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Determining the correlation between the size of a single quantum dot (QD) and its photoluminescence (PL) properties is a challenging task. In the study, we determine the size of each QD by measuring its absorption cross section, which allows for accurate investigation of size-dependent PL blinking mechanisms and volume scaling of the biexciton Auger recombination at the single-particle level. A significant correlation between the blinking mechanism and QD size is observed under low excitation conditions. When the QD size is smaller than their Bohr diameter, single CsPbI3 perovskite QDs tend to exhibit BC-blinking, whereas they tend to exhibit Auger-blinking when the QD size exceeds their Bohr diameter. In addition, by extracting bright-state photons from the PL intensity trajectories, the effects of QD charging and surface defects on the biexcitons are effectively reduced. This allows for a more accurate measurement of the volume scaling of biexciton Auger recombination in weakly confined CsPbI3 perovskite QDs at the single-dot level, revealing a superlinear volume scaling (τXX,Auger ∝ σ1.96). [ABSTRACT FROM AUTHOR]

Entangled two-photon absorption (ETPA) could form the basis of nonlinear quantum spectroscopy at very low photon fluxes, since, at sufficiently low photon fluxes, ETPA scales linearly with the photon flux. When different pairs start to overlap temporally, accidental coincidences are thought to give rise to a "classical" quadratic scaling that dominates the signal at large photon fluxes and, thus, recovers a supposedly classical regime, where any quantum advantage is thought to be lost. Here, we scrutinize this assumption and demonstrate that quantum-enhanced absorption cross sections can persist even for very large photon numbers. To this end, we use a minimal model for quantum light, which can interpolate continuously between the entangled pair and a high-photon-flux limit, to analytically derive ETPA cross sections and the intensity crossover regime. We investigate the interplay between spectral and spatial degrees of freedom and how linewidth broadening of the sample impacts the experimentally achievable enhancement. [ABSTRACT FROM AUTHOR]

Resonant intermediate states have been proposed to increase the efficiency of entangled two-photon absorption (ETPA). Although resonance-enhanced ETPA (r-ETPA) has been demonstrated in atomic systems using bright squeezed vacuum, it has not been studied in organic molecules. We investigate for the first time r-ETPA in an organic molecular dye, indocyanine green (ICG), when excited by broadband entangled photons in near-IR. Similar to many reported virtual state mediated ETPA (v-ETPA) measurements, no r-ETPA signals are measured, with an experimental upper bound for the cross section placed at 6(±2) × 10−23 cm2. In addition, the classical resonance-enhanced two-photon absorption (r-TPA) cross section of ICG at 800 nm is measured for the first time to be 20(±13) GM, where 1 GM equals 10−50 cm4 s, suggesting that having a resonant intermediate state does not significantly enhance two-photon processes in ICG. The spectrotemporally resolved emission signatures of ICG excited by entangled photons are also presented to support this conclusion. [ABSTRACT FROM AUTHOR]

We conducted a study on the variations of the fragment anisotropy parameters (β) along the Fano profiles for the predissociation of the D2 molecule. These variations, known as β profiles, were measured for the D(2l) fragments from the predissociation of the 4 p π D ′ Π u 1 υ ′ = 1 and 4 p σ B ″ Σ u + 1 υ ′ = 2 states. The measured β profiles show significant asymmetry and broader linewidths compared to the corresponding Fano profiles. By fitting the β profiles, we were able to determine the fragment anisotropy parameters associated with the resonance state, continuum state, and the interference effect between them. Additionally, we determined the ratios of the absorption cross sections between the unperturbed and perturbed continuum states interacting with the resonance states although these ratios were found to be very small. Furthermore, we derived approximate formulas to calculate the parameters characterizing the β profile. Despite the linewidths of the four Fano profiles being narrower than our instrumental resolution, we were still able to determine the product of the linewidth with the Fano q parameters. These findings demonstrate the utility of the β profile as an effective tool for studying the predissociation dynamics in diatomic molecules. [ABSTRACT FROM AUTHOR]

We present a detailed theoretical analysis of polarized absorption spectra and linear dichroism of cyanine dye aggregates whose unit cells contain two molecules. The studied threadlike ordered system with a molecular exciton delocalized along its axis can be treated as two chains of conventional molecular aggregates, rotated relative to each other at a certain angle around the aggregate axis. Our approach is based on the general formulas for the effective cross section of light absorption by a molecular aggregate and key points of the molecular exciton theory. We have developed a self-consistent theory for describing the orientational effects in the absorption and dichroic spectra of such supramolecular structures with nonplanar unit cell. It is shown that the spectral behavior of such systems exhibits considerable distinctions from that of conventional cyanine dye aggregates. They consist in the strong dependence of the relative intensities of the J- and H-type spectral bands of the aggregate with a nonplanar unit cell on the angles determining the mutual orientations of the transition dipole moments of constituting molecules and the aggregate axis as well as on the polarization direction of incident light. The derived formulas are reduced to the well-known analytical expressions in the particular case of aggregates with one molecule in the unit cell. The calculations performed within the framework of our excitonic theory combined with available vibronic theory allow us to quite reasonably explain the experimental data for the pseudoisocyanine bromide dye aggregate. [ABSTRACT FROM AUTHOR]

A two-component contour deformation (CD) based GW method that employs frequency sampling to drastically reduce the computational effort when assessing quasiparticle states far away from the Fermi level is outlined. Compared to the canonical CD-GW method, computational scaling is reduced by an order of magnitude without sacrificing accuracy. This allows for an efficient calculation of core ionization energies. The improved computational efficiency is used to provide benchmarks for core ionized states, comparing the performance of 15 density functional approximations as Kohn–Sham starting points for GW calculations on a set of 65 core ionization energies of 32 small molecules. Contrary to valence states, GW calculations on core states prefer functionals with only a moderate amount of Hartree–Fock exchange. Moreover, modern ab initio local hybrid functionals are also shown to provide excellent generalized Kohn–Sham references for core GW calculations. Furthermore, the core–valence separated Bethe–Salpeter equation (CVS-BSE) is outlined. CVS-BSE is a convenient tool to probe core excited states. The latter is tested on a set of 40 core excitations of eight small inorganic molecules. Results from the CVS-BSE method for excitation energies and the corresponding absorption cross sections are found to be in excellent agreement with those of reference damped response BSE calculations. [ABSTRACT FROM AUTHOR]

Using fluorescence spectroscopy, the two-photon absorption cross sections of aqueous solutions of the styryl dye trans-4-[4-(dimethylamino)styryl]-1-methylpyridinium iodide (DASPI) and its inclusion complexes with cucurbit[n]urils (CB[n] n = 6–8) have been measured. A nonmonotonic dependence of the cross section on the excitation wavelength and on the cavitand cavity size has been revealed. Compared to the free dye, a sevenfold increase in the two-photon absorption cross section has been observed in DASPI inclusion complexes with CB[8] at an excitation wavelength of 980 nm. [ABSTRACT FROM AUTHOR]

Zirconium carbide (ZrC) ceramics have a high melting point, low neutron absorption cross section, and excellent resistance to the impact of fission products and are considered to be one of the best candidate materials for fourth-generation nuclear energy systems. ZrC ceramics with a high relative density of 99.1% were successfully prepared via pressureless sintering using a small amount of MoSi2 as an additive. The influence of the MoSi2 content on the densification behavior, microstructure, mechanical properties, and thermal properties of ZrC ceramics was systematically investigated. The results show that the densification of ZrC was significantly enhanced by the introduction of MoSi2 due to the formation of a liquid phase during sintering. In addition, the ZrC grains were refined due to the pinning effect of the generated silicon carbide. The flexural strength and Vickers hardness of ZrC ceramics with 2.5 vol% MoSi2 sintered at 1850 °C were 408 ± 12 MPa and 17.1 GPa, respectively, which were approximately 30% and 10% higher compared to the samples without the addition of MoSi2. The improved mechanical properties were mainly attributed to the high relative density (99.1%) and refined microstructure. [ABSTRACT FROM AUTHOR]

Long-term measurements of the mass concentration of black carbon (BC) in the atmosphere (MBC) with well-constrained accuracy are indispensable to quantify its emission, transport, and deposition. The aerosol light absorption coefficient (babs), usually measured by a filter-based absorption photometer, including an Aethalometer (AE), is often used to estimate MBC. The measured babs is converted to MBC by assuming a value for the mass absorption cross section (MAC). Previously, we derived the MAC for AE (MAC (AE)) from measured babs and independently measured MBC values at two sites in the Arctic. MBC was measured with a filter-based absorption photometer with a heated inlet (COSMOS). The accuracy of the COSMOS-derived MBC (MBC (COSMOS)) was within about 15%. Here, we obtained additional MAC (AE) measurements to improve understanding of its variability and uncertainty. We measured babs (AE) and MBC (COSMOS) at Alert (2018–2020), Barrow (2012–2022), Ny-Ålesund (2012–2019), and Pallas (2019–2022). At Pallas, we also obtained four-wavelength photoacoustic aerosol absorption spectrometer (PAAS-4λ) measurements of babs. babs (AE) and MBC (COSMOS) were tightly correlated; the average MAC (AE) at the four sites was 11.4 ± 1.2 m2 g−1 (mean ± 1σ) at 590 nm and 7.76 ± 0.73 m2 g−1 at 880 nm. The spatial variability of MAC (AE) was about 11% (1σ), and its year-to-year variability was about 18%. We compared MAC (AE) in the Arctic with values at mid-latitudes, measured by previous studies, and with values obtained by using other types of filter-based absorption photometer, and PAAS-4λ. Copyright © 2024 American Association for Aerosol Research [ABSTRACT FROM AUTHOR]

Quantifying the optical extinction cross section of a single plasmonic nanoparticle (NP) has recently emerged as a powerful method to characterize the NP morphometry, i.e., size and shape, with a precision comparable to electron microscopy while using a simple optical microscope. Here, we enhance the capabilities of extinction microscopy by introducing a high numerical aperture annular illumination coupled with a radial polarizer to generate a strong axial polarization component. This enables us to probe the NP response to axial polarized light, and, in turn, to distinguish flat-lying nanoplates from other geometries. Polarization-resolved optical extinction cross sections were acquired on 219 individual colloidal silver NPs of a nominally triangular nanoplate shape but, in practice, exhibiting heterogeneous morphometries, including decahedrons and non-plate spheroids. An unsupervised machine learning cluster analysis algorithm was developed, which allowed us to separate NPs into different groups, owing to the measured differences in cross sections. Comparison of the measurements with a computational model of the absorption and scattering cross section accounting for nanoplates of varying geometries beyond simple triangles provided insight into the NP shape of each group. The results provide a significant improvement of polarization-resolved optical extinction microscopy to reconstruct NP shapes, further boosting the utility of the method as an alternative to electron microscopy analysis. [ABSTRACT FROM AUTHOR]

Comparisons between total ozone column (TOC) measurements from ground-based Dobson and Brewer spectrophotometers and from various satellite instruments generally reveal seasonally varying differences of a few percent. A large part of these differences has been attributed to the operationally used Bass and Paur ozone cross sections and the lack of accounting for varying stratospheric temperatures in the standard total ozone retrieval for Dobson. This paper demonstrates how the use of new ozone absorption cross sections from the University of Bremen (Weber et al., 2016), as recommended by the Absorption Cross Sections of Ozone (ACSO) committee; the application of appropriate slit functions, especially for the Dobson instrument (Bernhard et al., 2005); and the use of climatological values for the effective ozone layer temperature (Teff), e.g., from TEMIS (Tropospheric Emission Monitoring Internet Service), essentially eliminate these seasonally varying differences between Brewer and Dobson total ozone data (to generally less than ±0.5 %). For Hohenpeissenberg, the previous seasonal difference (close to 0 % in summer and up to 2.5 % in winter) is reduced to less than ±0.5 % year-round. Implementing this approach to the existing global network of Dobson spectrometers will reduce the overall uncertainty in their total ozone data from 3 % to 4 % previously to under 2 % at most locations. [ABSTRACT FROM AUTHOR]

Ytterbium ion doped calcium niobium gallium garnet crystal (Yb: Ca3 (NbGa)5 O12) was successfully grown by Bridgman method. The structure of the crystal was analyzed by XRD. The crystal is cubic crystal system, and the unit cell parameter a = b = c = 12.471 Å. The crystal was tested by Raman spectroscopy, transmission spectroscopy, absorption and emission spectroscopy, and fluorescence lifetime. The absorption cross section, emission cross section, and gain cross section of the crystal were calculated. The effects of annealing in air on the absorption spectrum, emission spectrum and fluorescence lifetime of the crystal were studied. The absorption cross section at 935 nm before annealing is 1.82 x 10-20 cm², and it decreases to 1.40 x10-20 cm² after annealing. The emission cross section at 1 031 nm before annealing is 0.56 x10-20 cm² and it decreases to 0.40 x 10-20 cm² after annealing. The fluorescence decay time before annealing is 1.42 ms, and it is 1.32 ms after annealing. The results demonstrate that the annealing of Yb:Ca3 (NbGa)5 O12 single crystal in air will adversely affect the laser performance of the crystal.Yb:Ca3(NbGa)5O12 crystal. [ABSTRACT FROM AUTHOR]

The equation-of-motion coupled-cluster singles and doubles method with double electron attachment (EOM-DEA-CCSD) is capable of computing reliable energies, wave functions, and first-order properties of excited states in diradicals and polyenes that have a significant doubly excited character with respect to the ground state, without the need for including the computationally expensive triple excitations. Here, we extend the capabilities of the EOM-DEA-CCSD method to the calculations of a multiphoton property, two-photon absorption (2PA) cross sections. Closed-form expressions for the 2PA cross sections are derived within the expectation-value approach using response wave functions. We analyze the performance of this new implementation by comparing the EOM-DEA-CCSD energies and 2PA cross sections with those computed using the CC3 quadratic response theory approach. As benchmark systems, we consider transitions to the states with doubly excited character in twisted ethene and in polyenes, for which EOM-EE-CCSD (EOM-CCSD for excitation energies) performs poorly. The EOM-DEA-CCSD 2PA cross sections are comparable with the CC3 results for twisted ethene; however, the discrepancies between the two methods are large for hexatriene. The observed trends are explained by configurational analysis of the 2PA channels. [ABSTRACT FROM AUTHOR]

Mixed ionic–electronic conductor materials are exploited in energy storage and conversion applications, and, more recently, in emerging ionic thin film devices with distinctive electronic and optical functionalities, that impels studying their properties and, in particular, electrical transport mechanisms. Electrical and optical characterization methods, for instance, relaxation experiments under a small step variation in the mobile ion activity, are routinely used to study transport properties of mixed ionic–electronic conductors. In this work, we develop a theoretical basis for a synchronous electro-optical characterization method that enables fast measurement of the ionic and electronic (small polaron) mobilities, absorption cross section, and defect concentration in mixed ionic–electronic conductors with hopping transport. [ABSTRACT FROM AUTHOR]

Oxyfluoride transparent glass‐ceramics (GC) are widely used as the matrix for rare‐earth (RE) ions due to their unique properties such as low phonon energy, high transmittance, and high solubility for RE ions. Tb3+ doped oxyfluoride glasses exhibit a large absorption cross section for ultraviolet (UV) excitation, high stability, high photoluminescence quantum efficiency, and sensitive spectral conversion characteristics, making them promising candidate materials for use as the spectral converter in UV photodetectors. Herein, a Tb3+ doped oxyfluoride GC is developed by using the melt‐quenching method, and the microstructure and optical properties of the GC sample are carefully investigated. By combining with a Si‐based photo‐resistor,a solar‐blind UV detector is fabricated, which exhibits a significant photoelectric response with a broad detection range from 188 to 400 nm. The results indicate that the designed UV photodetector is of great significance for the development of solar‐blind UV detectors. [ABSTRACT FROM AUTHOR]

We describe an approach to incorporating the physical effects of the absorption of energy by the event horizon of black holes in the scattering amplitudes based post-Minkowskian, point-particle effective description. Absorptive dynamics are incorporated in a model-independent way by coupling the usual point-particle description to an invisible sector of gapless internal degrees-of-freedom. The leading order dynamics of this sector are encoded in the low-energy expansion of a spectral density function obtained by matching an absorption cross section in the ultraviolet description. This information is then recycled using the scattering amplitudes based Kosower-Maybee-O'Connell in-in formalism to calculate the leading absorptive contribution to the impulse and change in rest mass of a Schwarzschild black hole scattering with a second compact body sourcing a massless scalar, electromagnetic or gravitational field. The results obtained are in complete agreement with previous worldline Schwinger-Keldysh calculations and provide an alternative on-shell scattering amplitudes approach to incorporating horizon absorption effects in the gravitational two-body problem. [ABSTRACT FROM AUTHOR]

In this work, the quasinormal mode, greybody factors, and absorption cross section of de Sitter Reissner‐Nordström black hole surrounded by quintessence field in Rastall gravity are studied. The violation of energy‐momentum conservation has a non‐linear effect on the quasinormal modes. With an increase in the black hole charge, both real parts of quasinormal modes i.e. oscillation frequency of ring‐down Gravitational Waves (GWs) and damping or decay rate of GWs increase non‐linearly. A similar observation is made for the black hole structural parameter also, however in this case the variation is almost linear. The remnant mass of a black hole depends on different physical parameters of a black hole. In the case of greybody factors also, both parameters have similar impacts are observed. With an increase in these parameters, greybody factors decrease. Moreover, the null geodesics and the impact of Rastall gravity on the light trajectory are also investigated. Our study suggests that the presence of a surrounding quintessence field may shadow the existence of black hole charges in such black hole configurations. [ABSTRACT FROM AUTHOR]

In this paper, Er3+ doped TeO 2 -ZnF 2 -BaF 2 -KF-Ta 2 O 5 tellurite glasses with low hydroxyl content (∼0.03 × 10−19 cm−3) were investigated employing both glass composition and glass melting process optimization. The Raman spectra and physical properties were characterized to analyze the structure of the glasses. Under the pumping of 980 nm LD laser, intense up-conversion fluorescence at 1.5 and 2.7 μm of samples and their lifetimes were detected and analyzed, and the related transition mechanisms with gradient-varying Er3+ doping concentrations were discussed. The maximum absorption and emission cross section at 2.7 μm was calculated to be 6.4 × 10−21 cm2 and 6.8 × 10−21 cm2, correspondingly, which were higher than those of traditional tellurite glasses. Using the calculated and measured spectroscopic parameters of bulk tellurite glass, a dual-wavelength pumping model was established to verify the feasibility of mid-infrared laser output in similar tellurite glass fiber. Experimental results support the assertion that the Er3+ doped tellurite glasses hold promise as a candidate laser gain medium for mid-infrared fiber laser systems. [ABSTRACT FROM AUTHOR]

The photoluminescence spectra of the dominant H3 and H4 centers in a natural diamond sample, which is preliminarily characterized by optical and infrared spectrophotometry, are excited by femtosecond laser pulses with a wavelength of 470 nm and varying intensity. Saturation of the photoluminescence intensity of the H3 and H4 centers normalized by the intensity of laser radiation is observed and attributed to the saturation of the resonance transition responsible for the excitation. This makes it possible for the first time to estimate the absorption cross sections of H3 and H4 centers, which can be compared with values known from the literature and those determined from photoluminescence kinetics. The total concentration of H3 and H4 centers can then be found. Taking into account the known absorption coefficient of the sample at a wavelength of 470 nm and the previously established ratio of the contributions from H3 and H4 centers, their concentrations have been estimated separately for the first time. [ABSTRACT FROM AUTHOR]

LiH is valued by researchers and engineers for its high-temperature resistance, high strength, high hydrogen storage capacity of up to 12.6 wt%, and high neutron absorption cross section. However, sintering and application of this material are difficult. Lithium hydride is a highly effective neutron shielding material. The neutron shielding ability of lithium hydride is directly affected by the homogeneity of the total amount and distribution of hydrogen. The heat migration of hydrogen reduces the neutron shielding effectiveness of lithium hydride. It is critical to forecast H's diffusion behavior. The diffusion coefficient is a critical metric for determining the diffusion efficiency. As a result, the stability, electronic structure, and bonding properties of LiH, LiOH, and H entering the tetrahedral interstitial sites of LiH were calculated using first principles based on density functional theory (DFT). The elastic modulus of the system was also examined to find the lowest thermal conductivity, and some thermodynamic parameters were derived by calculating LiH phonons. Finally, static calculations were used to determine the diffusion coefficient and diffusion activation energy of H in the LiH solid solution. The results revealed that the addition of H altered the characteristics of the LiH semiconductor, giving it metallic features. The lowest thermal conductivity of the LiH system was 2.9. W·m−1 K−1. The diffusion coefficient was D = (2.638 × 10 − 2 c m 2 / s ) exp ( − 5.811 × 10 − 3 cal / K B T). The activation energy for diffusion was 0.252 eV. The diffusion coefficients, elastic constants, and lattice parameters all corresponded well with previously published results. The density functional theory was employed to study the material's system energy and electrical structure, and the microscopic migratory behavior of hydrogen was predicted theoretically. The calculation of the lowest thermal conductivity provided a reference for the screening of ceramic materials. • First-principles calculations can allow for a better understanding of the H diffusion mechanism in LiH materials. • Diffusion from the LiH surface to the interior of the material requires greater energy drive. • The introduction of interstitial H atoms can make LiH have metal properties. • The lowest thermal conductivity of the material can provide a reference for the selection of ceramic materials. • LiOH is more thermally stable than LiH. [ABSTRACT FROM AUTHOR]

Oxazolones or azlactones are small heterocyclic systems that can be easily functionalized with a double bond directly attached to their structure. In addition, they can be substituted on the opposite side of the heterocycle with styrenyl groups to extend their conjugation. This allows for versatile tuning of their linear and non‐linear optical properties. In this work, eight doubly substituted oxazolones including different push‐pull or pull‐pull designs were synthesized, and their linear and non‐linear photophysical properties were studied. As we show, the two‐photon activity of these systems is dependent on the donor‐acceptor pattern, where a methoxy substitution on the styrene end of the molecule and an acetyl group on the other end shows two‐photon Z‐E conversion properties with an important two photon absorption cross section of 308 GM. Most oxazolones shown in this study undergo picosecond relaxation to the electronic ground state, releasing the biphotonic energy to their surrounding environment. The results obtained in this work are indicative of potential applications of these molecules in schemes where high spatial patterning or thermalization is required. [ABSTRACT FROM AUTHOR]

Accelerating space–time is commonly utilized to depict the formation of pairs of black holes. This paper studies the pair production of charged scalar particles in the vicinity of an accelerating Reissner–Nordstrom black hole's event horizon. Essentially, we aim to investigate the production of particles that accompanies the creation of black hole pairs. In a near extremal state, this pair production manifests as a combination of Hawking radiation and the Schwinger effect. Under extremal conditions, only the latter effect remains. Furthermore, this research explores the influence of the acceleration parameter on the absorption cross section of scalar particles in proximity to the black hole. [ABSTRACT FROM AUTHOR]

High‐sensitivity photodetection capability has become an indispensable requirement for detecting feeble solar‐blind ultraviolet (UV) light. Micro‐nano metallic metasurface structures are employed to enhance the detector photoelectric performances. However, existing approaches are confronted with bottlenecks of structure simplification and efficacy mediocrity. Here, a distinctive diamond solar‐blind UV photodetector with a synthetic multistage‐concentric‐annulus (MCA) architecture metasurface is reported, which is prepared through a facile and peculiar Fraunhofer diffraction technique. The detector achieves an excellent photo‐to‐dark‐current ratio of 2.4×108 and maintains an extremely low dark current on the order of pA magnitude. The intrinsic response peak and resonance absorption phenomenon in solar‐blind UV are evident from the optical properties. Moreover, the surface potential distribution intuitively reveals that plasmon resonance enhances the UV scattering and absorption cross sections, thus facilitating the photogeneration of carriers. Meanwhile, it expressly demonstrates that multi‐level dipole interaction in the MCA structure accelerates the separation and extraction of electron–hole pairs through enhancing the localized electric field intensity. In addition, a wide range of variable temperature measurements further prove the device possesses capacity for working in extreme environments. This photodetection technology by virtue of a delicate and viable diffraction metasurface is anticipated to provide a leap forward for future applications in wide‐band‐gap semiconductor UV detectors. [ABSTRACT FROM AUTHOR]

Herein, a facile, catalyst-free, and dry topochemical transformation strategy for transforming the Bi2S3 nanowires to the Bi2Se3 nanowires, which has been realized through an atmospheric pressure high-temperature selenization treatment, has been developed. The complete topochemical transformation has been verified by combining x-ray diffraction, Raman spectroscopy, energy dispersive spectrometer, x-ray photoelectron spectroscopy, transmission electron microscopy, and selected area electron diffraction measurements. Systematical optical characterizations, including polarization-resolved optical microscopy images and polarization-dependent Raman spectra, have revealed the strong anisotropy of the Bi2Se3 nanowires. Furthermore, finite-different time-domain simulations have consolidated that the Bi2Se3 nanowires possess highly anisotropic absorption cross sections across the ultraviolet to far infrared spectral range, laying a solid foundation for the realization of ultra-broadband polarized optoelectronic applications. On the whole, this pioneering study depicts a unique avenue for topological material design accompanied with the integration of additional functionalities beyond the intrinsic counterparts, opening up an attractive research field for polarized photonics and optoelectronics. [ABSTRACT FROM AUTHOR]

The correct interpretation of infrared (IR) observations of planetary atmospheres requires an accurate knowledge of temperature and partial and global pressures. Precise laboratory measurements of absorption intensities and line profiles, in the 200–350 K temperature range, are, therefore, critical. However, for gases only existing in complex chemical equilibria, such as nitrous or hypobromous acids, it is not possible to rely on absolute pressure measurements to measure absolute integrated optical absorption cross sections or IR line intensities. To overcome this difficulty, a novel dual-beam terahertz (THz)/mid-IR experimental setup has been developed, relying on the simultaneous use of two instruments. The setup involves a newly constructed temperature-controlled (200–350 K) cross-shaped absorption cell made of inert materials. The cell is traversed by the mid-IR beam from a high-resolution Fourier transform spectrometer using along a White-cell optical configuration providing absorption path lengths from 2.8 to 42 m and by a THz radiation beam (82.5 GHz to 1.1 THz), probing simultaneously the same gaseous sample. The THz channel records pure rotational lines of molecules for which the dipole moment was previously measured with high precision using Stark spectroscopy. This allows for a determination of the partial pressure in the gaseous mixture and enables absolute line intensities to be retrieved for the mid-IR range. This new instrument opens a new possibility for the retrieval of spectroscopic parameters for unstable molecules of atmospheric interest. The design and performance of the equipment are presented and illustrated by an example of simultaneous THz and mid-IR measurement on nitrous acid (HONO) equilibrium. [ABSTRACT FROM AUTHOR]

Calculated rocking curves are presented for the spectrometric scheme of a double-crystal diffractometer made of InSb crystals in the Laue–Laue geometry for neutron wavelength ranges corresponding to the weak potential and strong resonant absorptions. The appearance and shape of the curves calculated using the extended expression with allowance for the absorption cross section and the curves obtained using the Compton–Alisson expression are compared. [ABSTRACT FROM AUTHOR]

The paper considers the methodological aspects of experiments planning on the irradiation of experimental fuel rods of a VVER-SKD reactor and analyzes the features of the concept of sequential irradiation in fast and thermal reactors. It is shown that the 149Sm accumulated at the irradiation in the BOR-60 plays the role of a burnable absorber at the initial stage of irradiation in the reflector cell of the IR-8 reactor. This absorber quickly burns out owing to large absorption cross section and its concentration gradually comes to equilibrium. Burnup of 149Sm leads to a gradual increase in the linear load of the irradiated experimental fuel rod, followed by a decrease and reaching the equilibrium irradiation regime. This effect must be considered when planning the irradiation regime for experimental fuel elements of the VVER-SKD reactor. [ABSTRACT FROM AUTHOR]

DFB diode laser at 1434 nm was used to detect the hydroxyl radical OH in the first overtone region. Experiments were made at the most intense line Q(3/2) of 2Π3/2 electronic term. Collisional broadening for He buffer gas was measured. Using reliably defined integrated intensity of this line and calculated line contour, the absorption cross section could be obtained for different pressures. This enables measurement of the absolute concentration of OH in time-resolved experiments without calibration. The minimum concentration of radicals detected by absorption is 2 × 1012 cm–3 with the resolving time approximately 10–6 s. [ABSTRACT FROM AUTHOR]

By comparing the results of calculations using the Mie theory, which is considered exact, a validity region of the approximate method for calculating the extinction cross section of spherical nanoparticles through polarizability has been found. The calculations were performed for w-CdS, InP, and PbS, and their results were presented in the form of the exact extinction cross section to the approximate absorption cross section ratio as a function of the particle size and light wavelength. The extinction coefficients for w-CdS and PbS nanoparticles depending on the wavelength and refractive index of the medium have also been calculated. [ABSTRACT FROM AUTHOR]

Laser-based optical diagnostic tools are widely used to investigate in-cylinder processes in internal combustion engines. For laser-induced fluorescence (LIF), many tracers have been used in the past. Recently, anisole has been characterized spectroscopically for engine-relevant pressures and temperatures and emerged as a potentially advantageous alternative to more commonly used tracers in the past due to its photo-physical properties. Its high fluorescence quantum yield and large absorption cross section result in high signal intensity. This is particularly beneficial for endoscopic imaging systems, which typically have worse light collection efficiency than traditional imaging systems in fully optically accessible engines with transparent liners. In this work, we exploited the strong anisole LIF signal in two single-shot experiments: to image flame propagation, and the instantaneous gas-phase temperature during compression stroke and gas exchange process. Measurements were performed in a production gasoline engine modified for endoscopic optical access via an advanced UV endoscope system. First, LIF of anisole was compared to that of toluene during compression stroke. Anisole LIF yields a much higher signal-to-noise ratio and better image quality with lower tracer concentrations. Due to the higher signal of anisole LIF, small structures of the turbulent flame burning into the anisole/isooctane mixture were well visible after ignition. Second, the red-shift of the anisole fluorescence spectrum with increasing temperature and oxygen partial pressure was exploited for ratiometric temperature measurements based on single-shot images. The available spectroscopic data were used to develop several signal ratio models, which were calibrated in situ using a heated tracer/bath gas mixture introduced inside the combustion chamber. The calibrated signal ratio models were then extrapolated to the engine-relevant ranges. Models with two-step exponential interpolation show better agreement with the adiabatic temperature than linear or 3D surface exponential interpolation. The gas-phase temperature images based on single shots were obtained using one selected model, showing a near uniform and a stratified temperature distribution during the compression stroke and gas exchange process, respectively. [ABSTRACT FROM AUTHOR]

Comparison of total ozone column (TOC) measurements from ground-based Dobson and Brewer spectrophotometers and from various satellite instruments generally reveals seasonally varying differences of a few percent. A large part of these differences has been attributed to the operationally used Bass & Paur ozone cross-sections and the lack of accounting for varying stratospheric temperatures in the standard total ozone retrieval for Dobson. This paper demonstrates how the use of new ozone absorption cross sections from the University of Bremen (Weber et al., 2016), as recommended by the committee on Absorption Cross-Sections of Ozone, the application of appropriate slit functions, especially for the Dobson instrument (Bernhard et al. 2005), and the use of climatological values for the effective ozone layer temperature (Teff), e.g. from TEMIS, essentially eliminate these seasonally varying differences between Dobson and Brewer total ozone data. Applying this approach to the existing global network of Dobson spectrometers will reduce the uncertainty of their total ozone data, from previously 3 to 4% to better than 2.0% at most locations. [ABSTRACT FROM AUTHOR]

Electron and positron impact elastic scattering Differential Cross Section (DCS), Momentum Transfer Cross Section (MTCS), Integrated Elastic Cross Section (IECS), Viscosity Cross Section (VCS) and Absorption Cross Section (ABSCS) are reported in the energy range from 10 to 20,000 eV. The elastic DCS, IECS, MTCS, VCS, and ABSCS for the ground state of the Pb atom are obtained in the Dirac Partial-Wave analysis approach using the optical-model potential for target and relativistic partial wave calculation for the projectile (electron & positron). The present results for the electron scattering are compared with the available experimental and theoretical results. Reasonable agreement with the available experimental and theoretical results is obtained. [ABSTRACT FROM AUTHOR]

Upconverter/MoS2 heterostructure thin films fabricated by hydrothermal technique are confirmed by X‐ray diffraction and Raman studies. Field‐emission scanning electron microscopy (FESEM) and high‐resolution transmission electron microscopy (HRTEM) reveal the nanobelt structured MoS2 mingled with trapezoid structure fluoride upconverters and sphere‐shaped oxide upconverters. The films exhibit green (H11/22 to I15/24) and red (F9/24 to I15/24) emission. The influence of upconverters on the nonlinear absorption of MoS2 is exploited by Z‐scan technique using nanopulsed laser. Estimated ground‐state absorption cross section is higher than the excited‐state absorption cross section of the samples and it confirms the occurrence of saturable absorption. CeO2:Yb,Er@MoS2 exhibits stronger saturable absorption due to synergetic effects like higher linear absorption coefficient at 532 nm, stronger green emission, and reduced size. Results pave way for the design of optical switches, Q‐switches, and mode lockers using upconverter integrated MoS2 thin films. [ABSTRACT FROM AUTHOR]

A comparison between storm‐time TIMED/GUVI FUV spectra in thermospheric composition disturbed (O/N2 <∼140 km> depleted and NO <∼110 km> enhanced) and undisturbed regions reveals the following features: (1) A clear decrease in N2 LBHS (140–150 nm) band intensities compared to that between 150 and 160 nm; (2) A significant spectral decrease around O 164.1 nm; (3) Two enhanced peaks between 170 and 185 nm. The feature (2) is clearly due to atomic oxygen density decrease in the low thermosphere. The feature (3) is caused by storm‐time production and transport of nitric oxide. An AURIC simulation reproduced feature (1) confirming that storm‐time enhancement in O2 density (∼120–170 km) and the wavelength dependent O2 absorption cross section are the source of observed feature (1). On the other hand, the feature (1) was not observed in the regions without O/N2 depletion. This further supports that O2 density enhancement is responsible for feature (1). Plain Language Summary: Observations by a FUV spectrograph imager on NASA TIMED satellite revealed two interesting features in the storm‐time disturbed thermosphere: (1) a relative decrease in N2 LBH intensities at 140–150 nm versus 150–160 nm, (2) significant decrease in O 164.1 nm radiance and enhanced emission between 170 and 185 nm. The feature (2) is well known and due to O density depletion and production of nitric oxide. The feature is not well understood. A model simulation indicates the feature (1) is due to storm‐time O2 density increase and wavelength dependent O2 absorption cross section which peaked around 140 nm. This result indicates that FUV spectrograph imager is capable to detect storm‐time O2 density changes. Key Points: (1) FUV spectral difference between storm‐quiet time shows a relative decrease in N2 LBH intensities at 140–150 nm versus 150–160 nmThe FUV spectrograph difference between undisturbed regions did not show the above feature(3) Simulations confirm indicate that enhanced O2 density and absorption causes the observed FUV spectral differences [ABSTRACT FROM AUTHOR]

A systematic investigation was carried out on the elastic scattering of low- to intermediate-energy electrons ( E 0 = 0.1–1000 eV eV) by acetonitrile (CH3CN). We calculated differential (DCS), integral (ICS), momentum-transfer (MTCS), and total absorption cross sections from 0.1 to 1000 eV energy range using an absorption-effects-implemented ePolyScat-E3 suite of codes, which applies the Schwinger variational method combined with the Padé-approximants technique. Also, the screen-corrected independent atom model was used to compute DCSs, ICSs, and MTCSs from 10–1000 eV impact energies. Present results are compared to other theoretical and experimental data when available. In general, our DCS and MTCS results show a good agreement with available data, however, the ICSs and the resonance features exhibit fair accordance. Our results show two shape-resonance structures: one at about 3.4 eV and a second at about 7 eV. They are labeled as π ∗ and σ ∗ , and comprise the 2 E and 2 A 1 scattering channels, respectively. [ABSTRACT FROM AUTHOR]

This paper aims to investigate the different properties of cobalt-doped and undoped tin oxide thin films. The tin oxide thin films were doped with different atomic percentages of cobalt, ranging from 0% (undoped) to 2% and 4%, using a cost-effective and easily accessible technique known as spray pyrolysis with a moving nozzle at 490 °C. The phase identification of the different thin layers was carried out using X-ray diffraction, which indicated that the compound is homogeneous has a polycrystalline structure and is, with preferential orientation growth at the (211) level. The optical properties of the synthesized thin films were investigated using UV-visible spectroscopy in the range from 300 to 900 nm, which allowed the estimation of both linear and nonlinear optical properties. The results of the investigations into the linear optical properties indicated that the samples have a direct band gap energy between 3.75 to 3.81 eV, permittivity between 2.67 to 3.266, photoelectrons between 0.2 to 3.35 = 1025, and refractive index between 1.778 to 1.875. The results also indicated that the absorption cross section changes with photon energy and the number of photoelectrons, where it has an approximately constant value at low energies. Moreover, the nonlinear optical properties were determined using the Sheik-Bahae model, which revealed that the samples have the same maximum two-photon absorption (TPA) process coefficient of 3.63 cm/W and the same maximum nonlinear refractive index (NRI) value of 6.91 × 10−8 cm2/W. [ABSTRACT FROM AUTHOR]

A boron-rich boron–carbide material (B4+δC) was synthesized by spark plasma sintering of a ball-milled mixture of high-purity boron powder and graphitic carbon at a pressure of 7 MPa and a temperature of 1930 °C. This high-pressure, high-temperature synthesized material was recovered and characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, Vickers hardness measurements, and thermal oxidation studies. The X-ray diffraction studies revealed a single-phase rhombohedral structure (space group R-3m) with lattice parameters in hexagonal representation as a = 5.609 ± 0.007 Å and c = 12.082 ± 0.02 Å. The experimental lattice parameters result in a value of δ = 0.55, or the composition of the synthesized compound as B4.55C. The high-resolution scans of boron binding energy reveal the existence of a B-C bond at 188.5 eV. Raman spectroscopy reveals the existence of a 386 cm−1 vibrational mode representative of C-B-B linear chain formation due to excess boron in the lattice. The measured Vickers microhardness at a load of 200 gf shows a high hardness value of 33.8 ± 2.3 GPa. Thermal gravimetric studies on B4.55C were conducted at a temperature of 1300 °C in a compressed dry air environment, and its behavior is compared to other high-temperature ceramic materials such as high-entropy transition metal boride. The high neutron absorption cross section, high melting point, high mechanical strength, and thermal oxidation resistance make this material ideal for applications in extreme environments. [ABSTRACT FROM AUTHOR]

We investigate molecular plasmonic excitations sustained in hollow spherical gold nanoparticles using time-dependent density functional theory (TD-DFT). Specifically, we consider Au60 spherical, hollow molecules as a toy model for single-shell plasmonic molecules. To quantify the plasmonic character of the excitations obtained from TD-DFT, the energy-based plasmonicity index is generalized to the framework of DFT, validated on simple systems such as the sodium Na20 chain and the silver Ag20 compound, and subsequently successfully applied to more complex molecules. We also compare the quantum mechanical TD-DFT simulations to those obtained from a classical Mie theory that relies on macroscopic electrodynamics to model the light–matter interaction. This comparison allows us to distinguish those features that can be explained classically from those that require a quantum-mechanical treatment. Finally, a double-shell system obtained by placing a C60 buckyball inside the hollow spherical gold particle is further considered. It is found that the double-shell, while increasing the overall plasmonic character of the excitations, leads to significantly lowered absorption cross sections. [ABSTRACT FROM AUTHOR]

The nonlinear optical limiting (OL) property of tin phthalocyanine porous organic frameworks (Sn-Pc-POFs) dispersion in the nanosecond regime was studied, which showed excellent dispersibility and stability as well as a low OL threshold. To clarify the nonlinear optical response mechanisms in the material, the energy level structure of Sn-Pc-POFs was simulated using the density functional theory calculation, and the photoinduced carrier dynamics was studied using femtosecond time-resolved transient absorption spectroscopy. The results indicated that the large absorption cross section and long lifetime of the excited state were responsible for the excellent OL property of the material. [ABSTRACT FROM AUTHOR]

Photon upconversion, particularly via triplet–triplet annihilation (TTA), could prove beneficial in expanding the efficiencies and overall impacts of optoelectronic devices across a multitude of technologies. The recent development of bulk metal halide perovskites as triplet sensitizers is one potential step toward the industrialization of upconversion-enabled devices. Here, we investigate the impact of varying additions of bromide into a lead iodide perovskite thin film on the TTA upconversion process in the annihilator molecule rubrene. We find an interplay between the bromide content and the overall device efficiency. In particular, a higher bromide content results in higher internal upconversion efficiencies enabled by more efficient charge extraction at the interface likely due to a more favorable band alignment. However, the external upconversion efficiency decreases as the absorption cross section in the near infrared is reduced. The highest upconversion performance is found in our study for a bromide content of 5%. This result can be traced back to a high absorption cross section in the near infrared and higher photoluminescence quantum yield in comparison to the iodide-only perovskite and an increased driving force for charge transfer. [ABSTRACT FROM AUTHOR]

Background-free detection of inherently weak chiroptical signals remains one of the great challenges in research communities and industries. We demonstrate coherent multipolar amplification of chiroptical responses via a magnetoelectric nanoparticle capped with an optically active monolayer encapsulated in a lossless background medium. Such an achiral nanoparticle can simultaneously support both electric and magnetic Mie-type resonances. We show how the combined excitation of orthogonal multipolar modes of the same order boosts the magnetoelectric coupling induced by the adsorbed chiral molecules, thus enabling coherently enhanced chiroptical responses from the ligand-capped magnetoelectric nanoparticle and allowing for absolute chirality measurements, in comparison with non-magnetoelectric nanoparticles. Furthermore, we develop rigorous expressions to separate relative contributions of chiral and nonchiral portions of circular differential absorption cross section, and analyzed the chirality-dependent far-field radiation patterns at different overlapped multipolar modes, providing a theoretical framework to understand the underlying enhancement mechanism of the magnetoelectric-assisted sensing of molecular chirality. Regular nanoparticles amplify the electric component of the radiating field, yet such amplification is generally insufficient to reveal the inherently weak chiral signal of molecules. By simultaneously exciting magnetic and electric modes of a coreshell magnetoelectric nanoparticle, the authors are able to strongly enhance the chiroptical response of the optically active medium. [ABSTRACT FROM AUTHOR]

We report on photoluminescence emission in copper iodide bulk single crystals induced by two- and three-photon absorption around 1.525 eV. These non-linear optical processes are investigated utilizing density-dependent, steady-state, as well as time-resolved photoluminescence spectroscopy as a function of the excitation energy. Using an excitation energy that corresponds to half of the bandgap energy, the observed photoluminescence intensity dependence on the excitation power shows an almost parabolic behavior. By further reduction of the photon energy, a cubic contribution is observable, which increases with decreasing excitation energy. The experimentally observed behavior can be well described by taking into account two- and three-photon absorption. By a simultaneous analysis of the intensity behavior for all used excitation energies, we determined a ratio between the two- and three-photon absorption cross section on the order of σ 0 (3) / σ 0 (2) ≈ 10 − 28 cm 2 s. [ABSTRACT FROM AUTHOR]

Background-free detection of inherently weak chiroptical signals remains one of the great challenges in research communities and industries. We demonstrate coherent multipolar amplification of chiroptical responses via a magnetoelectric nanoparticle capped with an optically active monolayer encapsulated in a lossless background medium. Such an achiral nanoparticle can simultaneously support both electric and magnetic Mie-type resonances. We show how the combined excitation of orthogonal multipolar modes of the same order boosts the magnetoelectric coupling induced by the adsorbed chiral molecules, thus enabling coherently enhanced chiroptical responses from the ligand-capped magnetoelectric nanoparticle and allowing for absolute chirality measurements, in comparison with non-magnetoelectric nanoparticles. Furthermore, we develop rigorous expressions to separate relative contributions of chiral and nonchiral portions of circular differential absorption cross section, and analyzed the chirality-dependent far-field radiation patterns at different overlapped multipolar modes, providing a theoretical framework to understand the underlying enhancement mechanism of the magnetoelectric-assisted sensing of molecular chirality. Regular nanoparticles amplify the electric component of the radiating field, yet such amplification is generally insufficient to reveal the inherently weak chiral signal of molecules. By simultaneously exciting magnetic and electric modes of a coreshell magnetoelectric nanoparticle, the authors are able to strongly enhance the chiroptical response of the optically active medium. [ABSTRACT FROM AUTHOR]

The scattering problem for a dimer consisting of a carbon nanotube (CNT) coated with a thick gold layer everywhere except for a narrow central region is solved in the far-IR range by numerical methods. The nanotube in such a dimer is a low-conductive channel that slows the flow of charges between the two parts of the highly conductive gold coating. Charge-transfer plasmon resonance arises at a frequency of 21 THz in the spectrum of the absorption cross section of a dimer with a length of 285 nm and a transverse size of 20 nm. The resonance width is determined by the electron relaxation time in the CNTs. The resonant frequency is shown to decrease and the absorption cross section at the resonant frequency, to increase with increases in the transverse and longitudinal dimensions of the dimer. The presence of contact resistance between the CNT and the gold layer leads to a shift of the resonant frequency to the low-frequency region and a decrease in the absorption peak intensity. The ability to vary the CNT conductivity by electrostatic doping makes it possible to use such dimers as building blocks for metamaterials with controlled resonant properties in the far-IR range. [ABSTRACT FROM AUTHOR]

The development of fluorescent probe for hydrazine (N2H4) detection has attracted much attention due to the important role of N2H4 plays in the fields of medicine, agriculture, biology and environments. In this paper, the optical properties and water solubility of two novel two-photon fluorescent molecular probes (Probe1 and Probe2) before and after the reaction with N2H4 are studied by using the density function theory. The results show that electronic distribution and transition dipole moment of the probes are obviously changed after the reaction with N2H4, thus the optical properties of the molecules are influenced and the detection of N2H4 are realized. In addition, photoinduced electron transfer processes for Probe1 and Probe2 in the presence of N2H4 are theoretically characterized, which explains the experimental observations from the microscopic mechanism. Special attention has been paid on the analysis of the two-photon absorption for the probes with the absence and presence of N2H4 by the response theory method. Both probes with good water solubility show large variation on the two-photon absorption cross section when reacts with N2H4. In particular, the two-photon absorption response of Probe2 is more obvious, so it possesses preferable two-photon fluorescence microscopic imaging ability. More importantly, the receptor effect on the sensing performances of the probes are demonstrated, providing a theoretical reference for the design and synthesis on more efficient two-photon fluorescence N2H4 probes. Our study provides necessary information on the response mechanism of the studied chemosensors and helps to establish the relationship between the structure and optical properties of two-photon fluorescence N2H4 probes. [ABSTRACT FROM AUTHOR]

Background: The light-harvesting antennae of photosystem (PS) I and PSII are pigment-protein complexes responsible of the initial steps of sunlight conversion into chemical energy. In natural environments plants are constantly confronted with the variability of the photosynthetically active light spectrum. PSII and PSI operate in series but have different optimal excitation wavelengths. The prompt adjustment of light absorption by photosystems is thus crucial to ensure efficient electron flow needed to sustain downstream carbon fixing reactions. Fast structural rearrangements equilibrate the partition of excitation pressure between PSII and PSI following the enrichment in the red (PSII-favoring) or far-red (PSI-favoring) spectra. Redox imbalances trigger state transitions (ST), a photoacclimation mechanism which involves the reversible phosphorylation/dephosphorylation of light harvesting complex II (LHCII) proteins by the antagonistic activities of the State Transition 7 (STN7) kinase/TAP38 phosphatase enzyme pair. During ST, a mobile PSII antenna pool associates with PSI increasing its absorption cross section. LHCII consists of assorted trimeric assemblies of Lhcb1, Lhcb2 and Lhcb3 protein isoforms (LHCII), several being substrates of STN7. However, the precise roles of Lhcb phosphorylation during ST remain largely elusive. Results: We inactivated the complete Lhcb1 and Lhcb2 gene clades in Arabidopsis thaliana and reintroduced either wild type Lhcb1.3 and Lhcb2.1 isoforms, respectively, or versions lacking N-terminal phosphorylatable residues proposed to mediate state transitions. While the substitution of Lhcb2.1 Thr-40 prevented the formation of the PSI-LHCI-LHCII complex, replacement of Lhcb1.3 Thr-38 did not affect the formation of this supercomplex, nor did influence the amplitude or kinetics of PSII fluorescence quenching upon state 1—state 2 transition. Conclusions: Phosphorylation of Lhcb2 Thr-40 by STN7 alone accounts for ≈ 60% of PSII fluorescence quenching during state transitions. Instead, the presence of Thr-38 phosphosite in Lhcb1.3 was not required for the formation of the PSI-LHCI-LHCII supercomplex nor for re-equilibration of the plastoquinone redox state. The Lhcb2 phosphomutant was still capable of ≈ 40% residual fluorescence quenching, implying that a yet uncharacterized, STN7-dependent, component of state transitions, which is unrelated to Lhcb2 Thr-40 phosphorylation and to the formation of the PSI-LHCI-LHCII supercomplex, contributes to the equilibration of the PSI/PSII excitation pressure upon plastoquinone over-reduction. [ABSTRACT FROM AUTHOR]

An analytical expression is obtained for the rocking curve of a double-crystal spectrometer, which does not require restrictions on the absorption cross section dependency on the wavelength. A modeled rocking curve (instrumental line) for the Bragg–Bragg spectrometric scheme is calculated using the example of an InSb crystal in the region of weak dependency between the absorption cross section and the wavelength and in the region of wavelengths close to the absorption resonance. [ABSTRACT FROM AUTHOR]

Nd:GdVO4 has the advantages of a small thermal expansion coefficient, a large absorption bandwidth, and a large absorption and emission cross section, making it a good gain material for LED-pumping without active temperature control. In this paper, the LED-pumped Nd:GdVO4 laser was first generated in the quasi-continuous-wave and the passively Q-switched regime. With the incident pump energy of 8.0 mJ, the Nd:GdVO4 laser demonstrated energy of 195 μJ at 1063 nm in the quasi-continuous-wave regime, the slope efficiency was 4.7%, and the optical conversion efficiency was 2.4%. In the passively Q-switched regime, Cr:YAG was used as a saturable absorber and the energy obtained was 6.53 μJ with a pulse duration of 806.8 ns. These experimental results indicated the application prospect of LED-pumped lasers. [ABSTRACT FROM AUTHOR]

Resonance fluorescence scattering is the physical mechanism with which lidar detects atmospheric metal layers. The resonance fluorescence scattering cross section is an important parameter for lidar data processing. In this work, the resonance fluorescence backscattering cross sections of most detectable metal atoms and ions in the atmosphere were calculated. The calculated maximum backscattering cross section of Na at the D2 line is 7.38 × 10−17 m2/sr; K at the D1 line is 7.37 × 10−17 m2/sr; Fe at the 372 nm line is 7.53 × 10−18 m2/sr; Fe at the 374 nm line is 6.98 × 10−18 m2/sr; Fe at the 386 nm line is 3.75 × 10−18 m2/sr; Ni at the 337 nm line is 4.05 × 10−18 m2/sr; and Ni at the 341 nm line is 2.05 × 10−17 m2/sr; Ca is 3.06 × 10−16 m2/sr; Ca+ is 1.12 × 10−16 m2/sr. The influence of the laser linewidth on the effective scattering cross section was discussed. If the laser linewidth is lower than 2 GHz to detect Na, the laser center frequency locked at the D2a line is a better option than the D2 line in order to obtain greater signals. If an unlocked lidar is used to detect Na, the frequency at D2a should be used as the laser center frequency when the effective scattering cross section of Na was calculated, because the absorption cross section of Na atom has two local maxima. This work proposes a quantifiable comparative method for assessing the observation difficulty of different metal particles by comparing their relative uncertainties in lidar observation. It is assumed that under the same observation conditions, the detectability of different metal atoms and ions is compared. Using Na as a basis for comparison, the relative uncertainty of Ni at 337 nm is the highest, about a factor of 21 larger than that of Na, indicating that it is the most difficult to be detected. The purpose of this work is to present a quantifiable comparison method for the detection difficulty of the metal particles by lidar in the middle and upper atmosphere, which has great significance for the design of the lidar system. [ABSTRACT FROM AUTHOR]