Angular Distribution Of Radiation Research Articles

Cherenkov radiation from relativistic heavy ions: interpretation in terms of diffraction

We demonstrate here the relationship between the diffraction theory and the theory of optical radiation in the vicinity of the Cherenkov cone from relativistic heavy ions taking account of the slowing-down in a radiator. We draw an analogy with the Huygens-Fresnel principle and demonstrate how the Cornu spiral, known in physical optics, is useful for qualitative and quantitative analysis of the shape and width of the non-trivial angular distributions of radiation.

Measurements of jet cross-section ratios in 13 TeV proton-proton collisions with ATLAS

Measurements of jet cross-section ratios between inclusive bins of jet multiplicity are performed in 140 fb−1 of proton-proton collisions with s=13 TeV center-of-mass energy, recorded with the ATLAS detector at CERN’s Large Hadron Collider. These ratios are constructed from double-differential cross-section measurements that are made in bins of jet multiplicity and other observables that are sensitive the energy scale and angular distribution of radiation due to the strong interaction in the final state. Additionally, the scalar sum of the two leading jets’ transverse momenta is measured triple differentially, in bins of the third jet’s transverse momentum and of jet multiplicity. These measurements are unfolded to account for acceptance and detector-related effects. The measured distributions are used to construct ratios of the inclusive jet-multiplicity bins, which have been shown to be sensitive to the strong coupling αS while being less sensitive than other observables to systematic uncertainties and parton distribution functions. The measured distributions are compared with state-of-the-art QCD calculations, including next-to-next-to-leading-order predictions for two- and three-jet events. These predictions are generally found to model the data well and perform best in bins with a modest requirement on the third jet’s transverse momentum. Significant differences between data and Monte Carlo predictions are observed in events with large rapidity gaps and invariant masses of the leading jet pair. Studies leading to reduced jet energy scale uncertainties significantly improve the precision of this work and are documented herein. © 2024 CERN, for the ATLAS Collaboration 2024 CERN

Revealing the Properties of Electrically Driven Optical Antennas via Conductive Atomic Force Microscope.

Light emission from ultracompact electrically driven optical antennas (EDOAs) has garnered significant attention due to its terahertz modulation bandwidth. Typically, the EDOAs are fixed and nonadjustable once fabricated, thus hindering the attempts to investigate the influence of structural geometry on light emission properties. Here, we propose and demonstrate that the EDOAs can be constructed by carefully manipulating the gold-coated tips of atomic force microscopy operated in conductive mode into contact with the optical antennas covered by insulating film, where the position of the tunnel junction on the antenna surface can be controlled with high accuracy and flexibility. Taking gold nanorod antennas covered by HfO2 film as an example, we found that the highest light generation efficiency is obtained when the tunnel junction is located at the shoulder edge of the nanorod antenna, where the bonding dipolar surface plasmon mode in the junction is spectrally and spatially coupled with the longitudinal radiation mode of the EDOAs. Besides, position variation of the tunnel junction on the nanorod surface also strongly influences the far-field radiation angular distribution and emission spectrum. Numerical simulations are in good agreement with the experimental results. Our findings offer fundamental insights into the influence of structural parameters on the light emission performance of EDOAs, thus leading to better design of EDOAs with high light generation efficiency and powerful functionality.

Optimizing Horticulture Luminescent Solar Concentrators via Enhanced Diffuse Emission Enabled by Micro-Cone Arrays.

Optimizing the photon spectrum for photosynthesis concurrently with improving crop yields presents an efficient and sustainable pathway to alleviate global food shortages. Luminescent solar concentrators (LSCs), consisting of transparent host matrices doped with fluorophores, show excellent promise to achieve the desired spectral tailoring. However, conventional LSCs are predominantly engineered for photon concentration, which results in a limited outcoupling efficiency of converted photons. Here, we introduce a scheme to implement LSCs into horticulture (HLSC) by enhancing light extraction. The symmetry of the device is disrupted by incorporating microcone arrays on the bottom surface to mitigate total internal reflection. Both Monte Carlo ray tracing simulations and experimental results have verified that the greatest enhancements in converted light extraction, relative to planar LSCs, are achieved using microcone arrays (base width 50 μm, aspect ratio 1.2) with extruded and protruded profiles (85.15 and 66.55% improvement, respectively). Angularly resolved transmission measurements show that the HLSC device exhibits a broad angular radiation distribution. This characteristic indicates that the HLSC device emits diffuse light, which is conducive to optimal plant growth.

Mass suppression effect in QCD radiation and hadron angular distribution in jet* *Supported by the National Science Foundation of China (12235008, 12275156, 12275157, 12321005)

The finite mass of the heavy quark suppresses the collimated radiations; this is generally referred to as the dead cone effect. In this paper, we study the distribution of hadron multiplicity over the hadron opening angle with respect to the jet axis for various jet flavors. The corresponding measurement can be the most straightforward and simplest approach to explore the dynamical evolution of the radiations in the corresponding jet, which can expose the mass effect. We also propose a transverse energy-weighted angular distribution, which sheds light on the interplay between perturbative and non-perturbative effects in the radiation. Through Monte-Carlo simulations, our calculations show that the dead cone effect can be clearly observed by finding the ratio between the b and light-quark (inclusive) jets; this is expected to be measured at the LHC in the future.

Variable laser profiles and polarization states in the wave-mixing scheme for the generation of THz radiation in collisional-magnetized clustered-plasma

The four-wave mixing (FWM) mechanism for the generation of Terahertz (THz) radiation in magnetized-collisional clustered-plasma is studied. Clusters can trap the incident laser fields, leading to efficient energy transfer to plasma electrons and the creation of a strong nonlinear current. The size and density of clusters can be tuned to control the emission of THz radiation. The smaller clusters can bring about higher intensity THz radiation, while larger clusters can contribute to the broader THz frequency range. The THz radiation angular distribution patterns in the forward direction have been assessed, and the impact of plasma interaction length, cluster radius, and plasma electrons collision frequency on the generated THz wave patterns has been investigated. The FWM analysis highlights the importance of plasma clusters as well as magnetic fields in the efficient generation of THz emission. The model also takes into consideration how an induced electron current density initiated by DC external magnetic field can boost radiation power without changing the directivity diagram.

A study on angular distribution of THz radiation driven by two-colour laser-induced microplasma

We present an analytical method to study the angular distribution of THz radiation driven by two-colour laser-induced microplasma in nitrogen gas. Directionally dependent temporal waveforms of the radiated THz pulse is calculated. To do so, we have extended the photo-current model to calculate three-dimensional distribution of the photo-induced current from which the far-field THz radiation is computed. We have also studied the effect of optical polarization state and phase difference on the angular distribution of radiation. Our study shows that for two orthogonally-polarized colours, not only THz polarization state, but also the angular distribution of THz radiation is mostly influenced by the second optical harmonic. The possibility of rotating the angular radiation pattern around the axis of the laser propagation is illustrated for circularly-polarized laser drivers by changing the optical phase difference.

Stochastic simulation of a signal on a photodetector matrix of a laser navigation system

Abstract Algorithms for stochastic simulation of the signal arriving at the photodetector matrix of the aircraft navigation system are constructed. During the operation of the aircraft landing navigation system, the laser beam of the navigation system coincides in its direction with the glide path determining safe landing. Two photodetector units placed on board of the aircraft determine the glide path position in the coordinate system of the aircraft, which allows one to adjust the position of the touch point on the runway in poor visibility conditions. In this case, the estimation of the power and angular distributions of radiation recorded by the receiver of the navigation system is a relevant problem. In addition, it is interesting to study the effect of scattering of various multiplicities on the recorded signal. The algorithms developed here are based on direct statistical modelling (estimation over collisions) and local estimates of the Monte Carlo method. The calculations show that the proposed methods allow us to evaluate the efficiency of the laser navigation system in various conditions.

Error analysis of multi-scale aerosol optical properties in shortwave radiative transfer

Atmospheric aerosols can significantly affect atmospheric radiative transfer, especially for shortwave radiation. In this paper, the differences between the bin method and the parameterization method for determining the aerosol optical properties using particle size distribution on the effect of solar shortwave radiation have been discussed according to the developed vector radiative transfer model. The aerosol particle size is divided into multiple regions in the bin method and each region has separate optical properties, while the optical properties of the parameterization method are obtained by integrating the entire size distribution and remain constant. Firstly, the accuracy of the model has been verified by Rayleigh scattering and field distribution simulations, and the validation results show that the average errors of normalized radiation intensity, Stokes components Q and U are 1.36%, 0.79%, and 5.82%, respectively. Subsequently, the angular distribution of radiation, the radiation characteristics of different model parameters, and the field distribution of polarization characteristics under the two methods have been calculated, and the relative errors between the methods have been discussed. The results show that the differences between the two methods are significant, and the angular radiation intensity of the bin method is generally larger than that of the parameterization method, with an average error of about 5%. The transmissivity decreases, and reflectivity increases with the increasing SZA (AOD), respectively, but both decrease with the increasing wavelength. For all model parameters, the transmissivity calculated by the bin method is generally smaller than that of the parameterization method, while the reflectivity is larger, indicating that the forward scattering determined by the bin method is weaker and the lateral (backward) scattering is stronger. Besides, the field distribution results show differences in the scattering phase matrix determined by the two methods. This research contributes to the knowledge of climate assessment and target detection.

Dose calibration of Health Canada's Fixed Point Surveillance system for environmental radiation monitoring in terms of air kerma and H*(10)

The environmental radiation exposure in Canada has been monitored since 2002 by Health Canada's Fixed Point Surveillance network. The network consists of over eighty 7.6 cm × 7.6 cm sodium iodide spectrometers, and routinely reports to the public the environmental gamma radiation level throughout Canada. This paper describes the latest dose calibrations to air kerma and ambient dose equivalent for the future upgraded network. The calibration curves were developed using Monte Carlo techniques and further optimized via experiments in various reference fields. The dose calibration was validated over a wide range of gamma energy, dose measurement range, and angle of incidence under laboratory conditions. In environmental monitoring situations, the angular distribution of radiation exposure was analytically calculated by assuming a semi-infinite plume source, semi-infinite planar source, and infinite volume sources for the respective exposure scenarios of radioactive plume, ground contamination, and soil source. By coupling the resultant radiation angular distribution with detector's angular variation on dose response, the overall accuracy of dose measurement in each of these environmental scenarios was estimated. The accuracy is expected to be within ±3.7% for plume radiation, −5.6% for 137Cs ground contamination, and 0% to −17.1% for soil radioactive sources. The under-estimation for soil sources is mainly caused by absorption of radiation in the electronic system underneath the crystal.

The investigation of low-frequency dilaton generation

The electromagnetic source of dilaton radiation is a first invariant of the electromagnetic field tensor. For electromagnetic waves, this invariant can be nonzero only in the near zone. Pulsars and magnetars are natural sources of this type. We calculated the generation of dilatons by a coherent electromagnetic field of rotating magnetic dipole moments of pulsars and magnetars. It was shown that the radiation of dilaton waves occurs at two frequencies: the rotation frequency omega of the magnetic dipole moment of the neutron star, and twice that frequency. The generation of dilatons at frequency omega is maximal when the angle between the magnetic dipole moment and the axis of its rotation is pi /4. If this angle is pi /2, then dilaton radiation at frequency omega does not occur. The generation of dilatons at frequency 2omega is maximal when the angle between the magnetic dipole and the axis of its rotation is pi /2. The angular distribution of radiation of dilatons having a frequency of omega is maximal along the conic surfaces theta =pi /4 and theta =3pi /4. The angular distribution of radiation of dilatons having a frequency of 2omega is maximal in the plane perpendicular to the axis of rotation (theta =pi /2).

Role of laser pulse profile in terahertz radiation from magnetized and collisional clustered plasma by beating laser beams

THz radiation by beating two femtosecond laser pulses in magnetized and collisional clustered plasma for different laser profiles is investigated. Laser pulses interaction with clustered plasma gives rise to transverse nonlinear current at beating frequencies and is responsible for THz generation. In this mechanism, cluster plasmon resonance significantly enhances the efficiency and the phase matching amplifies that further. Variation of electric field amplitude on directivity of generated waves is examined analytically, as well as numerically for different laser profiles. The numerical findings indicated that laser pulse profile is an important tool to control plasma dynamics and a technique to devise for THz radiation harness for especial applications. The angular distribution of the radiation pattern of THz radiation in forward direction is obtained and the effect of external magnetic field, frequency of plasma, cluster radius and electron collision frequency on generated THz wave patterns have been considered. The study shows that external magnetic field induced more electron current density leading to an increase in radiation power with no change in directivity diagram. Substantial enhancement in magnitude of the angular distribution of THz radiation in clustered plasma compared with un-clustered plasma was noted.

THz generation by two-color laser air plasma coupled to antiresonance hollow-core sapphire waveguides: THz-wave delivery and angular distribution management.

In this paper, hollow-core antiresonance sapphire waveguides were applied to guide the THz radiation emitted by the two-color laser air plasma, as well as to manage the THz source angular distribution. For this aim, three distinct waveguides were developed. Each of them is based on a cylindrical sapphire tube, either suspended in free space or coated by a polymer. The waveguides were first studied numerically, using the finite-difference eigenmode method, and experimentally, using the in-house THz pulsed spectrometer. The observed data uncovered the antiresonance regime of their operation, as well as their ability to guide broadband THz pulses over tens of centimeters with a high optical performance. The waveguides were then used to couple and guide (over the considerable distance) of THz radiation from the in-house two-color laser air plasma emitter, that exploits the mJ-energy-level femtosecond pulses of a Ti-sapphire laser. Small dispersion of a THz pulse and low-to-moderate propagation loss in the developed waveguide were observed, along with a considerable narrowing of the THz radiation angular distribution after passing the waveguide. Our findings revealed that such technologically-reliable hollow-core sapphire waveguides can boost the performance of laser air plasma-based THz emitters and make them more suitable for applications in the vigorously-explored THz sensing and exposure technologies.

Radiation from a charge drifting along a cylindrical channel

Radiation of a charged particle moving in a cylindrical channel with elastic walls is studied. We assume that the particle in the channel is in free motion, periodically colliding with the channel wall. Explicit expressions for the spectrum and angular distribution of radiation are obtained. These results can be used to calculate the spectrum and radiation intensity of charged particles in carbon nanotubes of relatively great diameter. The emission spectrum is essentially a bremsstrahlung one, however, periodic collisions of the particle with the wall lead to coherent amplification of radiation at frequencies that are multiples of the collision frequency. If a beam of particles is channeled, then the multiple spectral lines merge into a continuous spectrum.

Formation of Optical Images with Synchrotron Radiation Flux of Relativistic Electrons in the X-Ray Generator "Nestor"

When setting up physical experiments involving the use of the polarization properties of synchrotron radiation (SR) or a monoenergetic photon beam, detailed calculation of the spectral angular distribution of SR and its polarization components is of interest. Consideration of the electron beam size shows that in real conditions the radiation propagating in the plane of the equilibrium orbit will not be completely polarized, and the shape and dimensions of the angular distribution of radiation will be distorted. The motion of electrons in the uniform magnetic field and SR of the beam of relativistic particles in the storage ring of "NESTOR" are considered. The effect of the size of the electron beam with the energy of E=225 MeV in the 6-dimensional space on the formation of images of the flux of quanta of SR is analyzed. It is shown that the main contribution to the formation of images is made by the two-dimensional distribution of particles along the vertical direction axis and vertical oscillations. A software simulation code has been developed, the use of which made it possible to simulate the process of optical image formations by the flux of SR quanta (Этого предложения нет в русской аннотации). The formation of images of the radiation of electrons with an energy of E=225 MeV with change in the longitudinal distance L to the registration plane is considered. It is determined that at small longitudinal distances the main contribution to the image is made by the vertical distribution of particles in the beam. With an increase in the basic distance L, the contribution of the distribution of particles over vertical oscillations increases, which becomes decisive for large L value. Numerical simulation of image formation has been carried out. For the base distance of 300 cm and beam parameters with the vertical root mean square size of 0.2 mm and a vertical root mean square size of 0.15 mrad, the family of angular distributions is presented in the form of two-dimensional histograms for wavelengths , , , where , is the critical wavelength of SR. The dimensions of the optical window are obtained, the size of which makes it possible to reliably register the entire flux of SR quanta for the indicated registration characteristics.

Vortex and symmetric radiation character of nonlinear Thomson scattering in Laguerre-Gaussian circularly polarized laser pulses.

The radiation character of nonlinear Thomson scattering is investigated in the interaction of Lagueree-Gaussian circularly polarized laser pulses with a single electron in the angular plane. With theoretical analysis and numerical calculation, it is shown that the angular radiation distributions have annular structures with great fourfold or plane symmetry in pulses characterized by comparatively lower laser intensity (a0 < 6), prolonged pulse duration (τ > 50fs)or wide beam waist (b0 > 5μm). In other circumstances, a vortex radiation pattern is found for the first time on the basis of the electron dynamics. Further, by increasing the initial phase of laser pulse, the overall angular radiation has an interesting counter-clockwise rotating trend with a cycle of Δξ0 = 2π. These results would help the understanding of nonlinear Thomson scattering and push forward the research of twisted X/γ-ray generation in optical laboratory.

Methods to measure the radiant flux of light-emitting diodes

To measure the radiant flux of light-emitting diodes, sphere integration, goniophotometric, and pulsed methods have been considered. A convenient method to calculate the radiant flux using the indicatrix of radiant intensity and an integrating sphere design to measure the total radiant flux of light-emitting diodes with a wide angular distribution of radiation have been proposed. Moreover, the calibration of measurement equipment has been considered. The proposed methods and measurement tools help enable the measurement of the radiant flux of light-emitting diodes in the range of 1 mW to tens of watts. The measurement results are compared using different methods. A method to estimate the absolute measurement error is proposed.

Analytical expressions for estimating sky diffuse irradiance and illuminance on tilted planes for the CIE Standard General Skies

This work proposes a set of analytical expressions for the calculation of the relationship between sky diffuse illuminance on a tilted plane and horizontal plane corresponding to the 15 ISO/CIE standard sky types. Given the parallelism in the angular distribution of sky diffuse radiance and luminance, these expressions can also be used to calculate the diffuse sky irradiance on an inclined plane. The proposed analytical expressions are obtained by adjusting the results of a numerical calculation whose methodology is described in detail in the paper. The use of these analytical expressions significantly reduces the calculation time. It is verified that the relative root-mean-square errors obtained with the analytical expressions are small compared with the use of numerical calculation, ranging from 0.03% to 4.09%, and with a tendency to increase with clear skies and high solar zenith angles.

Generation of intense coherent electromagnetic radiation during the interaction of a multi-terawatt laser pulse with a nanowire target* *Reported at the 4th International Conference on Ultrafast Optical Science (Russia, Moscow, FIAN, 28 September – 2 October 2020).

Generation of coherent radiation in the IR and terahertz ranges during the propagation of a multi-terawatt laser pulse along a nanowire target is investigated. In the process of interaction, dense electron bunches are displaced from the target and accelerated in the laser field, generating intense electromagnetic radiation. Three regimes of interaction can be realised depending on the duration and shape of the laser pulse. In the first regime, when the laser pulse is long enough (tens and hundreds of femtoseconds), electrons are only partially forced out of the target. The characteristics of the low-frequency part of the spectrum of the generated radiation are determined in this case by the duration of the laser pulse, as well as by its amplitude and target parameters (geometric dimensions and concentration of electrons). In the second regime, the laser pulse has a large amplitude and a steep rising edge (the amplitude of the first half-wave is of the order of the maximum pulse amplitude); as a result, most of the electrons are displaced from the target already at the initial moment of interaction. In this regime, unipolar and bipolar pulses with a duration of tens of laser field periods can be formed. Changing the target length makes it possible to control the period of field oscillations and their number in the generated radiation. In the intermediate regime of short laser pulses with an insufficiently steep rising edge, oscillations of the formed electron bunches can occur in the macroscopic Coulomb attraction field of the charged target, which gives rise to radiation with a frequency several times lower than that of laser radiation. In this case, the pulses of the generated radiation contain a few cycles of the field with decreasing amplitude and increasing frequency. Using numerical simulation in three regimes of interaction, the characteristics of IR and terahertz radiation are found, in particular, the pulse shapes, ranges of generated frequencies, amplitudes and angular distributions of radiation are determined. It is shown that the amplitude of the generated pulse can reach subrelativistic and relativistic values (the field strength is more than 1 TV m−1 at a frequency ten times lower than the laser radiation frequency), and the energy conversion efficiency can be of the order of one percent.

ПЕРЕТВОРЕННЯ ЗОБРАЖЕНЬ ЕМІСІІ РЕЛЯТИВІСТСЬКИХ ЕЛЕКТРОНІВ І МЕТРОЛОГИЧНІ ХАРАКТЕРИСТИКИ ПОТОКУ ФОТОНІВ В КАНАЛІ ВИВОДУ СИНХРОТРОННОГО ВИПРОМІНЮВАННЯ НАКОПИЧУВАЧА "НЕСТОР" ННЦ ХФТІ

При постановке экспериментов, связанных с использованием поляризационных свойств синхротронного излучения (СИ), представляет интерес детальный расчет спектрального углового распределения СИ и его поляризационных компонент. Учет размеров пучка показывают, что в реальных условиях излучение не будет полностью поляризованным, а форма и размеры углового распределения излучения будут искажены. Рассмотрено движение электронов в однородном магнитном поле и СИ пучка релятивистских частиц в накопителе "НЕСТОР" Национального Научного Центра «Харьковский Физико- Технический Институт» (ННЦ ХФТИ). Проанализировано влияние на формирование изображений потока квантов СИ размеров пучка электронов с энергией Е=225 МэВ. Показано, что в формирование изображений основной вклад вносит двумерное распределение частиц по вертикали и по вертикальным колебаниям. Разработано программное обеспечение, использование которого дало возможность промоделировать процесс формирования оптических изображений потоком квантов СИ. Рассмотрено формирование изображений излучения электронов с энергией Е=225 МэВ при изменении продольного расстояния L до плоскости регистрации. Определено, что на малых продольных расстояниях основной вклад в изображении вносит вертикальное распределение частиц. С увеличением расстояния возрастает вклад распределения частиц по вертикальным колебаниям, который для больших L становится определяющим. Проведено численное моделирование формирования изображений. Приведено семейство угловых распределений плотности потоков σ- и π-компонент поляризации, рассчитанных для одного из каналов вывода СИ накопителя"НЕСТОР". Зависимости оформлены в виде двумерных гистограмм для длины Lmax=300 см, вертикальных среднеквадратичных параметров пучка и разных длин волн излучения, а также для разных дисперсий L σ электронного сгустка. Получены размеры оптического люка, величина которых позволяет гарантированно регистрировать весь поток квантов СИ для указанных характеристик регистрации.