Angular Distribution Of Radiation Research Articles

Декомпозиционная оптико-механическая модель светодиодного излучающего элемента

Light-emitting diodes are ahead of traditional light sources in terms of luminous efficacy (luminous flux per unit of electrical power consumption), which arouses an increased interest in the developers of LED lamps in the standard size of incandescent lamps. When designing LED lamps for direct replacement of incandescent lamps, it is necessary to ensure a spherical light distribution in these lighting devices. The design of the lamp with filamentary LED emitting elements is recognized as the best in terms of uniformity of the spatial distribution of light. In this work, a decomposition model of an LED emitting element has been developed, which is created on the basis of the parameters of an optical-mechanical model of LED emitting crystals, and includes the following sequentially performed actions: – construction of a geometric model of the LED emitting element; – determination of the properties of the surface source of the LED emitting element and the angular distribution of radiation of the LED emitting element model as a point emitter; – development of a primary model of an LED crystal with subsequent adjustment of its parameters; – verification of the decomposition model by comparison with the experimentally measured parameters of the LED emitting element. An assessment of the quality of the LED emitting element model as a point emitter was carried out; for this, the averaged measured and modeled LIDCs were superimposed at the same azimuthal angles on top of each other. The discrepancies between the calculated and experimental data do not exceed 10%, which confirms a high accuracy of the LED emitting element model as a point emitter. The resulting file is the properties of the surface source and the value of the luminous flux of the LED emitting element, equal to FW = 254 mW. The model is characterized by increased versatility and can be used for LED emitting elements with an arbitrary configuration of LED crystals and LED lamps based on them.

Modelling a Spectral Index to Detect Dispersed Oil in a Seawater Column Depending on the Viewing Angle: Gulf of Gdańsk Case Study

This paper analyzes the digital modelling of radiance reflectance of the sea surface when the water column is polluted by oil-in-water emulsion. A method tracking the fate of two billion virtual solar photons was applied to obtain the angular distribution of bottom-up radiance for a plane of sunlight striking the sea surface. For the calculations, the inherent optical properties of seawater characteristic for the Gulf of Gdańsk (southern Baltic Sea) were used. The analyses were performed for two types of oils with extremely different optical properties for an oil concentration of 10 ppm and for a roughened sea surface with a wind speed of 2 m/s. The spectral index for oil detection in seawater for different viewing angles was determined based on the results obtained for reflectance at eight wavelengths in the range of 412–676 nm for viewing angle in the range from 80° to 0°, both on the side of incidence of direct sunlight and on the opposite side. The resulting calculated spectral indexes for different wavelength combinations indicated significant dependence on the viewing angle.

Dust particle size, shape and optical depth during the 2018/MY34 martian global dust storm retrieved by MSL Curiosity rover Navigation Cameras

Martian planet-encircling dust storms or global dust storms (GDS), resulting from the combined influence of local and regional storms, are uncommon aperiodic phenomena: with an average frequency of approximately one every 3–4 MY, they produce a substantial rise in the atmospheric dust loading that lasts from weeks to months and have a significant impact on the atmospheric properties, energy budget, and global circulation. During the 2018/MY34 global dust storm, initiated at LS = 185° (30–31 May 2018), an intensive atmospheric science campaign was carried out by the Mars Science Laboratory (MSL) rover to monitor the environmental parameters at Gale Crater. We contribute to previous studies with independent retrievals to constrain the dust opacity and characterise the aerosol particle properties, including: size, shape and single scattering phase function. An iterative radiative transfer retrieval procedure was implemented to determine the aerosol parameters that best fit the angular distribution of sky radiance at forward and backward scattering regions observed by MSL Navigation Cameras (Navcams) during the 2018/MY34 GDS. The MOPSMAP aerosol database and Double Henyey-Greenstein (DHG) analytical single scattering phase functions were used to model the Martian dust aerosol. Outcomes of this study show a steep rise in dust opacity from pre-storm levels of 1.2 up to τ > 9, correlated to particle size variations from 1 to 4 μm. DHG phase functions are characterised with an average asymmetry parameter of g = 0.60 ± 0.11 during the storm, diverging from values of around 0.71 ± 0.06 for the same period in previous MY. Best fitting simulations to backscatter observations for high-opacity periods were generated by a mixture of spheroids following a log-normal distribution of aspect ratios centred on 2.8 ± 0.9, in contrast to values of 1.8 in post-storm sols, thus pointing to more irregular particle shapes at the peak of the dust storm.

On the Spatial Features of the Instantaneous Angular Distribution of Synchrotron Radiation

The instantaneous angular distribution of synchrotron radiation is investigated. The radiation space is divided into two parts. The first part of the space is the interior of a cone with the apex located at the point of a radiating charge, the angular span being $2\alpha_0$ and the central axis oriented along the instantaneous velocity of the charge. The second part of the space is the complement of the first part in the entire space. It is shown that the radiation in the ultrarelativistic limit is entirely contained in the first part of the space, and the radiation in the second part (with a non-zero $\alpha_0$) vanishes.

Nonstationary angular distribution of optical field radiance from an isotropic source in sea water

The spatial-angular and temporal characteristics of the radiance of the light field emitted by a nonstationary point isotropic source in sea water are studied. Using the Monte Carlo method, we calculated the pulse transfer functions and frequency responses of the angular radiance distributions at various distances from the source. Particular integral characteristics of the angular radiance distributions are estimated. It is shown that with an increase in the delay time, measured from the time of arrival of ballistic photons, the angular radiance distribution asymptotically tends to be isotropic. The frequency and phase responses of the alternating radiance component from a source modulated by power at a high frequency are studied. It is shown that with an increase in the modulation frequency, the angular distribution of the alternating radiance component is concentrated close to the direction to the source.

Propagation and Depolarization of a Short Pulse of Light in Sea Water

We present the results of a theoretical study of underwater pulse propagation. The vector radiative transfer equation (VRTE) underlies our calculations of the main characteristics of the scattered light field in the pulse. Under the assumption of highly forward scattering in seawater, three separate equations for the basic modes are derived from the exact VRTE. These three equations are further solved both within the small-angle approximation and numerically. The equation for the intensity is analyzed for a power-law parametrization of the wings of the sea water phase function. The distribution of early arrival photons in the pulse, including the peak intensity, is calculated. Simple relations are also presented for the variance of the angular distribution of radiation, the effective duration of the signal and other parameters of the pulse. For linearly and circularly polarized pulses, the temporal profile of the degree of polarization is calculated for actual data on the scattering matrix elements. The degree of polarization is shown to be described by the self-similar dependence on some combination of the transport scattering coefficient, the temporal delay and the source-receiver distance. Our results are in agreement with experimental and Monte-Carlo simulation data. The conclusions of the paper offer a theoretical groundwork for application to underwater imaging, communication and remote sensing.

Quantitative photothermal lock-in thermography imaging of curved surfaces of cylindrical solids

We extend the applications of photothermal radiometric diagnostics to continuously curved cylindrical surface solids using lock-in thermography (LIT) imaging, in which both the photothermally induced surface temperature and the angularly dependent infrared radiation emitted by the curved surface are not constant. Specifically, a theoretical photothermal model is established based on the Green Function method from which the thermal-wave field distribution at different azimuthal angles on the curved surface is obtained and characteristics of the thermal-wave field with different material and measurement parameters/schemes are discussed. A laser-infrared photothermal lock-in imaging system for solid cylindrical samples is established, and the thermal diffusivity of AISI 304 cylindrical steel samples is measured directly based on the LIT images combined with empirically obtained infrared radiation angular distributions over the curved surfaces. The experimental results are in excellent agreement with the theory, which provides a fast and non-destructive quantitative tool for thermophysical evaluation of curved surface solids.

Radiation of Charge Moving Between Two Planar Periodic Wire Structures

The Smith-Purcell radiation of a charged particle moving in a periodic structure is analysed theoretically. The considered structure consists of two planar diffraction gratings with different periods which are formed by parallel conducting wires. The analytical expression for the spectral-angular distribution of radiation is obtained. It is shown that the angular distribution of radiation can be made narrower by using two gratings instead of one, and radiation intensity can be manipulated by parallel relative shift of gratings. The obtained results are of great importance for the research and development of high power radiation sources based on volume free-electron lasers.

Aerosol characterization using satellite remote sensing of light pollution sources at night

ABSTRACT A demanding challenge in atmospheric research is the night-time characterization of aerosols using passive techniques, that is, by extracting information from scattered light that has not been emitted by the observer. Satellite observations of artificial night-time lights have been used to retrieve some basic integral parameters, like the aerosol optical depth. However, a thorough analysis of the scattering processes allows one to obtain substantially more detailed information on aerosol properties. In this letter, we demonstrate a practicable approach for determining the aerosol particle size number distribution function in the air column, based on the measurement of the angular radiance distribution of the scattered light emitted by night-time lights of cities and towns, recorded from low Earth orbit. The method is self-calibrating and does not require the knowledge of the absolute city emissions. The input radiance data are readily available from several spaceborne platforms, like the VIIRS-DNB radiometer onboard the Suomi-NPP satellite.

Angular distribution of high power radiation from a charge rotating around a dielectric ball

We study the angular distribution of the radiation from a relativistic charged particle uniformly rotating along an equatorial orbit around a dielectric ball. Earlier it was shown that for some values of the problem parameters and in the case of weak absorption in the ball material, the radiation intensity on a given harmonic can be essentially larger than that for the same charge rotating in the vacuum or in a homogeneous transparent medium having the same real part of dielectric permittivity as the ball material. The generation of such high power radiation is a consequence of the constructive superposition of electromagnetic oscillations of Cherenkov radiation induced near the trajectory of the particle and partially locked inside the ball. The angular distribution of the number of the emitted quanta is investigated for such high power radiation. It is shown that the radiation is mainly located in the angular range near the rotation plane determined by the Cherenkov condition for the velocity of the charge projection on the ball surface. The numerical analysis is given for balls made of strontium titanate, melted quartz and teflon in the gigahertz and terahertz frequency ranges.

Quasi-Cherenkov Mechanism of Radiation from Relativistic Electrons Flying near a Multilayer Prism Target

The angular characteristics of millimeter radiation generated by a 6.1-MeV electron beam flying near a multilayer prism target consisting of conducting plates separated by vacuum gaps and near a homogeneous Teflon prism have been studied experimentally. The angular distributions of radiation from both targets have been compared. It has been shown that the angular distribution for the Teflon prism is in good agreement with the classical theory of Cherenkov radiation, whereas the evolution of angular distributions for the multilayer target is inconsistent with known expressions with a fixed effective refractive index. Radiation from the multilayer target (quasi-Cherenkov radiation) should assumingly be described by a tensor refractive index.

Hanle effect in laser-induced fluorescence and Na and Fe resonance scattering lidars.

The nature of the Hanle effect on laser-induced fluorescence (LIF) remains subtle and physically ambiguous. By associating the Hanle effect with the linearly superposed phase-locked excited substates induced by laser-like coherent light, this paper attempts to demystify its underlying physics. The resulting LIF radiation leads to angular distribution of radiation, whose detail depends on the quantum structure of the target atoms. Three simple quantum radiators are used to illustrate the fact that LIF could result in distributions ranging from that of spontaneous emission to that of a classical dipole oscillator. The radiation patterns of six Na ${{\rm D}_2}$D2 and five Fe transitions of interest are presented. The nonunity backward enhancement $q$q-factor of a transition alters its contribution proportionally to the received lidar signal; thus, it results in temperature and wind errors if this factor is ignored in data processing of Na and Fe Doppler lidars as well as of the Fe Boltzmann lidar; these errors are shown to be less than 1 K and 1 m/s.

Photonics: Multipolar Conversion Induced Subwavelength High‐Q Kerker Supermodes with Unidirectional Radiations (Laser Photonics Rev. 13(9)/2019)

It is widely known that Q-factors of resonances are inextricably linked to radiation losses, while their connection to angular radiation distributions is largely overlooked. In article number 1900067, Yuntian Chen, Wei Liu, and Weijin Chen revisit arguably the most fundamental model of two-mode coupling, and establish a subtle connection between these two seemingly unrelated properties, revealing the fundamental mechanism of Q-factor enhancement induced by multipolar conversions from lower to higher orders.

On Change in the Silicon Crystal Structure Implanted with Hydrogen Ions during Annealing Based on Three-Crystal X-Ray Diffractometry Data

In this paper, we present the results of a three-crystal X-ray diffractometry (XRD) study of the state of a disturbed layer formed in silicon crystals by implantation of hydrogen ions with energies of 100 + 200 + 300 keV and a total dose of 2 × 1016 cm–2 during the subsequent heat exposure in the temperature range from 200 to 1100°C. Here, X-ray studies were performed in the three-crystal XRD scheme when the sample under consideration operates as a second stationary crystal with various fixed angular detuning α from the Bragg position while the third (perfect) crystal-analyzer sweeps the angular distribution of radiation diffracted by the second crystal. Based on a comparison of the shape of diffraction and diffuse maxima for the samples under study, a qualitative conclusion about a significant transformation of radiation defects at post-implantation annealing was derived.

Measuring the Transverse Sizes of an Electron Beam by the Angular Distribution of the Coherent Radiation of Electrons in a Crystal

A technique for determining the transverse sizes of a beam on a target from the two-dimensional angular distributions of the radiation for two distances between the emitting crystal and a coordinate detector is proposed. The desired sizes are obtained from the results of fitting, in which the fitted function is the distribution at a shorter distance and the fitting function is the convolution of the angular distribution at a greater distance with a two-dimensional Gaussian distribution with the parameters uniquely related to the beam sizes on the target and crystal-to-detector distance. The limits of applicability of the proposed technique are determined.

Diffracted x-ray transition radiation by a “half-bare” electron

The process of diffracted x-ray transition radiation by a high-energy ``half-bare'' electron in a crystalline target is considered in Bragg geometry. The electron is supposed to appear in the mentioned state, in which the field around it is significantly suppressed comparing to the equilibrium Coulomb one, in the result of preliminary penetration through an upstream amorphous target situated on some distance from the crystal. It is shown that the process of the electron's field regeneration after its exit from the upstream target dramatically modifies both the diffracted transition radiation angular distribution and its total yield making them dependent on the distance between the targets. Analytical expressions for these quantities, as well as their simple approximations, are derived. Almost arbitrary crystal orientation is considered. Special attention is drawn to the case of backward radiation geometry when the emitted radiation has to penetrate through the upstream target on its way to the detector.

Об изменении реальной структуры кристаллов кремния, имплантированных ионами водорода, при их отжиге по данным трехкристальной рентгеновской дифрактометрии

AbstractIn this paper, we present the results of a three-crystal X-ray diffractometry (XRD) study of the state of a disturbed layer formed in silicon crystals by implantation of hydrogen ions with energies of 100 + 200 + 300 keV and a total dose of 2 × 10^16 cm^–2 during the subsequent heat exposure in the temperature range from 200 to 1100°C. Here, X-ray studies were performed in the three-crystal XRD scheme when the sample under consideration operates as a second stationary crystal with various fixed angular detuning α from the Bragg position while the third (perfect) crystal-analyzer sweeps the angular distribution of radiation diffracted by the second crystal. Based on a comparison of the shape of diffraction and diffuse maxima for the samples under study, a qualitative conclusion about a significant transformation of radiation defects at post-implantation annealing was derived.

A GIS-based methodology for assigning experimental measurements of angular distribution of sky radiance and luminance to selected sky sectors

Abstract Mathematical models for the estimation of the angular distribution of diffuse radiance/luminance in the sky describe the anisotropic character of diffuse solar radiation and daylight in the sky vault. In most of these models the radiance/luminance of a sky point is determined by the product of the indicatrix function and the gradation function. When developing and/or calibrating these models, it is typical to consider separately the dispersion effects in the direction of the sun's rays and the gradation from the zenith towards the horizon. To do this, the sky is divided into a number of concentric spherical zones around the sun and a number of concentric spherical zones around the zenith. The intersection between both sets of zones delimits a series of sky elements. Unfortunately, these sky elements do not correspond to the 145 patches of sky vault recommended by the International Commission on Illumination (CIE), which are routinely scanned by the existing commercial sky scanners. The identification of the sky elements, geometrically different from those observed by commercial sky scanners, and the assignation of the radiance/luminance values registered by such sky scanners are not analytically trivial tasks. A GIS-based methodology is presented in this work to undertake these goals.

Single-Shot Carrier-Envelope Phase Determination of Long Superintense Laser Pulses.

The impact of the carrier-envelope phase (CEP) of an intense multicycle laser pulse on the radiation of an electron beam during nonlinear Compton scattering is investigated. We have identified a CEP effect specific to the ultrarelativistic regime. When the electron beam counterpropagates with the laser pulse, pronounced high-energy x-ray double peaks emerge near the backward direction relative to the initial electron motion. This is achieved in the relativistic interaction domain, where both the electron energy is required to be lower than for the electron reflection condition at the laser peak and the stochasticity effects in the photon emission need to be weak. The asymmetry parameter of the double peaks in the angular radiation distribution is shown to serve as a sensitive measure for the CEP of up to 10-cycle long laser pulses and can be applied for the characterization of extremely strong laser pulses in present and near future laser facilities.

Energy measurements by means of transition radiation in novel Linacs

Advanced linear accelerator design may use Optical Transition Radiation (OTR) screens to measure beam spot size; for instance, such screens are foreseen in plasma based accelerators (EuPRAXIA@SPARC_LAB) or Compton machines (Gamma Beam Source@ELI-NP). Optical Transition Radiation angular distribution strongly depends on beam energy. Since OTR screens are typically placed in several positions along the Linac to monitor the beam envelope, one may perform a distributed energy measurement along the machine. Furthermore, a single shot energy measurement can be useful in plasma accelerators to measure shot to shot energy variations after the plasma interaction. Preliminary measurements of OTR angular distribution of about 100 MeV electrons have been performed at the SPARC_LAB facility. In this paper, we discuss the sensitivity of this measurement to beam divergence and others parameters, as well as the resolution required and the needed upgrades of conventional OTR diagnostics, using as an example the data collected at SPARC_LAB.