeH4, 76GeH4, 12CH3127I, 13CH3127I, and 14N19F3. In addition, all the molecules/isotopologues that were not recalculated for TIPS2017 (Gamache et al., JQSRT 203, 70, 2017) have been recalculated using the 2014 CODATA physical constants. The TIPS are determined by various methods, generally from 1 to 5000 K. These data are provided with HITRAN2020 and a new version of the TIPS code is available in both FORTRAN and python languages.
26 citations
TL;DR: In this paper, the role of the one-dimensional photonic crystals as an anti-reflecting coating and back reflector to improve the optical properties of amorphous silicon solar cells was theoretically demonstrated.
Abstract: In recent times, solar cell presents a good candidate for solving the problems of energy crisis and environmental pollution as well. However, it could suffer from the limited absorption among the full spectral wavelength. In this context, we present in this paper a simple and efficient design towards a prominent enhancement of the optical characteristics of amorphous silicon solar cells. Here, we have theoretically demonstrated the role of the one-dimensional photonic crystals as an anti-reflecting coating and back reflector to improve the absorption properties of the proposed cell. The anti-reflecting coating is designed from a single period of the one-dimensional quadrant photonic crystals. Whilst 10 periods of the one dimensional binary photonic crystals are used to design the back reflecting mirror. The theoretical framework of our study is mainly based on the finite element method and the transfer matrix method as well. The investigated results verify the significant role of the anti-reflecting coating and the back mirror in raising the absorption values of the cell that could reach over than 0.9 in the wavelength domain from 350 nm to 640 nm. Moreover, the change in the values of the angle of incidence investigates a distinct decrease in spectral absorption.
24 citations
TL;DR: In this article, a free and freely available computer program (0nset) is developed to determine the inflection point and subsequent x-intercept defining λ onset, and numerically computed results from 0nset are independent of application bias.
Abstract: Human attribution of absorption onset wavelength ( λ onset ) most often produces small, but non-negligible errors in the attribution of this value tied to the optical energy gap. The present work utilizes a free and freely available computer program (“0nset”) developed herein to determine the inflection point and subsequent x-intercept defining λ onset . The manually attributed absorption curve λ onset wavelengths are typically in error to the red (in 27 out of 38 attributions) for the dataset utilized in the present work when a rigorous manual analysis was performed implying a systematic human error. The raw ( − 2 nm) and absolute (3 nm) errors are relatively small, but there are exceptions when the errors are even larger than 20 nm. The numerically computed results from 0nset are independent of application bias and will reduce errors moving forward by consistently generating λ onset values from the same algorithm. Additionally, it will reduce errors in circumstances where the inflection points are difficult to isolate or in regions like the UV where ∼ 5–10 nm errors are more significant energetically. Finally, 0nset only requires .csv inputs and is built for both Windows and Unix-based operating systems making uptake and usage straightforward for experimental groups.
23 citations
TL;DR: In this paper, a novel approach to solving Chandrasekhar's problem in radiative transfer using the recently developed Theory of Functional Connections is presented, which is designed to elegantly and accurately solve the Linear Boundary Value Problem from the angular discretization of the integrodifferential Boltzmann equation for Radiative Transfer.
Abstract: We present a novel approach to solving Chandrasekhar’s problem in radiative transfer using the recently developed Theory of Functional Connections. The method is designed to elegantly and accurately solve the Linear Boundary Value Problem from the angular discretization of the integrodifferential Boltzmann equation for Radiative Transfer. The proposed algorithm falls under the category of numerical methods for the solution of radiative transfer equations. This new method’s accuracy is tested via comparison with the published benchmarks for Mie and Haze L scattering laws.
21 citations
TL;DR: In this article, the extinction and backscattering properties of the aerosol particles in the lidar beam are investigated and a review of different ways to measure aerosol-particle extinction is presented.
Abstract: Elastic backscatter lidar is an established method useful to characterize the particles forming an atmospheric aerosol. Fundamental to lidar measurements are the extinction and backscattering properties of the aerosol particles in the lidar beam. This review aims to give the reader an understanding for how lidar measurements are made, modeled, and applied. Specific emphasis is placed on extinction, which manifests attenuation of the lidar beam by the aerosol, and the backscattering that ultimately constitutes the measured signal. The so-called lidar equation, which quantifies this signal in terms of aerosol-particle properties, is derived from radiative transfer theory. Extinction is examined in terms of the redistribution of energy from the lidar beam by the particles and is shown to be inherently linked to interference between the incident and scattered light. Ways to measure aerosol-particle extinction are reviewed, including a recent method where the wave interference constitutes a digital hologram that may be processed to yield both the cross section and an image of the particle. The semi-graphical method of phasor analysis is also presented and used to reveal connections between the scattering characteristics of a particle and the distribution of electric field within it. Finally, a recently developed elastic backscatter lidar system, Colibri, is described and an example of its measurement capabilities are presented.
19 citations
TL;DR: In this article, the authors carried out a comparative analysis of planar metallic, high refractive index dielectric, and hybrid nanoantennas considering three different parameters: the Purcell factor enhancement, radiation efficiency, and directionality properties.
Abstract: The confinement of electromagnetic energy to subwavelength volumes through nanoscale antennas can be used to enhance the spontaneous emission of quantum emitters. With this aim, different configurations of metallic and high refractive index dielectric nanoparticles have been explored. Here, we carry out a comparative analysis of planar metallic, high refractive index dielectric, and hybrid nanoantennas considering three different parameters: the Purcell factor enhancement, radiation efficiency, and directionality properties. We focus our study on different geometries and material combinations of a dimer of cylinders. A dimer made of two gold nanocylinders is the most promising candidate for improving the spontaneous emission. While most previous works have paid attention to the redirection of the scattered emission in the nanoparticle plane, our proposed nanostructure of two large gold cylinders ( R = λ / 4 ) emits most of the radiation upwards. This effect is due to the strong quadrupolar electric contribution to the resonant mode. With the aim to further improve the directionality properties, additional silicon nanocylinders are used as directors of the scattered radiation, increasing the directivity by a factor of 2.4 with respect to the gold dimer without directors. All in all, a hybrid structure composed of a gold dimer and silicon nanoparticles is proposed to enhance the spontaneous emission of a single quantum dot and to govern its emission pattern. The results shown in this work could be useful in fluorescence enhancement or in quantum photonics. They are particularly interesting for the development of single-photon sources based on quantum dots and other nanoscale emitters.
TL;DR: The spectral line weighted-sum-of-gray-gases (SLW) method as mentioned in this paper is a global spectral method based on a spectral reordering concept, while the latter uses spectral binning.
Abstract: Both the full-spectrum k-distribution (FSK) method and the spectral line weighted-sum-of-gray-gases (SLW) method are global spectral methods, with the former based on a spectral reordering concept, while the latter uses spectral binning. Both can provide excellent accuracy with outstanding numerical efficiency to model radiative heat transfer in combustion gases. In the present paper we aim to complete the development of both methods, and to tie them together, pointing out their commonalities and differences of their nonhomogeneous media extensions, employing either the correlated or scaled absorption coefficient assumption. Results from the complete set of plausible implementations are discussed and compared in detail for several radiative heat transfer calculations carried out in both 1D slabs and a real combustion field. The results show that emission is an important criterion to examine the accuracy of global methods applied to nonhomogeneous media, i.e., those that preserve emission generally give more accurate results than those that do not. It was also found that, while proper choice of the reference temperature required by all methods is important, the recommended methods appear to be only weakly dependent on that choice. Finally, equivalent SLW schemes are generally somewhat less accurate than their FSK counterparts due to their low-order spectral integration scheme; and this may be exacerbated if full-spectrum k-distributions are determined by mixing of values from individual species, as appears to be the preferred approach by SLW users to date.
TL;DR: In this article, a line-by-line spectroscopic database with beyond-Voigt line-shape parameters (broadening and shift, their speed dependence, and complex Dicke parameter) is presented.
Abstract: We demonstrate a new method for populating line-by-line spectroscopic databases with beyond-Voigt line-shape parameters, which is based on ab initio quantum scattering calculations. We report a comprehensive dataset for the benchmark system of He-perturbed H2 (we cover all the rovibrational bands that are present in the HITRAN spectroscopic database). We generate the entire dataset of the line-shape parameters (broadening and shift, their speed dependence, and the complex Dicke parameter) from fully ab initio quantum-scattering calculations. We extend the previous calculations by taking into account the centrifugal distortion for all the bands and by including the hot bands. The results are projected on a simple structure of the quadratic speed-dependent hard-collision profile. We report a simple and compact formula that allows the speed-dependence parameters to be calculated directly from the generalized spectroscopic cross sections. For each line and each line-shape parameter, we provide a full temperature dependence within the double-power-law (DPL) representation, which makes the dataset compatible with the HITRAN database. The temperature dependences cover the range from 20 to 1000 K, which includes the low temperatures relevant for the studies of the atmospheres of giant planets. The final outcome from our dataset is validated on highly accurate experimental spectra collected with cavity ring-down spectrometers. The methodology can be applied to many other molecular species important for atmospheric and planetary studies.
TL;DR: In this paper, the authors collected the Sahara-OSN and Gobi-Beijing desert dust samples with the help of the Ramon y Cajal Program of the Spanish Ministry of Science and Innovation (RYC-2016-19570).
Abstract: This work has been funded by the excellence research program of the Andalusian Regional Government, grant number P18RT-1854, the National Plan of Scientific and Technical Research and Innovation of the Spanish Ministry of Science and Innovation, grant number RTI2018-095330-B-100 (LEONIDAS), and the "Center of Excellence Severo Ochoa" award to the Instituto de Astrofisica de Andalucia (SEV-2017-0709) by the Spanish State Agency for Research. J.C.G.M acknowledges financial support from the Ramon y Cajal Program of the Spanish Ministry of Science and Innovation (RYC-2016-19570). JoseLuis de la Rosa, JoseAntonio Ruiz and Shi Zongbo are acknowledged for collecting the Sahara-OSN and GobiBeijing desert dust samples.
TL;DR: In this article, a method of equation-solving RDFIEM was developed to obtain the solution of RTE in a three-dimensional (3D) anisotropic scattering medium, which can effectively avoid the stochastic ray-tracing process of the traditional RMC method and obtain the value of RDF by solving linear equations directly.
Abstract: High-directional resolution radiation intensity (RI) can provide substantial measurement information inside the participating medium, such as the distribution of temperature and physical properties. Therefore, efficiently and accurately solving the radiative transfer equation (RTE) to obtain RI in any direction is the key and challenge of target-detection and inverse-radiation problems. In our previous works [ 1 , 2 ], the integral equation method based on the radiation distribution factor (RDFIEM) was proposed to accurately obtain an arbitrary directional RI. To overcome the inefficiency of the RDFIEM in building a radiation distribution factor (RDF) database from the time-consuming reverse Monte Carlo (RMC) method, a method of equation-solving RDFIEM (ES-RDFIEM) was improved and developed to obtain the solution of RTE in a three-dimensional (3D) anisotropic scattering medium in this work, which can effectively avoid the stochastic ray-tracing process of the traditional RMC method and obtain the value of RDF by solving linear equations directly. The mathematical principles and formulae of ES-RDFIEM are introduced and deduced in detail, whose core idea is to suppose a specified element with a unit blackbody emission, whereas the remaining elements have no energy emission. Subsequently, the linear equations for the RDF, which are only concerned with the physical properties and geometric factors of the radiative system, can be constructed and solved. The computational accuracy and efficiency of ES-RDFIEM and RMC in several cases with different parameters were comprehensively compared. The results showed an excellent agreement between the RDF values and the RI calculated by the two methods. The computational efficiency of ES-RDFIEM was significantly improved compared to RMC, which was almost unaffected by radiation properties.
TL;DR: In this paper, the existence of newly additional axicon forces associated to both the usual scattering and gradient forces was demonstrated when a Rayleigh particle is illuminated by an off-axis Bessel beam.
Abstract: In two recent papers, it has been demonstrated that, beside usual scattering and optical forces, new optical forces and terms are exhibited when a Rayleigh particle is illuminated by an off-axis Bessel beam. Namely, (i) axicon optical forces are associated with scattering optical forces and (ii) additional axicon terms are associated with gradient optical forces. These extra-axicon forces and terms are zero when the axicon angle is zero and/or (most often) when an on-axis configuration is considered rather than an off-axis configuration. This study was devoted to longitudinal forces. The present paper is devoted to transverse forces and demonstrates the existence of newly additional axicon forces associated to both the usual scattering and gradient forces. Again, these new extra-axicon forces are zero when the axicon angle is zero and/or when an on-axis configuration is considered rather than an off-axis configuration.
TL;DR: SMUTHI as mentioned in this paper is a python package for the efficient and accurate simulation of electromagnetic scattering by one or multiple wavelength-scale objects in a planarly layered medium, which combines the T-matrix method for individual particle scattering with the scattering matrix formalism for the propagation of the electromagnetic field through the planar interfaces.
Abstract: SMUTHI is a python package for the efficient and accurate simulation of electromagnetic scattering by one or multiple wavelength-scale objects in a planarly layered medium. The software combines the T-matrix method for individual particle scattering with the scattering matrix formalism for the propagation of the electromagnetic field through the planar interfaces. In this article, we briefly introduce the relevant theoretical concepts and present the main features of SMUTHI. Simulation results obtained for several benchmark configurations are validated against commercial software solutions. Owing to the generality of planarly layered geometries and the availability of different particle shapes and light sources, possible applications of SMUTHI include the study of discrete random media, meta-surfaces, photonic crystals and glasses, perforated membranes and plasmonic systems, to name a few relevant examples at visible and near-visible wavelengths.
TL;DR: In this article, the propagation properties of vortex cosine-hyperbolic-Gaussian beams (vChGBs) through a strongly nonlocal nonlinear media (SNNM) are investigated theoretically based on the Snyder-Mitchell model.
Abstract: The propagation properties of vortex cosine-hyperbolic-Gaussian beams (vChGBs) through a strongly nonlocal nonlinear media (SNNM) are investigated theoretically based on the Snyder-Mitchell model. The propagation formula, the second-order intensity moment beam width and the curvature radius of an on-waist incident vChGB in SNNM are derived. The evolutions of the intensity distribution pattern, the beam width and the curvature radius during propagation in SNNM are illustrated graphically with numerical examples. It is found that the vChGBs pattern evolves periodically upon propagation and its behavior is strongly affected by the initial beam power and the beam parameters; the beam evolution is a breather-like. For a critical initial power and under specific values of the beam parameters, the beam characteristics are invariant during propagation; the vChGBs behavior is a soliton-like.
TL;DR: In this paper, a machine learning-based inverse radiation model was proposed to retrieve two-dimensional temperature, CO 2, H 2 O, and CO mole fractions of laminar flames from hyperspectral measurements.
Abstract: The latest hyperspectral measurements of combustion flames by Rhoby et al. (2014) provided extensive spatially and spectrally resolved information of flame radiation, which has been explored to retrieve two-dimensional, multi-scalar values of these flames with the conventional gradient-based optimization method. The drawback of that method is that the inverse radiation problem was solved through iterations with computationally intensive radiative heat transfer calculations and high-resolution wide-spectrum modeling, making the retrieving process very time-consuming. In the present study, we propose a machine learning based efficient inverse radiation model to retrieve two-dimensional temperature, CO 2 , H 2 O, and CO mole fractions of laminar flames from hyperspectral measurements. The model is trained with synthetic numerical data and is tested against previously made OH-laser absorption measurements and chemical equilibrium calculations for ethylene laminar flames with different equivalence ratios. The training data generation process, machine learning model architecture, model training, and validations are discussed in detail. Results have shown that the proposed machine learning based inverse radiation model is both accurate and efficient.
TL;DR: In this paper, a cavity ring down spectrometer was used to measure the water spectrum in the 12969 - 13172 cm−1 region, leading to the determination of 103 new levels and correction of 134 levels of H216O.
Abstract: The oxygen A-band near 760 nm is used to determine the air-mass along the line of sight from ground or space borne atmospheric spectra. This band is located in a spectral region of very weak absorption of water vapor. The increased requirements on the determination of the air columns make suitable to accurately characterize water absorption spectrum in the region. In the present work, we use a cavity ring down spectrometer newly developed in Tomsk, to measure with unprecedented sensitivity and accuracy the water spectrum in the 12969 - 13172 cm−1 region. While about fifty transitions were previously detected in the region, a total of about 580 water lines are measured by CRDS and rovibrationally assigned, leading to the determination of 103 new levels and correction of 134 levels of H216O. Spectroscopic line lists available in the region (HITRAN, W2020 and theoretical line lists) show some important deviations compared to observations. In particular, line intensities are poorly predicted by available ab initio calculations for transitions involving a highly bending excitation.
TL;DR: In this article, a class of exact solutions of the RTE pertaining to a uniform Lambertian illumination of any non-absorbing homogeneous and inhomogeneous volume are presented and discussed.
Abstract: In this work, special invariance properties of a class of exact solutions of the radiative transfer equation (RTE) pertaining to a uniform Lambertian illumination of any non-absorbing homogeneous and inhomogeneous volume are presented and discussed. This class of solutions of the RTE traces a reference ground under which light propagation can be studied in a special simplified regime. Despite the difficulties to obtain general solutions of the radiative transfer equation, the condition of Lambertian illumination determines a unique regime of photon transport where quite easy and simple invariant solutions can be obtained in all generality for homogeneous and inhomogeneous geometries. These solutions are invariant both with respect to the geometry (size and shape of the volume) and with respect to the scattering properties, i.e. scattering coefficient, scattering function and homogeneity of the considered domain. Another evident advantage of these solutions is that they are exact solutions known with arbitrary precision and can thus be used as reference standard for photon migration studies.
TL;DR: In this paper, an extension of the Hamiltonian of the two dimensional limit of the vibron model to encompass all possible interactions up to four-body operators is presented, which is used to model the bending spectrum of four molecules: HNC, H 2 S, Si 2 C, and NCNCS.
Abstract: We present an extension of the Hamiltonian of the two dimensional limit of the vibron model to encompass all possible interactions up to four-body operators We apply this Hamiltonian to the modeling of the bending spectrum of four molecules: HNC, H 2 S, Si 2 C, and NCNCS The selected molecular species include linear, bent, and nonrigid equilibrium structures, proving the versatility of the algebraic approach which allows for the consideration of utterly different physical cases within a single Hamiltonian and a general formalism For each case we compute predicted bending energies and wave functions, that we use to depict the associated quantum monodromy diagram, Birge-Sponer plot, and participation ratio In nonrigid cases, we also show the bending energy functional obtained using the coherent –or intrinsic– state formalism
TL;DR: In this article, a Bruker IFS 125HR Fourier transform spectrometer was used to measure pure carbon dioxide transmittance spectra in the spectral range 6000-7000 cm−1.
Abstract: A Bruker IFS 125HR Fourier-transform spectrometer has been used to measure pure carbon dioxide transmittance spectra in the spectral range 6000–7000 cm−1, including the bands 30011-00001, 30012-00001, 30013-00001, 30014-00001, and 00031-00001. A total of 10 measurements with absorption path lengths between 14.6 and 59.4 m and sample pressures from 3 to 80 mbar were performed at 295 K. A multispectrum fitting approach was used applying the Hartmann-Tran profile extended to account for line mixing in the Rosenkranz first order perturbation approximation. Line positions, self-shifts, intensities, self-broadened widths, their speed dependence and in some cases line mixing were adjusted for fitting the measurements. A rigorous error analysis has been performed. The primary goal of this work was to investigate whether Fourier transform spectroscopy can deliver line intensity accuracy down to the 0.1% level. In this work, a combined systematic standard uncertainty of 0.15% has been achieved, further improvements down to the 0.1% level are feasible. The achieved level of combined standard uncertainty has, to our knowledge, not been reached by Fourier-transform spectroscopy before. Comparisons with most recent work are presented for line positions, line intensities, self-broadening and its speed dependence, and self-shifts. Measurement and line parameter databases are provided on Zenodo (doi: 10.5281/zenodo.4525272 ).
TL;DR: In this article, the authors used a Fourier transform spectrometer based on a compact mid-infrared difference frequency generation comb source to perform broadband high-resolution measurements of nitrous oxide, 14N216O, and retrieve line center frequencies of the ν1 fundamental band and the −1−−ν2 − ν2 hot band with uncertainties in the range of 90-600 kHz.
Abstract: We use a Fourier transform spectrometer based on a compact mid-infrared difference frequency generation comb source to perform broadband high-resolution measurements of nitrous oxide, 14N216O, and retrieve line center frequencies of the ν1 fundamental band and the ν1 + ν2 – ν2 hot band. The spectrum spans 90 cm−1 around 1285 cm−1 with a sample point spacing of 3 × 10−4 cm−1 (9 MHz). We report line positions of 72 lines in the ν1 fundamental band between P(37) and R(38), and 112 lines in the ν1 + ν2 – ν2 hot band (split into two components with e/f rotationless parity) between P(34) and R(33), with uncertainties in the range of 90-600 kHz. We derive upper state constants of both bands from a fit of the effective ro-vibrational Hamiltonian to the line center positions. For the fundamental band, we observe excellent agreement in the retrieved line positions and upper state constants with those reported in a recent study by AlSaif et al. using a comb-referenced quantum cascade laser [J Quant Spectrosc Radiat Transf, 2018;211:172-178]. We determine the origin of the hot band with precision one order of magnitude better than previous work based on FTIR measurements by Toth [ http://mark4sun.jpl.nasa.gov/n2o.html ], which is the source of the HITRAN2016 data for these bands.
TL;DR: In this paper, twisted Laguerre-Gaussian Schell model (TLGSM) beams with a prescribed correlation function are introduced, whose twist factor not only exists in the twist phase but also in correlation function.
Abstract: In this paper, we introduce a new class of twisted partially coherent beams with a prescribed correlation function, twisted Laguerre-Gaussian Schell-model (TLGSM) beams, whose twist factor not only exists in the twist phase but also in correlation function Analytical expressions for the cross-spectral density function propagating in free space and in turbulence are derived based on the extended Huygens-Fresnel integral The evolution of the spectral intensity and orbital angular momentum (OAM) are discussed Our results show that adjusting both the mode order and twist factor of the proposed beams to enhance the total OAM of the beams and, simultaneously, improve their resistance to turbulence With multiple degrees of freedom that can be adjusted to optimize the beam for different turbulence conditions, TLGSM beams are an excellent candidate for use in optical applications in challenging media
TL;DR: In this paper, the authors presented measurements of molecular transition frequencies based on the comb-locked cavity ring-down spectroscopy technique, reporting vacuum transition frequencies of Doppler-broadened 12C16O2 in the 1.6 μm region for the (30012) and (33301) states with an average combined standard uncertainty of ≈ 1 kHz.
Abstract: We present measurements of molecular transition frequencies based on the comb-locked cavity ring-down spectroscopy technique, reporting vacuum transition frequencies of Doppler-broadened 12C16O2 in the 1.6 μm region for the (30012) ← (00001) and (30013) ← (00001) bands with an average combined standard uncertainty of ≈ 1 kHz. A global four-state model was fit to these data and literature values to provide spectroscopic parameters and a best-case fit precision of 4 kHz. We identified and quantified an interaction between the (30012) and (33301) states which was manifest as an observed Fermi-resonance-type perturbation in the (30012) ← (00001) band. This interaction was accounted for in the global fit, substantially reducing systematic uncertainties in the spectroscopic parameters of the (30012) state and altering many predicted transition frequencies in the (30012) ← (00001) band by 1 MHz or more relative to literature values. The accurate transition frequencies reported here may be considered as SI-traceable reference data for diverse applications including remote sensing and telecommunications.
TL;DR: In this article, a three-body near-field thermophotovoltaic (NFT) system was designed by introducing an intermediate modulator between thermal emitters and photovolta cells.
Abstract: Near-field thermophotovoltaic devices are attractive energy conversion systems. In the present study, three-body near-field thermophotovoltaic systems are designed by introducing an intermediate modulator between thermal emitters and photovoltaic cells. The slab/grating emitter and modulator are made from Ga-doped ZnO, while the slab/grating cell is made from gallium antimonide. The scattering matrix method is used to calculate the radiative exchange between the emitter and the cell. The performances of three-body systems of slab-slab-slab/slab-slab-grating/ grating-grating-grating are investigated. The numerical results show that the output power of the three-slab system is significantly higher than that of the corresponding two-slab system. The output power improvement is attributed to the introduction of the modulator which enables the plasmon polaritons at two GZO surfaces to be coupled. The one-dimensional grating on the surface of the photovoltaic cell can serve as an anti-reflection pattern and improve the conversion efficiency and output power of the three-body system. Grating emitters and modulators can support hyperbolic modes and enhance the radiative heat flux of the whole system. The results prove that the three-body system can provide the possibility to improve the performance of a near-field thermophotovoltaic device.
TL;DR: In this paper, the results of the analysis of the carbon dioxide absorption band at 3.3 µm in the atmosphere of Mars were used in the analysis and selection rules for both processes are presented.
Abstract: Magnetic dipole and electric quadrupole absorption in carbon dioxide are addressed in details. The selection rules for both processes are presented. The equations for the line intensities are given. In the case of the quadrupole absorption the Herman-Wallis functions are derived. The results of the present paper were used in the analysis of the carbon dioxide absorption band at 3.3 µm in the atmosphere of Mars (Trokhimovskiy A, Perevalov V, Korablev O, Fedorova A, Olsen KS, Bertaux JL, Patrakeev A, Shakun A, Montmessin F, Lefevre F, Lukashevskaya A. First observation of the magnetic dipole CO2 absorption band at 3.3 µm in the atmosphere of Mars by ExoMars Trace Gas Orbiter ACS instrument. A&A 639, A142 (2020)). The retrieved from the Martian atmosphere spectra vibrational transition magnetic dipole moment for the 01111–00001 (ν2+ν3) band of 12C16O2 M 01111 ← 000001 | Δ l 2 | = 1 = 0.96 μ N (where μN is nuclear magneton) is one order of magnitude larger than the gyromagnetic ratio in the case of the rotation-induced magnetic dipole moment.
TL;DR: In this article, the superposition T-matrix scheme was combined with an Ewald sum formulation to account for light scattering in periodic particle arrangements that contain hundreds to thousands of individual scatterers per unit cell.
Abstract: To model and design light propagation in disordered optical nanostructures and materials, any applicable simulation technique has to cope with enormous computational challenges in a bearable time frame. To circumvent these, the introduction of an artificial periodicity to the disordered particle structure allows to rely on computational techniques that exploit periodic boundary conditions. Choosing a rather large periodicity promises to preserve randomness in form of a close-range disorder but can introduce false interferences. So far, it remains open how the artificial periodicity has to be chosen to minimize its detrimental influence. Here, we combine the superposition T-matrix scheme with an Ewald sum formulation to account for light scattering in periodic particle arrangements that contain hundreds to thousands of individual scatterers per unit cell. Simulations reveal that the periodicity’s influence cannot be minimized by simply choosing one single period much longer than the excitation wavelength. The excitation of lattice induced resonances prevents so. However, choosing a periodicity that does not sustain such detrimental features allows for reliable predictions. With that, the presented approach is suitable to derive spectral information about wave-optical phenomena in large, random particle arrangements with a spatial extend beyond those accessible with other full-wave solvers.
TL;DR: In this paper, the authors model UV intensities within spherical approximations of virions randomly positioned within spherical particles and show that shielding of a particle can be reduced by illuminating a particle either from multiple widely separated incident directions, or by illuminating the particle rotating in air for a time sufficient to rotate through enough orientations.
Abstract: UV radiation can inactivate viruses such as SARS-CoV-2. However, designing effective UV germicidal irradiation (UVGI) systems can be difficult because the effects of dried respiratory droplets and other fomites on UV light intensities are poorly understood. Numerical modeling of UV intensities inside virus-containing particles on surfaces can increase understanding of these possible reductions in UV intensity. We model UV intensities within spherical approximations of virions randomly positioned within spherical particles. The model virions and dried particles have sizes and optical properties to approximate SARS-CoV-2 and dried particles formed from respiratory droplets, respectively. In 1-, 5- and 9-µm diameter particles on a surface, illuminated by 260-nm UV light from a direction perpendicular to the surface, 0%, 10% and 18% (respectively) of simulated virions are exposed to intensities less than 1/100th of intensities in individually exposed virions (i.e., they are partially shielded). Even for 302-nm light (simulating sunlight), where absorption is small, 0% and 11% of virions in 1- and 9-µm particles have exposures 1/100th those of individually exposed virions. Shielding is small to negligible in sub-micron particles. Results show that shielding of virions in a particle can be reduced by illuminating a particle either from multiple widely separated incident directions, or by illuminating a particle rotating in air for a time sufficient to rotate through enough orientations. Because highly UV-reflective paints and surfaces can increase the angular ranges of illumination and the intensities within particles, they appear likely to be useful for reducing shielding of virions embedded within particles.