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The existing long-distance transmission line perception mainly focuses on the measurement and analysis of electrical parameters. When the line is subject to wind vibration, icing or galloping, the changes of electrical parameters are not obvious and difficult to capture, resulting in poor performance of long-distance transmission line fault state perception. In this regard, the long-distance transmission line condition sensing based on distributed optical fiber sensing technology is studied. This method designs corresponding sensing methods for four working conditions: using the back Brillouin scattering sensor and phase sensitive Rayleigh scattering sensor in the optical fiber sensing technology to form a multi parameter distributed optical fiber sensing device, which is used to sense the surface temperature, vibration, strain and other data of the long-distance transmission line; By analyzing the linear relationship between fiber Brillouin frequency shift and Brillouin power and fiber strain and temperature, the sensing results of icing thickness of long-distance transmission lines are obtained; By calculating the amplitude and phase information of the detection signal, the sensing results of long-distance transmission line vibration are obtained; By calculating the time difference of polarization mutation signal at both ends of long-distance transmission line, combined with the propagation speed of optical signal and the length of long-distance transmission line, the perception result of lightning fault location of long-distance transmission line can be obtained. The experimental results show that this method can more accurately collect the real-time operation data of long-distance transmission lines, and can effectively perceive the galloping, wind vibration and lightning fault location of long-distance transmission lines. [ABSTRACT FROM AUTHOR]

This article presents a comprehensive study on the impact of irradiation optical fiber cores with a femtosecond-pulsed laser, operating at a wavelength of 1030 nm, on the signal amplitude in Rayleigh scattering-based optical frequency domain reflectometry (OFDR). The experimental study involves two fibers with significantly different levels of germanium doping: the standard single-mode fiber (SMF-28) and the ultra-high numerical aperture fiber (UHNA7). The research findings reveal distinct characteristics of reflected and scattered light amplitudes as a function of pulse energy. Although different amplitude changes are observed for the examined fibers, both can yield an enhancement of amplitude. The paper further investigates the effect of fiber Bragg grating inscription on the overall amplitude of reflected light. The insights gained from this study could be beneficial for controlling the enhancement of light scattering amplitude in fibers with low or high levels of germanium doping. [ABSTRACT FROM AUTHOR]

Rayleigh scattering from a spherical object located near a planar rigid boundary at distances smaller than the wavelength is calculated. Low frequency analysis reduces a scattering problem to a sequence of potential problems. An analytical solution based on expansion in spherical solid harmonics and the use of addition theorem is presented. Analytical perturbation approach is validated by comparison with numerical calculations. The velocity of the center of the particle and the scattering amplitude are determined. In the lowest order in wavenumber, the scattering amplitude is expressed in terms of the monopole and dipole components. In contrast to the behavior of a bubble, under the same conditions, dipole oscillations of the particle in the direction normal to the boundary are not excited and the monopole component of the scattering amplitude does not depend on the location of the particle relative to the boundary. [ABSTRACT FROM AUTHOR]

This paper addresses the challenge posed by the size of certain objects that do not conform to the constraints of microscope‐coupled Raman spectrometers, making sample collection impossible due to their inherent value or nature. Specifically, materials like hydroxyapatite‐based substances used in artistic and ornamental carvings, such as bone or ivory, fall within this problematic category. The focus of this study is the enhancement of analytical capabilities in the context of large objects using a Raman microscope system. The study details the innovation involving a remote probe integrated with fiber optics, elaborating on the design and performance aspects, and emphasizing the appropriateness of chosen components in the analysis of ivory artifacts belonging to private collectors. In order to assess the robustness of our discriminative approaches, an archaeological bone and the exposed dentine in a human tooth were also evaluated and compared. Results showed that using an 805‐nm longpass dichroic mirror successfully directed the near‐infrared laser onto the samples and significantly suppressed the Rayleigh scattering contribution to the spectrum. Regarding the preprocessing methods to spectra evaluation essayed, the most promising approach was the use of principal component analysis for dimension reduction followed by k‐means cluster analysis. By leveraging the complementary strengths of PCA and k‐means clustering, the robustness and interpretability of clustering analyses are enhanced. [ABSTRACT FROM AUTHOR]

This document is an editorial introducing a special issue of the journal Biosensors on the topic of advances in optical biosensors and chemical sensors. The editorial provides an overview of the different types of optical sensors, including fluorescence-based sensors, Raman spectroscopy sensing, and fiber optic-based sensors. It summarizes the main contributions in the special issue, highlighting the working mechanisms and applications of each sensor type. The editorial concludes by discussing the current state of the field and future directions for optical sensor technology. [Extracted from the article]

In order to achieve low-cost scalability, the same-wavelength bidirectional (SWB) fiber communication system is a better solution. We present a detailed investigation of the performance of the different orders Raman amplifiers in same-wavelength bidirectional fiber communication systems. We discuss how to suppress the main factor affecting system performance which is Rayleigh scattering noise (RSN). By using different Raman amplifiers to construct different quasi-lossless transmission, the performance changes in the same-wavelength bidirectional fiber optic communication system were studied. On this basis, multi-channel and same-wavelength single fiber bidirectional system experiments were conducted to compare the performance of second-order Raman systems and first-order Raman systems. The results indicate that the Rayleigh scattering suppression effect of second-order Raman systems is better, and compared to first-order Raman systems, the average signal-to-noise ratio (SNR) can be increased by 2.88 dB. [ABSTRACT FROM AUTHOR]

Abstract Traditionally, Rayleigh scattering is thought to only impact fiber sensing system performance when the leading fiber is over 10 km long. However, this report illustrates theoretically and experimentally that Rayleigh scattering cannot be ignored in fiber optic interferometric sensor (FOIS) even with several hundred‐meter common leading fiber because of the interaction of Rayleigh backward scattering (RBS) and returning interference signal. Herein, a conceptual framework is developed to elucidate the interaction between RBS and FOIS interference, revealing that, beyond laser monochromacity, the self‐correction characteristic of laser pulses also influences coherent superposition. Building upon this novel insight, a phase modulation method based on pseudorandom noise (PRN) code is first proposed to address coherent RBS stacking on returning FOIS interferences while preserving high laser monochromacity. By modulating the interrogation pulses, a 21.3 dB suppression of background phase noise is achieved in FOIS with 3.3 km leading fiber. This study offers a holistic understanding of Rayleigh scattering in the leading fiber, encompassing experimental observations, theoretical modeling, physics analysis, and its resolution, thereby contributing to advancements in underwater sensing to broaden the understanding of the underwater environment.

This paper investigates how atmospheric vertical profiles of pressure, temperature, and concentration affect molecular absorption calculation. This sensitivity analysis is performed in preparation to the upcoming TRUTHS mission, anticipated to provide hyperspectral TOA BRF records with a radiometric accuracy better than 1%. Two methods for characterizing the atmospheric vertical profile are compared: rescaling the H2O and O3 concentrations of an AFGL U.S. Standard vertical profile, and using customized profiles based on CAMS data. The study investigates the effects of those methods on multi-spectral observations in key spectral regions affected, respectively, by water vapour, ozone and methane, as well as on hyperspectral observations covering the visible to SWIR region. Results show that when molecular transmittance exceeds 97%, the choice of method has minimal impact, with less than 1% uncertainty. When the molecular transmittance decreases from 97% to 75%, the corresponding uncertainty on the TOA BRF simulation increases from 1% up to 5%. For transmittance below 75%, using CAMS data for vertical profile characterization is recommended. The study also highlights how pressure and temperature profiles influence Rayleigh optical thickness estimation, particularly affecting TOA BRF in the blue spectral region.

This work reports on the first computational quantum-chemistry implementation of the hyper-Rayleigh scattering optical activity (HRS-OA), a nonlinear chiroptical phenomenon. First, from the basics of the theory, which is based on quantum electrodynamics, and focusing on the electric dipole, magnetic-dipole, and electric-quadrupole interactions, the equations for the simulation of the differential scattering ratios of HRS-OA are re-derived. Then, for the first time, computations of HRS-OA quantities are presented and analyzed. They have been enacted on a prototypical chiral organic molecule (methyloxirane) at the time-dependent density functional theory level using a broad range of atomic orbital basis sets. In particular, (i) we analyze the basis set convergence, demonstrating that converged results require basis sets with both diffuse and polarization functions, (ii) we discuss the relative amplitudes of the five contributions to the differential scattering ratios, and (iii) we study the effects of origin-dependence and derived the expression of the tensor shifts and we prove the origin-independence of the theory for exact wavefunctions. Our computations show the ability of HRS-OA as a nonlinear chiroptical method, able to distinguish between the enantiomers of the same chiral molecule. [ABSTRACT FROM AUTHOR]

AbstractNanosurface-imprinted polymer nanoprobes (Fe3O4@MIP) were prepared by microwave synthesis using Fe3O4 as a nanosubstrate, aspirin as a template, α-methacrylic acid (MAA) as a functional monomer, ethylene glycol dimethacrylate (EGDMA) as a cross-linking agent, and 2,2'-azobisisobutyronitrile (AIBN) as an initiator. Characterization of Fe3O4@MIP revealed that the spectral probe exhibited strong resonance Rayleigh scattering (RRS) for aspirin. With the increase in aspirin concentration, the RRS energy transfer (RRS-ET) was enhanced, and the signal at 370 nm decreased, providing a linear range from 0.25 to 12.5 μmol/L and a detection limit (DL) of 0.08 μmol/L. The developed protocol was used for the determination of aspirin in drugs with recoveries from 93.2 to 102.6. [ABSTRACT FROM AUTHOR]

A highly sensitive distributed measurement technique is employed to map supercontinuum generation along a tapered silica optical fiber. This technique, which utilizes a confocal Raman micro-spectrometer, relies on analyzing far-field frequency-resolved Rayleigh scattering along the waveguide with micrometer-scale spatial resolution and high spectral resolution. Non-destructive and non-invasive, the mapping system enables observation of every stage of supercontinuum generation along the fiber cone, including cascade Raman scattering, four-wave mixing, and dispersive wave generation. Consequently, it unveils unique nonlinear spatial dynamics that are beyond the reach of standard spectral analyzers. [ABSTRACT FROM AUTHOR]

Magnesium aluminate spinel is known to be a material with a good combination of mechanical properties, resistance against chemical attack and a high melting point, being thus a very promising material for application as a transparent material in harsh, high-temperature environments where glass fails. To improve the control over the microstructural evolution during sintering, Eu3+, Y3+ Mg2+ and their combinations were introduced as doping elements. The goal of the study was to optimize processing of fine spinel powder and investigate the potential for enhancing MgAl 2 O 4 spinel density and in-line transmittance by using elements segregating to grain boundaries. The total and in-line transmittance were measured, and the characteristic pore size for transparent samples calculated based on the Rayleigh scattering approximation. Eu-doping proved to be effective in lowering the residual pore size and thus achieving in-line transmittance approaching the theoretical value at relatively low sintering temperatures (1400 °C). [ABSTRACT FROM AUTHOR]

Analyzing three-dimensional excitation-emission matrix (3D-EEM) spectra through machine learning models has drawn increasing attention, whereas the reliability of these machine learning models remains unclear due to their "black box" nature. In this study, the convolutional neural network (CNN) for classifying numbers of fluorescent components in 3D-EEM spectra was interpreted by gradient-weighted class activation mapping (Grad-CAM), guided Grad-CAM, and structured attention graphs (SAGs). Results showed that the original CNN classifier with high classification accuracy may make a classification based on misleading attention to the non-fluorescence area in 3D-EEM spectra. By removing Rayleigh scatterings in 3D-EEM spectra and integrating convolutional block attention module (CBAM) in CNN classifiers, the correct attention of the trained CNN classifier with CBAM greatly increased from 17.6% to 57.2%. This work formulated strategies for improving CNN classifiers associated with environmental fields and would provide great help for water determination in both natural and artificial environments. [ABSTRACT FROM AUTHOR]

Accurate monitoring of small molecules and precise characterization of the secretory ability of neurons are essential for effective diagnosis of neurological diseases. However, existing technologies for monitoring small molecules only provide approximate results. Plasmonic‐based biosensors are a potential solution in this biological application. Nevertheless, optical sensing nanoparticles require precise control of interparticle distance, particle shape and morphology, which can be challenging. This article discovers that the trapping of small molecules to aptamers induces a conformational change that alters the nanostructure of irregularly shaped Au nanoclusters (NCs) and aptamers due to the strong structure‐property relationships of Au NC‐aptamers. This change can be detected via resonance Rayleigh scattering (RRS) intensity in the dark‐field. This new technology overcomes the challenges of precise control of individual nanoparticles and the difficulty of small spectral peak shifts. The Au NC‐aptamers sensing device has a detection limit of 0.112 pm for dopamine, and this work detects 0.226 pm of dopamine surrounding a single epileptic neuron in polarization, which is more than those of healthy neurons. Overall, this easy‐to‐fabricate Au NC‐aptamers‐based technology has a high potential for monitoring small molecules and determining the secretory ability of single neurons, which is not possible using traditional technologies. [ABSTRACT FROM AUTHOR]

Context: In this study, we evaluate the geometrical, absorption, optoelectronic, electronic, nonlinear optical (NLO) and thermodynamic properties of dibenzo[b,def]chrysene molecule derivatives by means of DFT and TD-DFT simulations. In view of the aim of producing new high-performance materials for non-linear optics (NLO) by doping test, two types of doping were used. We obtained six derivatives by doping with organic dopants (Nitro, amide and ticyanoethenyl) and mixed alkali metal (potassium) and organic dopants. Doping with organic dopants produced molecules A, B and C, respectively when substituting one hydrogen with nitro (NO2), amide (CONH2) and tricyanoethenyl (C5N3) groups, while mixed doping involved considering A, B and C and then substituting two hydrogens with two potassiums to obtain compounds D, E and F respectively. The negative values of the various interaction energies calculated for all the doped molecules show that they are all stable, but also that molecules C and F are the most stable in the case of both dopings. The gap energies calculated at the B3LYP level of theory are all below 3 eV, which means that all the molecules obtained are semiconductors. Better still, compounds C and F, with gap energies of 1.852 eV and 1.204 eV, respectively, corresponding to decreases of 35.67% and 58.18% in gap energy compared with the pristine molecule, are more reactive than the other doped molecules. Mixed doping is therefore a highly effective way of narrowing the energy gap and boosting the semiconducting character and reactivity of organic materials. Optoelectronic properties have also been improved, with refractive index values higher than those of the reference material, glass. This shows that our compounds could be used under very high electric field conditions of the order of 4.164 × 109 V.m−1 for C and 7.410 × 109 V.m−1 for F the highest values at the B3LYP level of theory. The maximum first-order hyperpolarizability values for both types of doping are obtained at the CAM-B3LYP level of theory by C: β mol = 92.088 × 10−30esu and by F: β mol = 129.449 × 10−30esu, and second-order values are also given by these same compounds. These values are higher than the reference value, which is urea, making our compounds potential candidates for high-performance NLO applications. In dynamic mode and at a frequency of 1064 nm, at the CAM-B3LYP level of theory, the highest dynamic hyperpolarizability coefficients were obtained by C and F. Hyper-Rayleigh scattering β HRS , coefficients of the electro-optical Pockel effect (EOPE), EFISHG, third-order NLO-response degree four-wave mixing γ DFWM , quadratic nonlinear refractive index n2 were also calculated. The maximum values of n2 are obtained by C (6.13 × 10–20 m2/W) and F (6.60 × 10–20 m2/W), these values are 2.24 times higher than that of fused silica which is the reference for degenerate four-wave mixing so our molecules could also have applications in optoelectronics as wavelength converters, optical pulse modulators and optical switches. Methods: Using the DFT method, we were able to determine the optimized and stable electronic structures of doped dibenzo[b,def]chrysene derivatives in the gas phase. We limited ourselves to using the proven B3LYP and CAMB3LYP levels of theory for calculating electronic properties, and non-linear optics with the 6-311G + + (d,p) basis set, which is a large basis set frequently used for these types of compound. Gaussian 09 software was used to run our calculations, and Gauss View 6.0.16 was used to visualize the output files. TD-DFT was also used to determine absorption properties at the B3LYP level of theory, using the same basis set. [ABSTRACT FROM AUTHOR]

Larger fusion experiments require long beam paths for laser diagnostics, which requires mechanical stability and measures to deal with remaining alignment variations. At the same time, due to technical and organizational boundary conditions, calibrations become challenging. The current mid-sized experiments face the same issues, yet on a smaller scale, which makes them ideal testing environments for novel calibration methods, since a comparison with the established best practices is still possible. At the stellarator Wendelstein 7-X, the calibration and operation of the Thomson scattering diagnostic is hampered by beam displacements, coating of windows during operation, and access restrictions while the superconducting coils are active. New calibration techniques were developed to improve the profile quality and reduce calibration time. While positional variations of the laser beam have to be minimized, the remaining displacements can be accounted for during the absolute calibration. An in situ spectral calibration has been developed based on Rayleigh scattering, which calibrates the whole diagnostic, including observation windows. In addition, a less accurate but faster method has been developed, which utilizes stray-light of a tunable OPO to perform spectral calibration within minutes and does not require torus hall access. Finally, a workflow has been established to consider finite linewidths of the calibration source in the spectral calibration. While these methods will be used at W7-X to complement existing calibration techniques, they may also solve some of the aforementioned issues expected for even larger and nuclear experiments, where access restrictions are stringent and calibration becomes even more demanding. [ABSTRACT FROM AUTHOR]

Based on the Hagena scaling law, the cluster size in a gas jet is dependent on the equivalent diameter of a conical nozzle. In this work, the effect of the equivalent diameter deq of a conical nozzle on cluster size is separated into the individual effects of the throat diameter d and the half-opening angle α by comparing the Rayleigh scattering signals from gas jets. Nine types of conical nozzles with three different throat diameters (0.3, 0.5, and 0.7 mm) and three different half-opening angles (8.5°, 14.0°, and 24.2°) are used to produce argon gas jets at gas backing pressures from 10 up to 80 bar. The experimental results show that the effect of the throat diameter d is almost the same as that expected by the scaling law. However, the scaling law overestimates the effect of the half-opening angle α. The result is helpful for the precise characterization of cluster size and further understanding the interaction between intense laser and gas clusters. [ABSTRACT FROM AUTHOR]

Mass diffusion coefficient measurement techniques with high temporal and spatial resolution have become essential for the research and development of leading-edge technology in a wide range of cross-disciplinary fields, but cannot be achieved using conventional methods. We provide a comprehensive review of the state-of-the-art theoretical and experimental investigations on Soret forced Rayleigh scattering (SFRS), a grating excitation technique (GET) for measuring the mass diffusion coefficient of binary liquid mixtures. SFRS utilizes the Soret effect to create micrometer-order periodic spatial concentration modulation in a sample due to the absorption of an optical interference grating generated by two intersecting heating laser beams. The decay of the concentration modulation by the mass diffusion process within several milliseconds is detected by the diffraction of a probing beam. The theoretical considerations regarding deviations from the ideal mass diffusion conditions are the effects of: (1) the Gaussian beam intensity distribution, (2) the light absorbing material and (3) the cell wall. The proper settings for the optical system are also analyzed, e.g., the effect of coherency and polarization of the heating laser and the effect of the z-direction length of the interference region. We also consider the frame of reference, center of gravity invariance and effect of convection, which are particularly important for mass diffusion experiments. Using the correct implementation of the theory, the optimal SFRS apparatus design and its appropriate use are described in detail. Finally, two successful applications of SFRS are demonstrated using visible light laser heating and mid-wavelength infrared gas laser heating. [ABSTRACT FROM AUTHOR]

In this work, we present a metastable helium lidar system for the measurements of metastable helium He(23S) density in the thermosphere and lower exosphere. This lidar system consists of a high power 1,083 nm pulsed laser, a 1 m aperture laser beam expander, six 1 m aperture receiving telescopes and a superconducting nanowire single‐photon detector (SNSPD). This system realizes metastable helium density detection up to 1,000 km. Daily rapid variation of metastable helium density within several hours was measured with a height resolution of 50 km for the first time. It demonstrates the capability of ground‐based lidar for continuous height‐resolved detection of the atmospheric metastable helium in the height range of 200–1,000 km. This is a promising tool to help study the coupling of neutral and ionized atmosphere in this height range and further providing observation basis for space weather prediction. Plain Language Summary: Many different kinds of lidar have been well developed for tens of years and can detect the atmosphere up to 180 km by different principles (such as aerosol scattering, Rayleigh scattering, resonance fluorescence scattering and so on). However, in the higher height range of 200–1,000 km, there are almost no suitable methods to monitoring the atmosphere continuously from the ground, except for one choice: metastable helium lidar. In this work, we built a powerful 1,083 nm pulsed laser and emit it vertically in to the atmosphere, the metastable helium atoms resonance with the laser and emits fluorescence photons. The scattered photons from the very high atmosphere are collected and focused by the large aperture telescope on the ground and detected by the photoelectric detector. Building such a lidar has many difficulties that have never been encountered by other conventional lidars, such as the large signal attenuation by long distance. This powerful lidar is built successfully in 2023 and make observations for several months. The first high quality initial data of the observed metastable helium density profile in 200–1,000 km is shown in this paper. This observation will continuously provide useful observation for the study of space physics and space weather forecasting. Key Points: A metastable helium lidar system for the measurements of metastable helium He(23S) density in 200–1,000 km has been developedDaily rapid variation of metastable helium density within several hours was measured with a height resolution of 50 km for the first timeThis is a promising tool to help providing observation basis for space weather prediction [ABSTRACT FROM AUTHOR]

Raman scattering is sensitive to local temperature and thus offers a convenient tool for non-contact and non-destructive optical thermometry at the nanoscale. In turn, all-dielectric nanostructures, such as silicon particles, exhibit strongly enhanced photothermal heating due to Mie resonances, which leads to the strong modulation of elastic Rayleigh scattering intensity through subsequent thermo-optical effects. However, the influence of the complex photo-thermo-optical effect on inelastic Raman scattering has yet to be explored for resonant dielectric nanostructures. In this work, we experimentally demonstrate that the strong photo-thermo-optical interaction results in the nonlinear dependence of the Raman scattering signal intensity from a crystalline silicon nanoparticle via the thermal reconfiguration of the resonant response. Our results reveal a crucial role of the Mie resonance spectral sensitivity to temperature, which modifies not only the conversion of the incident light into heat but also Raman scattering efficiency. The developed comprehensive model provides the mechanism for thermal modulation of Raman scattering, shedding light on the photon–phonon interaction physics of resonant material, which is essential for the validation of Raman nanothermometry in resonant silicon structures under a strong laser field. [ABSTRACT FROM AUTHOR]

Measuring the size of suspended particles in water is crucial in related fields such as environmental engineering, marine engineering, and hydraulic engineering. Considering the size distribution of suspended particles in real rivers, the amplitude (Amp) of the backscattering of particles with sizes ranging from 0.006 mm to 0.030 mm was analysed in this research using a lightweight ultrasonic meter developed by the authors and four probes with bandwidths ranging from 3.0 MHz to 30.0 MHz. In the analysis of Amp measurements for different particle sizes, using 0.008 mm as the reference particle size and converting to the rest of the particle sizes, if the Rayleigh scattering condition is satisfied between the particle sizes and the probe frequency, the conversion error value will be between −10% and 10%. This verifies the correctness of the theoretically derived particle size-Amp theory (the positive power relationship between the particle sizes and the Amp) and reflects the validity constraints of designing this experimental setup. The measurement method based on particle backscattering Amp analysis utilised in this study will help to achieve real-time measurements of suspended particles at river sites. [ABSTRACT FROM AUTHOR]

There exist issues of ill-adaptability and low-accuracy in ultrasonic bolt stress measurement based on acoustic elasticity and scattering attenuation. Therefore, a bolt axial stress measurement method based on ultrasound multi-feature fusion is proposed in this paper. Firstly, ultrasound characteristic parameters based on the theory of acoustic elasticity are extracted, including the difference of time-of-flight (TOF) and the longitudinal wave attenuation coefficient in polycrystalline materials within the Rayleigh scattering range. Then, following the dimension reduction principle, the difference of TOF, attenuation coefficient, and clamping length are chosen as the input feature vectors for the fusion model. Subsequently, the SVR model is employed to establish a multi-feature fusion model for bolt axial stress measurement. Calibration and measurement experiments are conducted using the constructed experimental platform. Comparative analysis between the traditional measurement methods and the proposed method reveals that the SVR model can adapt to measurements of bolts with different lengths, overcoming the limitations of traditional methods. Furthermore, the measurement results of different fusion algorithms show that SVR yields significantly lower average relative errors in the measurement of the three bolts (3.35%, 4.44%, and 4.48%) compared to BP and RBF algorithms. This indicates higher measurement accuracy and immunity to low-stress effects. [ABSTRACT FROM AUTHOR]

A multi-sensor information fusion algorithm based on fault-tolerant Kalman filter is proposed in phase-sensitive optical time-domain reflectometer (Φ-OTDR) system, for achieving fading-free distributed vibration sensing. Firstly, a fault-tolerant dual-core complementary array model is designed. The Rayleigh scattering signal denoising, and vibration existence judgment of localization points are carried out to obtain the differentiated frequency demodulation results of the sensing points of the dual-core fiber array. Then a fault-tolerant control strategy is used to determine the sensor weight coefficients and vibration judgment coefficients during data fusion processing, and array data fusion is carried out based on time series data using Kalman filter to realize error value identification and filling. The advantage of this method is the combination of redundant data in a complementary way to improve the system stability. The frequency response ranges from 10 Hz to 2400 Hz and the localization accuracy is 98.33%. The influence of key parameters on the frequency demodulation performance of fault-tolerant Kalman filter is discussed, and a standard deviation of 14.6 Hz and an average error of 7.6 Hz are obtained. The demodulation frequency data matrix obtained by the classical demodulation method has a demodulation error probability of 89.18%, which proves the widespread existence of demodulation errors in vibration signals. The fusion error of demodulation frequency is reduced to 0.25 Hz, the frequency demodulation accuracy reaches 100%, and the demodulation error caused by interference attenuation can be completely eliminated. This system based on fault-tolerant Kalman filter has the characteristics of simple multiplexing structure, interference fading resistance and stable demodulation performance. • A sensor information fusion algorithm based on fault-tolerant Kalman filter is proposed to achieve fading-free sensing. [ABSTRACT FROM AUTHOR]

New and effective D–π–A and D–π–A–π–A systems of chromophores 1–4 based on the ferrocene core have been synthesized using Knoevenagel condensation reactions and the characterization of chromophores 1–4 was done by modern spectroscopic methods. Moreover, 2 and 4 structures were confirmed using the single crystal X-ray diffraction (SC-XRD) technique. Crystal packing revealed that the chromophores are centrosymmetric and show non-covalent interactions. The observed positive solvatochromism reveals that the stabilization of molecules is greater in excited states than in the ground states. The fluorescence spectra of all the chromophores display weak emission in the solution state, and enhanced emission was observed in a THF:H2O mixture, due to the restriction of intramolecular rotation (RIR), and it is known as aggregation-induced emission (AIE). The SHG (second harmonic generation) measurements were done by the Kurtz–Perry powder method with potassium dihydrogen phosphate (KDP) as a reference material. The presence of hydrogen bonding interactions in the molecules blocks the anti-parallel arrangements and shows second order NLO properties in the bulk, in spite of the fact that chromophores 2 and 4 crystallize in the centrosymmetric space group. The first hyperpolarizabilities (β) [β = 56.5 × 10−30 esu (2); β = 81.5 × 10−30 esu (4)] were measured using the hyper Rayleigh scattering (HRS) technique. Chromophore 4 shows enhanced second-order NLO response compared to the other chromophores, due to an extra phenyl group in the molecule creating more planarity and enhancing the conduction of charges, which happens within a molecule (ICT process), between the ferrocene and acceptor groups (–CN and –NO2). The experimental results were corroborated using DFT calculations that comprise functionals like LC-BLYP, CAM-B3LYP and B3LYP and the 6-31+G** level of theory. [ABSTRACT FROM AUTHOR]

A technique is developed for determining the sound field scattered by a compact body when it is close enough to an acoustic source to be in its near field. Our approach is based on the fact that large regions of many near fields may be well approximated at each point in space by a subsonic plane wave (also called an inhomogeneous plane wave, or an evanescent wave). Such a wave is defined by the property that in one direction it propagates with subsonic phase speed, while in a perpendicular direction it has exponential amplitude variation. Hence by defining a canonical problem, compact scattering of a subsonic plane wave, and solving it, we are able to give a unified analytical treatment of many near-field scattering problems. Our approach draws on the formulae of Rayleigh scattering (as applied to an incident field with complex wavenumber) and the asymptotic theory of the wave equation. For an arbitrary three-dimensional multipole, we determine in full detail how its subsonic wave structure depends on the spherical harmonic parameters (m,n) , and show that our approach has a very large region of validity. [ABSTRACT FROM AUTHOR]

This study investigates the combustion characteristics of nonpremixed bluff-body stabilized H 2 /N 2 -air flames, with a specific focus on a fully cracked ammonia case. The motivation behind this exploration lies in the potential of such flames to contribute to low-carbon combustion technologies, serving as both a reference and a first step towards understanding the role of the recirculation zone on the in-situ cracking of ammonia bluff-body stabilized flames. Simultaneous Raman/Rayleigh measurements of temperature and major species are utilized to validate the numerical model, offering a detailed characterization of the flame structure. To achieve computational efficiency at high fidelity, the simulation algorithm employs a data-driven approach that combines principal component analysis (PCA) with deep neural networks (DNNs). The model incorporates differential diffusion and subgrid-scale effects. The proposed PC-DNN approach includes differential diffusion based on a rotation technique, utilizing the mixture-averaged (MA) transport model for the training dataset. To show the potential of the PC-DNN approach in modeling fully cracked ammonia flames, the study compares large eddy simulation (LES) results with recent Raman/Rayleigh scattering measurements obtained at KAUST. The findings reveal that the PC-DNN method accurately captures key flame features with just two principal components. Incorporating differential diffusion and subgrid-scale effects enhances predictions, despite some inconsistencies in fuel-rich areas, and in the far field of the burner exit where mixing is predominant, suggesting further room for improvement in the model. This research sheds light on the complex dynamics of fully cracked ammonia flames, providing valuable insights for advancing low-carbon combustion technologies. • H 2 /N 2 -air bluff-body stabilized flames are studied. • Differential diffusion in PCA-based models with subgrid closure is considered. • Accounting for differential diffusion and subgrid-scale effects enhances predictions. • Flame structure in fully cracked ammonia is revealed, showing double layers of OH. [ABSTRACT FROM AUTHOR]

Acoustic vibrations of matter convey fundamental viscoelastic information that can be optically retrieved by hyperfine spectral analysis of the inelastic Brillouin scattered light. Increasing evidence of the central role of the viscoelastic properties in biological processes has stimulated the rise of non-contact Brillouin microscopy, yet this method faces challenges in turbid samples due to overwhelming elastic background light. Here, we introduce a common-path Birefringence-Induced Phase Delay (BIPD) filter to disentangle the polarization states of the Brillouin and Rayleigh signals, enabling the rejection of the background light using a polarizer. We demonstrate a 65 dB extinction ratio in a single optical pass collecting Brillouin spectra in extremely scattering environments and across highly reflective interfaces. We further employ the BIPD filter to image bone tissues from a mouse model of osteopetrosis, highlighting altered biomechanical properties compared to the healthy control. Results herald new opportunities in mechanobiology where turbid biological samples remain poorly characterized. Non-contact Brillouin microscopy holds potential to disrupt mechanobiology, yet this method faces challenges in presence of strong Rayleigh scattering. Here, the authors introduce a common-path birefringent filter exhibiting ultra-high extinction ratio to investigate turbid biological samples. [ABSTRACT FROM AUTHOR]

This article presents a LiDAR system that utilizes a Fizeau interferometer and photomultiplier tube array to detect the water Rayleigh–Brillouin spectrum, utilized to obtain underwater temperature and salinity synchronizing measurements based on the Brillouin spectral linewidth and shift. Temperature and salinity measurements were conducted in the laboratory to verify the efficiency of the system. The results demonstrate that the LiDAR system can accurately obtain the Rayleigh–Brillouin spectral backscattering profiles of water. Following linear fitting and reconstruction, the retrieved temperature accuracy is ±0.13 °C and salinity accuracy is ±0.16‰. By effectively leveraging the multiparameter information contained in the Rayleigh–Brillouin spectrum, the system achieved precise temperature and salinity measurements. This study provides a reference for marine remote sensing applications [ABSTRACT FROM AUTHOR]

In this work, a nanogold surface molecularly imprinted polymer spectral probe (AuNP@MIP) for selectively identifying ferrocyanide was prepared under microwave irradiation using nanogold as the core, ferrocyanide as the template ion, methacrylic acid as the monomer, and ethylene glycol dimethacrylate as the cross-linking agent. AuNP@MIP was found to produce a resonance Rayleigh scattering (RRS) peak at 370 nm. When potassium ferrocyanide (K4Fe(CN)6) was present, a AuNP@MIP-Fe(CN)6 complex was formed, producing RRSenergy transfer (RRS-ET). With an increase in ferrocyanide concentration within a certain range, the RRS intensity at 370 nm decreased linearly, and the detection range was 0.02-0.40 µmol L-1, with a detection limit as low as 0.006 µmol L-1 ferrocyanide. This new method has the advantages of simplicity, rapidity, and selectivity when applied for the determination of K4Fe(CN)6 in table salt. [ABSTRACT FROM AUTHOR]

Gas flow visualization is an essential technique for understanding the gas flow characteristics. Various quantitative distribution measurement methods have been proposed, each with its own advantages and disadvantages. For example, the background-oriented schlieren method provides the quantitative density distribution for wide areas with a simple optical setup, but it disadvantageously requires the appropriate boundary conditions need to be set when integrating the Poisson equation. The laser Rayleigh scattering method also provides quantitative density distribution, but it requires a high-power laser for wide-area measurements because laser intensity directly influences measurement accuracy. This study proposes a method that complements the weak points of the above two methods. First, a wide area is measured using the background-oriented schlieren method, and then, the laser Rayleigh scattering method is applied only for the boundary region to obtain the boundary condition. For a heated turbulent air jet with Reynolds number 3000, the results of the proposed method are compared with the numerical analysis and thermocouple temperature measurements. The results well match, indicating the applicability and usefulness of the proposed method. Furthermore, these results contribute to demonstrating the significance of boundary conditions in the background-oriented schlieren method and the establishment of setting guidelines. [ABSTRACT FROM AUTHOR]

Some well-known mathematical techniques have been used to compute the reliability of a parallel-series system of order (2,3,1). The system is composed of four units labelled as A, B, C and D. The configuration involves two parallel subsystems: the first containing units A, B and C arranged in series and the second comprising a single unit D. The failure rate of units is assumed to follow the Rayleigh distribution. With the use of the decomposition method, cut set method and event space method, expressions for both reliability and Mean Time to System Failure (MTSF) have been derived. By considering all units to be identical, the reliability measures have been obtained numerically for specific parameter values. The trends of these measures have been represented graphically to understand the effect of parameters. The study has its practical significance in assessing the reliability of solar panel system. [ABSTRACT FROM AUTHOR]

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Jian kiln oil-spot glaze is one of the most typical iron crystal precipitation glazes in ancient China, and it is important to clarify the influence of iron oxide on precipitation glazes coloration and crystal precipitation, to provide a scientific basis and theoretical guidance for the development and innovation of iron crystal precipitation glazes with a variety of coloration effects. In this paper, XRD, Raman, SEM and EDS testing methods were used to investigate the microstructure of the precipitated crystals in glaze melt and the change rules of glaze coloration with different iron oxide content, and to reveal the mechanism of the glaze crystal structure on coloration. The results show that with the increase of iron oxide content, the glaze surface precipitates brownish-yellow, silver-blue, silver-white, silver-white and reddish-brown crystal spots, and the crystal spots are colored by chemical color and structural color coupling effect of crystals. The iron enrichment in the middle area of crystal spot is higher than that in edge area, and the phase change from ε-Fe2O3 to α-Fe2O3 takes place preferentially, forming different color effects. The middle area first precipitates 2 ~ 4 µm leaf-shaped ε-Fe2O3 crystals, with brownish yellow. With the increase of iron oxide content, the glaze layer precipitates with the glaze surface parallel to the directional arrangement of rod-shaped α-Fe2O3 crystals to form crystalline thin film, which produces a strong reflection of light, being silver-white. When the iron oxide continues to increase, the glaze precipitation of 10 ~ 20 µm dendritic α-Fe2O3 crystals penetrates the crystalline thin film, the structural color (silver) produced by the film is weakened, and the chemical color of α-Fe2O3 (reddish brown) is enhanced. The coupling is silver-white with reddish brown. The edge area first precipitates a large number of 30 ~ 50 nm grains, resulting in Rayleigh scattering as blue. With the increase of iron oxide content, the surface layer of rod-like crystals also forms a crystal film and the lower layer of film precipitates 100 ~ 200 nm plate nanocrystals to form amorphous photonic crystals. The coherent scattering is blue, and the reflected silver-white is coupled with silver blue. [ABSTRACT FROM AUTHOR]

In this work, evolution of parameters of nanosecond repetitively pulsed (NRP) discharges in pin-to-pin configuration in air was studied during the transient stage of initial 20 discharge pulses. Gas and plasma parameters in the discharge gap were measured using coherent microwave scattering, optical emission spectroscopy, and laser Rayleigh scattering for NRP discharges at repetition frequencies of 1, 10, and 100 kHz. Memory effects (when perturbations induced by the previous discharge pulse would not decay fully until the subsequent pulse) were detected for the repetition frequencies of 10 and 100 kHz. For 10 kHz NRP discharge, the discharge parameters experienced significant change after the first pulse and continued to substantially fluctuate between subsequent pulses due to rapid evolution of gas density and temperature during the 100 μs inter-pulse time caused by intense redistribution of the flow field in the gap on that time scale. For 100 kHz NRP discharge, the discharge pulse parameters reached a new steady-state at about five pulses after initiation. This new steady-state was associated with well-reproducible parameters between the discharge pulses and substantial reduction in breakdown voltage, discharge pulse energy, and electron number density in comparison to the first discharge pulse. For repetition frequencies 1–100 kHz considered in this work, the memory effects can be likely attributed to the reduction in gas number density and increase in the gas temperature that cannot fully recover to ambient conditions before subsequent discharge pulses. [ABSTRACT FROM AUTHOR]

Particulate physical gels are sparse, low-density amorphous materials in which clusters of glasses are connected to form a heterogeneous network structure. This structure is characterized by two length scales, ξs and ξG: ξs measures the length of heterogeneities in the network structure and ξG is the size of glassy clusters. Accordingly, the vibrational states (eigenmodes) of such a material also exhibit a multiscale nature with two characteristic frequencies, ω * and ωG, which are associated with ξs and ξG, respectively: (i) phonon-like vibrations in the homogeneous medium at ω < ω * , (ii) phonon-like vibrations in the heterogeneous medium at ω * < ω < ω G , and (iii) disordered vibrations in the glassy clusters at ω > ωG. Here, we demonstrate that the multiscale characteristics seen in the static structures and vibrational states also extend to the phonon transport properties. Phonon transport exhibits two distinct crossovers at frequencies ω* and ωG (or at wavenumbers of ∼ ξ s − 1 and ∼ ξ G − 1 ). In particular, both transverse and longitudinal phonons cross over between Rayleigh scattering at ω < ω * and diffusive damping at ω > ω * . Remarkably, the Ioffe–Regel limit is located at the very low frequency of ω*. Thus, phonon transport is localized above ω*, even where phonon-like vibrational states persist. This markedly strong scattering behavior is caused by the sparse, porous structure of the gel. [ABSTRACT FROM AUTHOR]

Laser shadowgrams of exploding metal wires in a vacuum show the anomalous transparency of a completely evaporated wire core for a probe beam with a wavelength of 1064 nm. Simultaneous shadowgrams at 532 nm show significant light attenuation. The anomalous transparency for laser radiation at a wavelength of 1064 nm is highly likely due to the Rayleigh scattering of the probing beam by metal atoms. Our experimental results can be explained under the assumption of a strongly non-equilibrium state of an expanding gas cylinder with a non-uniform density. [ABSTRACT FROM AUTHOR]

The electrocatalytic CO2 reduction reaction (eCO2RR) stands out as a highly promising approach to simultaneously resolving the issue of the elevated atmospheric CO2 concentration and its utilization to produce value-added products. One of the present challenges is the rational design of efficient catalysts toward the eCO2RR and the understanding of their structure–activity relationship. Covalent porous catalysts (CPCs) with atomically dispersed active sites embedded in the porous organic backbone, including polymer-based catalysts, such as covalent organic frameworks (COFs) and conjugated microporous polymers (CMPs), and molecule-based catalysts, such as porous organic cages (POCs) have received increasing attention recently. They feature extremely high atom utilization, customizable porosity, a customizable backbone, and distinct electronic properties. In this review, the design principles of CPCs, both in their selection of metal sites (metallic centers, heterometallic centers and their axial coordination) and optimization of organic backbones (chelating sites, their electronic modulation and microstructures) will be covered, aiming to provide guidance to tune their eCO2RR performance. Then representative examples will be discussed to reveal their structure–activity relationships. The perspective and key challenges in CPC based eCO2RR electrocatalysts will be finally proposed. [ABSTRACT FROM AUTHOR]

The electrocatalytic CO2 reduction reaction (eCO2RR) stands out as a highly promising approach to simultaneously resolving the issue of the elevated atmospheric CO2 concentration and its utilization to produce value-added products. One of the present challenges is the rational design of efficient catalysts toward the eCO2RR and the understanding of their structure–activity relationship. Covalent porous catalysts (CPCs) with atomically dispersed active sites embedded in the porous organic backbone, including polymer-based catalysts, such as covalent organic frameworks (COFs) and conjugated microporous polymers (CMPs), and molecule-based catalysts, such as porous organic cages (POCs) have received increasing attention recently. They feature extremely high atom utilization, customizable porosity, a customizable backbone, and distinct electronic properties. In this review, the design principles of CPCs, both in their selection of metal sites (metallic centers, heterometallic centers and their axial coordination) and optimization of organic backbones (chelating sites, their electronic modulation and microstructures) will be covered, aiming to provide guidance to tune their eCO2RR performance. Then representative examples will be discussed to reveal their structure–activity relationships. The perspective and key challenges in CPC based eCO2RR electrocatalysts will be finally proposed. [ABSTRACT FROM AUTHOR]

In this paper, we present the new multi-wavelength dataset of aerosol extinction profiles, which are retrieved from the averaged transmittance spectra by the Global Ozone Monitoring by Occultation of Stars instrument aboard the Envisat satellite. Using monthly and zonally averaged transmittances as a starting point for the retrievals enables us to improve the signal-to-noise ratio and eliminate possible modulation of transmittance spectra by uncorrected scintillations. The two-step retrieval method is used: the spectral inversion is followed by the vertical inversion. The spectral inversion relies on the removal of contributions from ozone, NO2 , NO3 and Rayleigh scattering from the optical depth spectra for each ray perigee altitude. In the vertical inversion, the profiles of aerosol extinction coefficients at several wavelengths are retrieved from the collection of slant aerosol optical depth profiles. The retrieved aerosol extinction profiles (FMI-GOMOSaero dataset v1) are provided in the altitude range 10–40 km at wavelengths of 400, 440, 452, 470, 500, 525, 550, 672 and 750 nm for the whole GOMOS operating period from August 2002 to March 2012. Extensive intercomparisons of the retrieved FMI-GOMOSaero aerosol profiles with aerosol profile data from other satellite instruments at several wavelengths have been performed. It is found that the average difference between FMI-GOMOSaero and other datasets is within 20 %–40 % in the lower and middle stratosphere, the standard deviation is ∼ 20 %–50 %, and the correlation coefficient of the time series is 0.65–0.85. The created FMI-GOMOSaero dataset can be used in merged datasets of stratospheric aerosols. It might be also used as a priori information for satellite retrievals during 2002–2012. [ABSTRACT FROM AUTHOR]

Perylenetetracarboxylic diimide (PTCDI) is an n-type organic semiconductor molecule that has been widely utilized in numerous applications such as photocatalysis and field-effect transistors. Polarizability and dipole moment, which are inherent properties of molecules, are important parameters that determine their responses to external electric and optical fields, physical properties, and reactivity. These parameters are fundamentally important for the design of innovative materials. In this study, the effects of external electric fields on absorption and fluorescence spectra were investigated to obtain the PTCDI parameters. The PTCDI substituted by an octyl group (N,N′-Dioctyl-3,4,9,10-perylenedicarboximide) dispersed in a polymethyl methacrylate (PMMA) matrix was studied in this work. The features of vibronic progression in the absorption spectrum were analogous to those observed in solution. The red shift of the absorption band caused by the Stark effect was mainly observed in the presence of an external electric field. Changes in parameters such as the dipole moment and polarizability between the ground and the Franck–Condon excited states of the PTCDI monomer were determined. The fluorescence spectrum shows a contribution from a broad fluorescence band at wavelengths longer than the monomer fluorescence band. This broad fluorescence is ascribed to the excimer-like fluorescence of PTCDI. The effects of the electric field on the fluorescence spectrum, known as the Stark fluorescence or electrofluorescence spectrum, were measured. Fluorescence quenching is observed in the presence of an external electric field. The change in the polarizability of the monomer fluorescence band is in good agreement with that of the electroabsorption spectrum. A larger change in the polarizability was observed for the excimer-like fluorescence band than that for the monomer band. This result is consistent with exciton delocalization between PTCDI molecules in the excimer-like state. [ABSTRACT FROM AUTHOR]

Optical phase curves of hot Jupiters can reveal global scattering properties. We implemented a Bayesian inference framework for optical phase curves with flux contributions from: reflected light from a potentially inhomogeneous atmosphere, thermal emission, ellipsoidal variations, Doppler beaming, and stellar rotation via a Gaussian process in the time domain. We probed for atmospheric homogeneity and time variability using the reflected light inferences for highly precise Kepler light curves of five hot Jupiters. We also investigated the scattering properties that constrain the most likely condensates in the inhomogeneous atmospheres. Cross validation prefers inhomogeneous albedo distributions for Kepler-7 b and Kepler-41 b, and a weak preference for inhomogeneity for KOI-13 b. None of the five planets exhibit significant variations in geometric albedo on 1-yr timescales, in agreement with theoretical expectations. We show that analytic reflected light phase curves with isotropic multiple scattering are in excellent agreement with full Rayleigh multiple scattering calculations, allowing for accelerated and analytic inference. In a case study of Kepler-41 b, we identified perovskite, forsterite, and enstatite as possible scattering species consistent with the reflected light phase curves, with condensate particle radii in the range 0.01–0.1 µm. [ABSTRACT FROM AUTHOR]

The propagation characteristics of elastic waves in polycrystalline materials depend not only on grain size, but also on grain size distribution. In this paper, based on Weaver's polycrystalline scattering model, two grain size distribution models, namely the truncated lognormal distribution and the fractal distribution based on fractal dimension, are considered. At the same time, the ultrasonic attenuation of polycrystalline materials is studied by considering the existence of finite interval of grain size. The grain size of the classical lognormal distribution ranges from zero to infinity, which is inconsistent with the actual situation. The present work modifies Turner's study based on the lognormal distribution and compares the numerical results with Turner's. The numerical results obtained from the two kinds of distributions show that the scattering attenuation in the Rayleigh scattering region is affected by both the grain size distribution and the average grain size. In the transition scattering region, the attenuation of P-wave scattering is related to the average grain size and size distribution, while the attenuation of S-wave scattering is mainly affected by the average grain size. In the stochastic scattering region, the scattering attenuation is mainly affected by the average grain size and is not sensitive to the grain size distribution. Moreover, the numerical results also show that the difference of scattering attenuation due to the grain size distribution is most obvious in the Rayleigh scattering region. [ABSTRACT FROM AUTHOR]

The full‐screen mobile phone can be fabricated by integrating the camera beneath the screen, which needs the nanocomposite light guide plate (nano‐LGP) with exceptional transparency and light‐guiding properties simultaneously. Choosing an appropriate nanoparticle with a high refractive index and exceptional compatibility within the polymer matrix is crucial for producing the nano‐LGP. In this study, the high refractive index carbonized polymer dots (HRI‐CPDs) are synthesized through the solvothermal treatment, achieving a refractive index value of 1.7220 at 450 nm. Subsequently, the modified HRI‐CPDs (mHRI‐CPDs)/polymethyl methacrylate (PMMA) nanocomposites are fabricated by copolymerizing the mHRI‐CPDs with methyl methacrylate. Due to the high visible light transmittance and Rayleigh scattering characteristics when light passes through the nanocomposites, this kind of nanocomposites is suitable for serving as nano‐LGPs. The potential of carbonized polymer dots as light‐scattering unit is originally explored to improve surface illuminance and uniformity of nano‐LGPs. The best‐performing 4.3‐inch LGP with 1.0 wt.% doping content shows 15.8 times higher surface illuminance and 2.1 times higher uniformity than pure PMMA. This new type of LGP based on mHRI‐CPDs/PMMA nanocomposite holds tremendous promise in conjunction with advanced liquid crystal display technology. [ABSTRACT FROM AUTHOR]