Spectral Characteristics Of Radiation Research Articles

Conversion of spectral characteristics of laser radiation in periodic domain structures written by the electron-beam method in planar waveguides formed by Ti diffusion in Y-oriented LiNbO3

Periodic domain structures for nonlinear conversion of spectral characteristics of laser radiation in the planar Ti : LiNbO3 waveguide have been formed by the method of electron-beam writing. Domain gratings with a spatial period of 6.50 μm formed in the Y-cut plate over a wide range of accelerating voltages have been visualised by the method of second harmonic generation microscopy (SHG-microscopy) in transmitting geometry and at waveguide excitation. It is found that the domain structure written at an accelerating voltage of 10 kV in a waveguide with an exponential refractive index profile and an effective thickness of 1.75 μm is characterised by high homogeneity. It is composed of continuous domain rows and provides near-quasi-phase-matching radiation conversion at a wavelength of 1053 nm into the second harmonic for the TE0 → TE1 waveguide process.

The relationship between surface spectral albedo and soil moisture in an arid Gobi area

Surface albedo is one of the most important properties of underlying surface. However, errors still exist in the calculation of the surface albedo because of complex influencing factors. Understanding the relationship between the surface albedos in different wavebands, and soil moisture will provide theory basis for the parameterization of surface albedos. In this paper, using the data on the spectral radiation and soil moisture observation in Dunhuang, China, from August to October 2016, the spectral radiation characteristics of the underlying surface in this arid Gobi area, the variation characteristics of the surface spectral albedo and its relationship with 2-cm soil moisture were analyzed. The results show that the decrease of the angle of the sun due to seasonal change is the reason of the decrease of NIR, GR, VIS, and UV. The surface albedos in different wavebands are affected by the surface soil moisture, and they exhibit obvious anti-correlations. During the observation period, the average surface albedo of NIR, GR, VIS, and UV is 0.263, 0.230, 0.204, and 0.096, respectively, while the correlation coefficient with 2-cm soil moisture is − 0.522, − 0.678, − 0.804, and − 0.812, respectively. When solar altitude is larger than 40°, the correlation coefficients between the NIR, GR, VIS, and UV surface albedos and 2-cm soil moisture are becoming larger. And the linear regression coefficients between the NIR, GR, VIS, and UV surface albedos and 2-cm soil moisture are becoming smaller. Shorter wavelengths correspond to stronger relationships between the surface albedo and soil moisture. At longer wavelengths, the decrease in the surface albedo due to the increase in soil moisture is sharper.

Effects of Dynamic Range and Sampling Rate of an Infrared Thermometer to the Accuracy of the Cloud Detection

Cloud detection using downwelling radiation measured by infrared thermometer (IRT) has been utilized for many applications. The current study investigates the effects of disparate IRT specifications, including the dynamic range and sampling rates on the performance of cloud detection, which utilizes the spectral and temporal characteristics of cloudy radiation. To analyze the effects, the detection algorithm that was prepared with and applied to the IRT data with different specifications is compared with reference data, a ceilometer, and micro-pulse lidar (MPL). The comparison results show that the low-altitude clouds are detected with a sufficient accuracy: better than 97% probability of detection (POD). This is due to the much warmer brightness temperature (Tb) of the low clouds compared with the clear sky in the atmospheric window region where the IRT measurement was made. Conversely, the high-altitude cold clouds are hard to detect with the spectral test due to the much-reduced Tb contrast between cloudy and clear sky. Thus, the algorithm performance is largely dependent on the performance of the temporal test. Since the lower measurement noise provides a better estimation of the temporal variability of clear sky Tb with less estimation uncertainty, the IRT data having a better noise performance shows a better POD value by as much as 52.2% compared with the MPL result. However, the improvement is realized only when the dynamic range of IRT covers sufficiently cold Tb, such as −100 °C.

Spectral and Spatial Features of Radiation Emitted by a Cholesteric Liquid-Crystal Laser

Spectral and spatial characteristics of radiation emitted by a laser operating on the Bragg structure arising in cholesteric liquid crystals (CLCs) have been studied, as well as their variations with a change of the planar CLC orientation. A defect in the helical structure of the CLC formed by a ternary mixture of cholesterol viscous esters is revealed at the mutually orthogonal orientations of the CLC director at the substrates. This defect manifests itself as a local dip in the selective reflection band, which agrees with the behavior of the defect mode in the photonic crystal. Such a defect in the helical structure stimulates the selection of longitudinal modes with the indices N = ±1, so that the single-mode lasing regime is realized. A spatial ring structure in the laser radiation is found to arise, when higher longitudinal modes are generated.

Progress and plans of X-ray temporal and spatial diagnosis technology of Shenguang facilities

In the field of indirect-drive inertial confinement fusion, temporal and spatial diagnosis of X-ray is very important to the imploded process researches and the simulate procedure verification. According to the temporal, spatial and spectral characteristics of X-ray radiation, many X-ray imaging diagnosis devices were successfully developed. Along with the development of ICF research, especially the Shenguang III facility establishment, our X-ray imaging diagnosis capability has been increasingly powerful. Some of the novel diagnosis equipment even have more excellent characteristics than that kind of diagnosis equipment abroad.

The influence of protective netting on tree physiology and fruit quality of apple: A review

Abstract The use of protective netting (also called shade nets or anti-hail nets) is being increasingly adopted in apple (Malus × domestica) production. Protective netting is mainly used to prevent fruit sunburn and protect trees against hail damage. Netting can also be used for protection against damage from birds, fruit bats, insects, wind and sand storms. In recent times, protective nets have been modified into photoselective nets by incorporating chromatic elements into the netting material. These change the spectral characteristics of the solar radiation reaching the tree canopy below the net and can affect physiological pathways that respond to the altered light spectra. Protective netting primarily modifies light quantity and quality underneath by reducing light intensity by an approximately pre-determined percentage. Protective netting has also been reported to reduce wind speed and soil temperature with minimal impact on canopy temperature and relative humidity. Quantifying the influence of protective netting on tree gas exchange has been difficult due to variations in the environmental conditions at the time of measurement. Reductions in light intensity due to protective netting result in increased leaf area, shoot length, and total shoot fresh weight that increases as the net shading percentage increases. Fruit set, return bloom, and flower induction are all affected by protective netting. Ultimately, fruit quality is the critical factor determining whether protective netting is suitable for apple production. The reported results on the effect of protective netting on fruit quality have not been conclusive. It has been suggested that changes in fruit quality under protective netting are often more influenced by the environmental conditions in that specific growing season than the netting itself. For example, typical shade responses under netting can be exacerbated when the natural overall light intensity is reduced on cloudy days. In conclusion, protective netting provides an alternative to traditional approaches to protecting apple from sunburn, mechanical injury from hail and wind, and abiotic stress that limits tree productivity. However, the inconsistent reported results suggest a targeted approach is needed to identify specific physiological responses of apple under protective netting, and more specifically, photoselective netting as a strategy to protect apple orchards from adverse environmental conditions.

Soot and spectral radiation modeling for high-pressure turbulent spray flames

A transported probability density function (PDF) method and a photon Monte Carlo/line-by-line (PMC/LBL) spectral model are exercised to generate physical insight into soot processes and spectral radiation characteristics in transient high-pressure turbulent n-dodecane spray flames, under conditions that are relevant for compression-ignition piston engines. PDF model results are compared with experimental measurements and with results from a locally well-stirred reactor (WSR) model that neglects unresolved turbulent fluctuations in composition and temperature. Computed total soot mass and soot spatial distributions are highly sensitive to the modeling of unresolved turbulent fluctuations. To achieve reasonable agreement between model and experiment and to capture the highly intermittent nature of soot in the turbulent flame, it is necessary to accurately represent mixing and the low diffusivity of soot particles. This is accomplished in the PDF framework using a mixing model that enforces locality in the gas-phase composition space, while not mixing the transported soot variables. The results suggest that mixing is at least as important as kinetics in controlling soot formation and evolution in high-pressure turbulent flames. Regarding radiation, radiant fractions and global influences of radiation in these flames are relatively small. Nevertheless, an examination of spectral radiative heat transfer provides valuable insight into the nature and modeling of radiation in high-pressure turbulent combustion systems. There are complex spectral interactions that are revealed using PMC/LBL. CO2 dominates the total radiative emission and reabsorption, but most of the emitted CO2 radiation is reabsorbed before reaching the walls. On the other hand, most of the emitted soot radiation reaches the walls, but soot radiation is a small contribution overall; H2O dominates the radiation that reaches the walls. Global turbulence–radiation interactions (TRI) effects are small, but radiative emission from soot increases by approximately a factor two when TRI are considered. Radiative transfer contributes both to energy redistribution in the vessel and to wall heat losses. The results suggest that a simple model that considers soot radiation and the principal CO2 and H2O spectral bands might be sufficient to capture the key influences of radiation in engine CFD. It is expected that these findings will contribute to the development of truly predictive CFD models for engines and other high-pressure turbulent combustion systems.

Quantum Nature of Distortion and Delay of Satellite Signals II

A detailed analysis of the influence of Rydberg states to the behavior of GPS satellite signals in the D and E atmospheric layers has been carried out. It is demonstrated that these states are the main reason for the GPS signal distortion. It is shown that the behavior of satellite signals is associated with the spectral characteristics of the UHF radiation of the Rydberg states depending on the geomagnetic conditions of ionosphere. The foundations of the quantum theory of distortion and delay of GPS satellite signal propagation through D and E atmospheric layers are analyzed and expounded. The problem reduces to the resonant scattering of photons, moving in the electromagnetic field of the signal, to the Rydberg complexes populated in a two-temperature non-equilibrium plasma. The processes of creation of additional photons because of stimulated emission and resonance scattering of photons are considered. In the present work, the quantum theory of the propagation of a satellite signal in the Earth’s upper atmosphere, firstly earlier proposed by the same authors, is described in detail. The general problems of the theory and possible theoretical and applied consequences are discussed. It is explained that two main processes occurring here, are directly related to the resonant quantum properties of the propagation medium. The first process leads to a direct increase in the power of the received signal, and second—to a shift in the signal carrier frequency and the time delay of its propagation. The main reasons of the processes are scattering of the Rydberg electron by the ion core and presence of the neutral medium molecule in the intermediate autoionization states of the composite system populated by the strong non-adiabatic coupling of electron and nuclear motions. The main purposes of our investigation are the physical justification of the formation of parameters and using the quantum dynamics of the electron behavior in the intermediate state of the Rydberg complex A**M and the estimation of the quantities of and in the elementary act of elastic (Rayleigh) photon scattering.

轻气炮加载下蓝宝石的辐射光谱特性

轻气炮加载下蓝宝石的辐射光谱特性

Spatiotemporal and spectral characteristics of X-ray radiation emitted by the Z-pinch during the current implosion of quasispherical multiwire arrays

For the first time, a quasi-spherical current implosion has been experimentally realized on a multimegaampere facility with the peak current of up to 4 MA and a soft X-ray source has been created with high radiation power density on its surface of up to 3 TW/cm2. An increase in the energy density at the centre of the source of soft X-ray radiation (SXR) was experimentally observed upon compression of quasi-spherical arrays with the linear-mass profiling. In this case, the average power density on the surface of the SXR source is three times higher than for implosions of cylindrical arrays of the same mass and close values of the discharge current. Obtained experimental data are compared with the results of modelling the current implosion of multi-wire arrays performed with the help of a three-dimensional radiation-magneto-hydrodynamic code.

Investigation of Spectral Characteristics of Pulsed Xenon Lamps for Combined Photochemical Degradation of Organometallic Compounds in Liquid Radioactive Waste

The paper considers the composition of liquid radioactive wastes from the nuclear plants. Using traditional ways to extract organometallic compounds formed, when using the deactivation solutions to clean the surfaces of nuclear plant rooms, are complicated. The paper studies the edge-cutting methods of solving this problem. Its proposal is to use a combined ultraviolet treatment for organometallic compounds degradation based on ethylenediaminetetraacetic acid (EDTA) via pulsed xenon lamps. A potential use of the tubular and spherical geometry lamps is examined and advantages, disadvantages and features of these lamps are described. Instead of the pure EDTA the experiments used its disodium salt ( Na 2 -EDTA). The hydrogen peroxide was used as an extra oxidizer. Absorption spectrums of solutions with various Na 2 -EDTA - hydrogen peroxide ratio were measured. It is found that the absorbance curve maximum is in the shortwave spectrum region (λ < 210 nm). The use of amalgam lamps of monochromatic radiation at wavelength λ = 254 nm will result only in formation of hydroxyl radicals but direct destruction processes of EDTA molecules due to radiation will be rare, and this decreases efficiency of their use. The spectral radiation characteristics of various continuum spectrum pulsed xenon lamps was measured. The experimental data expressed in relative units were compared with the emission spectrum of an absolutely black body. The paper shows that in spherical lamps high brightness temperature can be reached. Thus, in spherical lamps it is possible to obtain a spectrum, which is in maximum correlation with the absorption spectrum of the solutions under study, thereby making them a prospective radiation source for photo-degradation of EDTA compounds. For drawing a final conclusion it is necessary to conduct researches in order to compare Na 2 -EDTA degradation via tubular and spherical xenon lamps.

Luminescence of tungsten centers in zinc selenide

Luminescence spectra of W centers in ZnSe are studied. Radiative d–d transitions are identified by the Tanabe–Sugano diagram of the crystal field theory. It is found that the type of electronic transitions changes with a significant change in spectral characteristics of impurity radiation during the transition fromthe 3d- to 5d-electronic systemof impurity centers in the crystals under study.

Radiative d–d transitions at tungsten centers in II–VI semiconductors

The luminescence spectra of W impurity centers in II–VI semiconductors, specifically, ZnSe, CdS, and CdSe, are studied. It is found that, if the electron system of 5d (W) centers is considered instead of the electron system of 3d (Cr) centers, the spectral characteristics of the impurity radiation are substantially changed. The electron transitions are identified in accordance with Tanabe–Sugano diagrams of crystal field theory. With consideration for the specific features of the spectra, it is established that, in the crystals under study, radiative transitions at 5d W centers occur between levels with different spins in the region of a weak crystal field.

Ground-based optical detection of low-dynamic vehicles in near-space

Ground-based optical detection of low-dynamic vehicles in near-space is analyzed to detect, identify, and track high-altitude balloons and airships. The spectral irradiance of a representative vehicle on the entrance pupil plane of ground-based optoelectronic equipment was obtained by analyzing the influence of its geometry, surface material characteristics, infrared self-radiation, and the reflected background radiation. Spectral radiation characteristics of the target in both clear weather and complex meteorological weather were simulated. The simulation results show the potential feasibility of using visible–near-infrared (VNIR) equipment to detect objects in clear weather and long-wave infrared (LWIR) equipment to detect objects in complex meteorological weather. A ground-based VNIR and LWIR optoelectronic experimental setup is built to detect low-dynamic vehicles in different weather. A series of experiments in different weather are carried out. The experiment results validate the correctness of the simulation results.

Impact of soil moisture and winter wheat height from the Loess Plateau in Northwest China on surface spectral albedo

The understanding of surface spectral radiation and reflected radiation characteristics of different surfaces in different climate zones aids in the interpretation of regional surface energy transfers and the development of land surface models. This study analysed surface spectral radiation variations and corresponding surface albedo characteristics at different wavelengths as well as the relationship between 5-cm soil moisture and surface albedo on typical sunny days during the winter wheat growth period. The analysis was conducted using observational Loess Plateau winter wheat data from 2015. The results show that the ratio of atmospheric downward radiation to global radiation on typical sunny days is highest for near-infrared wavelengths, followed by visible wavelengths and ultraviolet wavelengths, with values of 57.3, 38.7 and 4.0%, respectively. The ratio of reflected spectral radiation to global radiation varies based on land surface type. The visible radiation reflected by vegetated surfaces is far less than that reflected by bare ground, with surface albedos of 0.045 and 0.27, respectively. Thus, vegetated surfaces absorb more visible radiation than bare ground. The atmospheric downward spectral radiation to global radiation diurnal variation ratios vary for near-infrared wavelengths versus visible and ultraviolet wavelengths on typical sunny days. The near-infrared wavelengths ratio is higher in the morning and evening and lower at noon. The visible and ultraviolet wavelengths ratios are lower in the morning and evening and higher at noon. Visible and ultraviolet wavelength surface albedo is affected by 5-cm soil moisture, demonstrating a significant negative correlation. Excluding near-infrared wavelengths, correlations between surface albedo and 5-cm soil moisture pass the 99% confidence test at each wavelength. The correlation with 5-cm soil moisture is more significant at shorter wavelengths. However, this study obtained surface spectral radiation characteristics that were affected by land surface vegetation coverage as well as by soil physical properties.

Is conversion efficiency still relevant to qualify advanced multi-junction solar cells?

For better conversion of sunlight into electricity, advanced architectures of multi-junction (MJ) solar cells include increasing numbers of subcells. The Achilles’ heel of these cells lies in their increased sensitivity to the spectral distribution of sunlight, which is likely to significantly alter their performance during real working operation. This study investigates the capacity of MJ solar cells comprising up to 10 subcells to accommodate a wide range of spectral characteristics of the incident radiation. A systematic study is performed, aimed at a realistic estimation of the energy output of MJ-based concentrating photovoltaic systems at characteristic locations selected to represent a large range of climatic conditions. We show that optimal MJ architectures could have between 4 and 7 subcells. Beyond seven subcells, the slight gains in peak efficiency are likely outweighed by detrimental increases in dependence on local conditions and in annual yield variability. The relevance of considering either conversion efficiency or modeled energy output as the most appropriate indicator of the cell performance, when considering advanced architectures of MJ solar cells, is also discussed.

Optical Characteristics of a Gas Discharge Plasma Based on a Mixture of Mercury Diiodide Vapor, Nitrogen, and Helium

The results of studies of spectral, temporal, and energy characteristics of radiation in a gas discharge plasma based on a mixture of mercury diiodide vapor with helium and nitrogen in the spectral range of 350–800 nm are presented. Plasma was produced by a barrier discharge in a device with a cylindrical aperture. The electrodes 0.2 m in length were placed at a distance of 0.015 m. The amplitude of the pump pulses, their duration, and frequency were equal to 20–30 kV, 150 ns, and 1–20 kHz, respectively. Radiation of mercury monoiodide exciplex molecules was revealed in the visible spectra region. Dependences of the plasma optical characteristics on the partial pressures of the mixture components were established.

Can spherical eukaryotic microalgae cells be treated as optically homogeneous?

This study aims to answer the question of whether spherical unicellular photoautotrophic eukaryotic microalgae cells, consisting of various intracellular compartments with their respective optical properties, can be modeled as homogeneous spheres with some effective complex index of refraction. The spectral radiation characteristics in the photosynthetically active region of a spherical heterogeneous microalgae cell, representative of Chlamydomonas reinhardtii and consisting of spherical compartments corresponding to the cell wall, cytoplasm, chloroplast, nucleus, and mitochondria, were estimated using the superposition T-matrix method. The effects of the presence of intracellular lipids and/or starch accumulation caused by stresses, such as nitrogen limitation, were explored. Predictions by the T-matrix method were qualitatively and quantitatively consistent with experimental measurements for various microalgae species. The volume-equivalent homogeneous sphere approximation with volume-averaged effective complex index of refraction gave accurate estimates of the spectral (i) absorption and (ii) scattering cross sections of the heterogeneous cells under both nitrogen-replete and nitrogen-limited conditions. In addition, the effect of a strongly refracting cell wall, representative of Chlorella vulgaris, was investigated. In this case, for the purpose of predicting their integral radiation characteristics, the microalgae should be represented as a coated sphere with a coating corresponding to the cell wall and a homogeneous core with volume-averaged complex index of refraction for the rest of the cell. However, both homogeneous sphere and coated sphere approximations predicted strong resonances in the scattering phase function and spectral backscattering cross section that were not observed in that of the heterogeneous cells.

Comparative spectral characteristics of solar radiation relative to air mass values

The results of the studies of the spectral characteristics of terrestrial solar radiation carried out based on the calculation model for an index dependence of spectral air mass transmission coefficients relative to the standard solar radiation АМ-1.5 are presented for different air mass values. Spectral transmission coefficients for standard air mass АМ-1.5 relative to extraterrestrial solar radiation AM-0 are obtained by comparing the respective spectral intensities from the published literature. During the theoretical calculations, the limiting value of the air mass (for the solar disk near the horizon) is taken to be large by a factor of 36 than for air mass AM-1.

Emission of terahertz waves in the interaction of a laser pulse with clusters

A theory of generation of terahertz radiation in the interaction of a femtosecond laser pulse with a spherical cluster is developed for the case in which the density of free electrons in the cluster plasma exceeds the critical value. The spectral, angular, and energy characteristics of the emitted terahertz radiation are investigated, as well as its spatiotemporal structure. It is shown that the directional pattern of radiation has a quadrupole structure and that the emission spectrum has a broad maximum at a frequency nearly equal to the reciprocal of the laser pulse duration. It is found that the total radiated energy depends strongly on the cluster size. Analysis of the spatiotemporal profile of the terahertz signal shows that it has a femtosecond duration and contains only two oscillation cycles.