Brightness Of Radiation Research Articles

Effect of Climatological Factors on the Horizontal Accuracy of Photogrammetric Products Obtained with UAV

The use of UAVs (drones) and photogrammetry has gained attention in recent years in the construction industry, allowing information to be obtained from a given area without having direct contact with the area, and thus, being a more efficient alternative in terms of time and costs when compared to a traditional topographic survey. Due to the increase in the use of UAVs for photogrammetry, an investigation is proposed to determine the influence of a non-controllable component in photogrammetric flights: the weather. Factors such as brightness, temperature, wind, KP index, and solar radiation affect the precision and quality of the images to be used in photogrammetry. This research determines which factors are most influential in these results through a varied database obtained over a year. In this way, the moments with the most favorable conditions for a photogrammetric flight in climates such as that of the city of Lima or similar are established. A total of 448 flights carried out over a year were analyzed, collecting climatic data such as air temperature, speed and wind direction, solar radiation, and KP index. The flights, which were carried out with a Mavic 2 Pro UAV, were carried out at 100 m high and with a camera at 90° to obtain detailed information on the works.

Image Dehazing Enhancement Strategy Based on Polarization Detection of Space Targets

In view of the fact that the technology of polarization detection performs better at identifying targets through clouds and fog, the recognition ability of the space target detection system under haze conditions will be improved by applying the technology. However, due to the low ambient brightness and limited target radiation information during space target detection, the polarization information of space target is seriously lost, and the advantages of polarization detection technology in identifying targets through clouds and fog cannot be effectively exerted under the condition of haze detection. In order to solve the above problem, a dehazing enhancement strategy specifically applied to polarization images of space targets is proposed. Firstly, a hybrid multi-channel interpolation method based on regional correlation analysis is proposed to improve the calculation accuracy of polarization information during preprocessing. Secondly, an image processing method based on full polarization information inversion is proposed to obtain the degree of polarization of the image after inversion and the intensity of the image after dehazing. Finally, the image fusion method based on discrete cosine transform is used to obtain the dehazing polarization fusion enhancement image. The effectiveness of the proposed image processing strategy is verified by carrying out simulated and real space target detection experiments. Compared with other methods, by using the proposed image processing strategy, the quality of the polarization images of space targets obtained under the haze condition is significantly improved. Our research results have important practical implications for promoting the wide application of polarization detection technology in the field of space target detection.

Bright unintended electromagnetic radiation from second-generation Starlink satellites

We report on the detection of unintended electromagnetic radiation (UEMR) from the second-generation of Starlink satellites. Observations with the LOFAR radio telescope between 10 to 88 MHz and 110 to 188 MHz show broadband emission covering the frequency ranges from 40 to 70 MHz and 110 to 188 MHz from the v2-Mini and v2-Mini Direct-to-Cell Starlink satellites. The spectral power flux density of this broadband UEMR varies from satellite to satellite, with values ranging from 15 to 1300 Jy, between 56 and 66 MHz, and from 2 to 100 Jy over two distinct 8 MHz frequency ranges centered at 120 and 161 MHz. We compared the detected power flux densities of this UEMR to that emitted by the first generation v1.0 and v1.5 Starlink satellites. When correcting for the observed satellite distances, we find that the second-generation satellites emit UEMR that is up to a factor of 32 stronger compared to the first generation. The calculated electric field strengths of the detected UEMR exceed typical electromagnetic compatibility standards used for commercial electronic devices as well as recommended emission thresholds from the Radiocommunication Sector of the International Telecommunications Union (ITU-R) aimed at protecting the 150.05–153 MHz frequency range allocated to radio astronomy. We characterize the properties of the detected UEMR with the aim of assisting the satellite operator with the identification of the cause of the UEMR.

In-vacuum undulators for the first phase beamlines of Korea-4GSR

Korea-4GSR, a new synchrotron radiation facility currently under construction in Ochang, Chungbuk, South Korea, introduces three types of in-vacuum undulators (IVUs) for its first phase hard X-ray beamlines: IVU20, IVU22, and IVU24. These IVU types share a common 3-m-long framework capable of adjusting the magnetic gap size between 5 and 18 mm, but they differ in the undulator period length (λu). This study characterizes their photon beams in terms of brightness, spectral coverage, source size, angular divergence, coherent fraction, coherent flux, and total and central cone radiation powers, using undulator calculations. The three IVU types are comparable in brightness. IVU20 is the most coherent, although lacking spectral continuity at around 7.5 keV. IVU22 and IVU24 ensure spectral continuity, but their coherent flux is moderately compromised. The performance of the undulators is assessed in comparison to the Pohang Light Source-II (PLS-II) undulator and the U21 undulator at Advanced Photon Source Upgrade (APS-U).

The Effect of the Lorenz Coefficient on the Free Electron Laser

Coherent, high-peak tunable power supplies have been very useful in many applications. In this research, the physical process of a new type of coherent, flexible, and very bright radiation source called the free electron laser (sFEL) is described. The movement of the electron beam in the presence of two fields, optical and wave, leads to the exchange of energy. This energy exchange leads to the formation of groups of electrons that will emit very bright radiation. In principle, the resonance wavelength can be adjusted to any radiation area, and this is possible by changing the wave parameter or the energy of the electron beam. The emitted linear shape has the characteristic shape of short time emission process.

Classifying Microwave Radiometer Observations over the Netherlands into Dry, Shallow, and Nonshallow Precipitation Using a Random Forest Model

Abstract Spaceborne microwave radiometers represent an important component of the Global Precipitation Measurement (GPM) mission due to their frequent sampling of rain systems. Microwave radiometers measure microwave radiation (brightness temperatures Tb), which can be converted into precipitation estimates with appropriate assumptions. However, detecting shallow precipitation systems using spaceborne radiometers is challenging, especially over land, as their weak signals are hard to differentiate from those associated with dry conditions. This study uses a random forest (RF) model to classify microwave radiometer observations as dry, shallow, or nonshallow over the Netherlands—a region with varying surface conditions and frequent occurrence of shallow precipitation. The RF model is trained on five years of data (2016–20) and tested with two independent years (2015 and 2021). The observations are classified using ground-based weather radar echo top heights. Various RF models are assessed, such as using only GPM Microwave Imager (GMI) Tb values as input features or including spatially aligned ERA5 2-m temperature and freezing level reanalysis and/or Dual-Frequency Precipitation Radar (DPR) observations. Independent of the input features, the model performs best in summer and worst in winter. The model classifies observations from high-frequency channels (≥85 GHz) with lower Tb values as nonshallow, higher values as dry, and those in between as shallow. Misclassified footprints exhibit radiometric characteristics corresponding to their assigned class. Case studies reveal dry observations misclassified as shallow are associated with lower Tb values, likely resulting from the presence of ice particles in nonprecipitating clouds. Shallow footprints misclassified as dry are likely related to the absence of ice particles. Significance Statement Published research concerning rainfall retrieval algorithms from microwave radiometers is often focused on the accuracy of these algorithms. While shallow precipitation over land is often characterized as problematic in these studies, little progress has been made with these systems. In particular, precipitation formed by shallow clouds, where shallow refers to the clouds being close to Earth’s surface, is often missed. This study is focused on detecting shallow precipitation and its physical characteristics to further improve its detection from spaceborne sensors. As such, it contributes to understanding which shallow precipitation scenes are challenging to detect from microwave radiometers, suggesting possible ways for algorithm improvement.

Comparative Numerical Analysis of Keyhole Shape and Penetration Depth in Laser Spot Welding of Aluminum with Power Wave Modulation

Keyhole mode laser welding is a valuable technique for welding thick materials in industrial applications. However, its susceptibility to fluctuations and instabilities poses challenges, leading to defects that compromise weld quality. Observing the keyhole during laser welding is challenging due to bright process radiation, and existing observation methods are complex and expensive. This paper alternatively presents a novel numerical modeling approach for laser spot welding of aluminum through a modified mixture theory, a modified level-set (LS) method, and a thermal enthalpy porosity technique. The effects of laser parameters on keyhole penetration depth are investigated, with a focus on laser power, spot radius, frequency, and pulse wave modulation in pulsed wave (PW) versus continuous wave (CW) laser welding. PW laser welding involves the careful modulation of power waves, specifically adjusting the pulse width, pulse number, and pulse shapes. Results indicate a greater than 80 percent increase in the keyhole penetration depth with higher laser power, pulse width, and pulse number, as well as decreased spot radius. Keyhole instabilities are also more pronounced with higher pulse width/numbers and frequencies. Notably, the rectangular pulse shape demonstrates substantially deeper penetration compared to CW welding and other pulse shapes. This study enhances understanding of weld pool dynamics and provides insights into optimizing laser welding parameters to mitigate defects and improve weld quality.

A Sparse Recovery Algorithm for Suppressing Multiple Linear Frequency Modulation Interference in the Synthetic Aperture Radar Image Domain.

In synthetic aperture radar (SAR) signal processing, compared with the raw data of level-0, level-1 SAR images are more readily accessible and available in larger quantities. However, an amount of level-1 images are affected by radio frequency interference (RFI), which typically originates from Linear Frequency Modulation (LFM) signals emitted by ground-based radars. Existing research on interference suppression in level-1 data has primarily focused on two methods: transforming SAR images into simulated echo data for interference suppression, or focusing interference in the frequency domain and applying notching filters to reduce interference energy. However, these methods overlook the effective utilization of the interference parameters or are confined to suppressing only one type of LFM interference at a time. In certain SAR images, multiple types of LFM interference manifest bright radiation artifacts that exhibit varying lengths along the range direction while remaining constant in the azimuth direction. It is necessary to suppress multiple LFM interference on SAR images when original echo data are unavailable. This article proposes a joint sparse recovery algorithm for interference suppression in the SAR image domain. In the SAR image domain, two-dimensional LFM interference typically exhibits differences in parameters such as frequency modulation rate and pulse width in the range direction, while maintaining consistency in the azimuth direction. Based on this observation, this article constructs a series of focusing operators for LFM interference in SAR images. These operators enable the sparse representation of dispersed LFM interference. Subsequently, an optimization model is developed that can effectively suppress multi-LFM interference and reduce image loss with the assistance of a regularization term in the image domain. Simulation experiments conducted in various scenarios validate the superior performance of the proposed method.

The storage ring of the Compton source of the NCPM

In this paper, the magnetic structure of the storage ring of an X-ray source based on the effect of Compton backscattering and designed for use in the electron beam energy range from 35 MeV to 120 MeV is investigated. For this storage ring, the results of calculating the dynamics of the electron beam are presented and the effects of radiation damping, quantum excitation, laser damping and intrabeam scattering are considered. The dynamic aperture and energy acceptance of this ring are discussed. The results of calculating the magnitude of the spectral brightness of X-ray radiation and its change over time are presented.

Tunable energy spectrum betatron x-ray sources in a plasma wakefield

Abstract X-ray sources with tunable energy spectra have a wide range of applications in different scenarios due to their different penetration depths. However, existing x-ray sources face difficulties in terms of energy regulation. In this paper, we present a scheme for tuning the energy spectrum of a betatron x-ray generated from a relativistic electron bunch oscillating in a plasma wakefield. The center energy of the x-ray source can be tuned from several keV to several hundred keV by changing the plasma density, thereby extending the control range by an order of magnitude. At different central energies, the brightness of the betatron radiation is in the range of 3.7 × 1022 to 5.5 × 1022 photons/(0.1%BW⋅s⋅mm2⋅mrad2) and the photon divergence angle is about 2 mrad. This high-brightness, energy-controlled betatron source could pave the way to a wide range of applications requiring photons of specific energy, such as phase-contrast imaging in medicine, non-destructive testing and material analysis in industry, and imaging in nuclear physics.

Accuracy assessment of ground-based microwave radiometer in the Mount Qomolangma region

Mount Qomolangma, known as the “Roof of the World,” holds significant importance in exploring the vertical characteristics of the atmosphere, providing insights into high-altitude atmospheric features, and improving numerical models for forecasting downstream regions. Ground-based microwave radiometers (GWR) enable continuous profiling of atmospheric conditions in the troposphere, complementing radiosonde and satellite observations. This study explores the performance of the MWP967KV GWR installed at Qomolangma Base Camp by comparison with concurrent radiosonde measurements. The assessment covers GWR's atmospheric radiative brightness temperatures (Tb) detection capability, accuracy of atmospheric parameter retrievals, and uncertainties in atmospheric parameters under different weather conditions. Using MonoRTM to calculate simulated Tb from radiosonde, the results indicate a high precision of GWR's Tb observations, showing a strong correlation (R ≈ 0.99) and a deviation of merely 2.4 K compared to simulated Tb. Moreover, GWR exhibits high reliability in temperature (R ≈ 0.98) and water vapor density (ρv) (R ≈ 0.91) observations, while the accuracy of relative humidity (RH) measurements requires improvement (R ≈ 0.55). The GWR observations are affected by clouds, precipitation, and surrounding Qomolangma mountain ridges, leading to significant uncertainties in atmospheric parameter retrievals between 2000 m to 6000 m above ground level. Additionally, GWR's sensitivity to temperature variations is limited, resulting in missed detections of temperature inversion. Despite these limitations, this study offers crucial insights into meteorological observations at high altitudes using GWR. These findings hold substantial implications for meteorological research and mountaineering activities in high-altitude regions.

Experimental investigation of the characteristics of the plasma flow generated in quasi-stationary plasma accelerator using optical methods

The spatial and temporal dependencies of the characteristics of the hydrogen plasma flow generated in quasi-stationary plasma accelerator were investigated. The spatiotemporal structure of discharge radiation in the interelectrode gap was studied. The range of changes in the length of the plasma glowing region in the interelectrode gap during the discharge pulse was determined. The region with bright plasma radiation located in the output face of the accelerator electrode system was observed. The presence of impurities and increased electron concentration values were observed in this region. Fluctuations in the radiation intensity of the plasma flow were detected along the entire length of its propagation. The spatial and temporal characteristics of these fluctuations were determined. The electron concentration values near the output face of the electrode system were obtained by measuring the Stark broadening of the Hβ line. For the first time, the time dependence of the electron concentration of free plasma flow was obtained using two methods simultaneously. The measurements were conducted at a distance, which significantly exceeds the characteristic size of the electrode system and where the influence of interelectrode processes of plasma flow generation is reduced. The first is based on measuring the Stark broadening of Hβ. As a second method, heterodyne interferometry was used.

Characterization of bright betatron radiation generated by direct laser acceleration of electrons in plasma of near critical density

Directed x-rays produced in the interaction of sub-picosecond laser pulses of moderate relativistic intensity with plasma of near-critical density are investigated. Synchrotron-like (betatron) radiation occurs in the process of direct laser acceleration (DLA) of electrons in a relativistic laser channel when the electrons undergo transverse betatron oscillations in self-generated quasi-static electric and magnetic fields. In an experiment at the PHELIX laser system, high-current directed beams of DLA electrons with a mean energy ten times higher than the ponderomotive potential and maximum energy up to 100 MeV were measured at 1019 W/cm2 laser intensity. The spectrum of directed x-rays in the range of 5–60 keV was evaluated using two sets of Ross filters placed at 0° and 10° to the laser pulse propagation axis. The differential x-ray absorption method allowed for absolute measurements of the angular-dependent photon fluence. We report 1013 photons/sr with energies >5 keV measured at 0° to the laser axis and a brilliance of 1021 photons s−1 mm−2 mrad−2 (0.1%BW)−1. The angular distribution of the emission has an FWHM of 14°–16°. Thanks to the ultra-high photon fluence, point-like radiation source, and ultra-short emission time, DLA-based keV backlighters are promising for various applications in high-energy-density research with kilojoule petawatt-class laser facilities.

One in-situ extraction algorithm for monitoring bunch-by-bunch profile in the storage ring

As the brightness of synchrotron radiation (SR) light sources improves, the operation stability of light sources is weakened. To explore various beam instability related issues in light sources, one transverse beam diagnostics system for bunch-by-bunch (BbB) profile measurement has been established at Hefei Light Source-II (HLS-II). In this paper, one in-situ extraction algorithm in the data processing backend of the system is developed for BbB profiles, so as to provide important beam information of the machine operation in time.

Observation of transition from superfluorescence to polariton condensation in CsPbBr3 quantum dots film

The superfluorescence effect has received extensive attention due to the many-body physics of quantum correlation in dipole gas and the optical applications of ultrafast bright radiation field based on the cooperative quantum state. Here, we demonstrate not only to observe the superfluorescence effect but also to control the cooperative state of the excitons ensemble by externally applying a regulatory dimension of coupling light fields. A new quasi-particle called cooperative exciton-polariton is revealed in a light-matter hybrid structure of a perovskite quantum dot thin film spin-coated on a Distributed Bragg Reflector. Above the nonlinear threshold, polaritonic condensation occurs at a nonzero momentum state on the lower polariton branch owning to the vital role of the synchronized excitons. The phase transition from superfluorescence to polariton condensation exhibits typical signatures of a decrease of the linewidth, an increase of the macroscopic coherence as well as an accelerated radiation decay rate. These findings are promising for opening new potential applications for super-brightness and unconventional coherent light sources and could enable the exploitation of cooperative effects for quantum optics.

Enhancing conversion efficiency of MgO:PPLN and Rb:PPKTP crystal-based subnanosecond optical parametric generators by utilizing a supercontinuum seed

This paper presents an approach to enhance the conversion efficiency of subnanosecond pulse duration microlaser-pumped optical parametric generators (OPGs) tunable from near- to mid-infrared. The method involves generating a supercontinuum (SC) in the photonic crystal fiber (PCF) and using it to seed the subnanosecond OPG based on the fan-out grating design MgO:PPLN crystal. Since the SC spectrum covered the entire signal wave tuning range (1414–2128 nm), seeding and conversion efficiency improvement of 6%–11% was achieved for all OPG signal wavelengths, and the generation threshold was reduced up to 3 times. Such a method allows for improved energy stability, significantly increases the brightness of the OPG output radiation, and is pivotal in mitigating the risk of MgO:PPLN optical damage. The study also extended the method to successfully seed 532 nm pumped Rb-doped PPKTP crystal-based OPG with the same SC, demonstrating broad applicability and performance improvement across different parametric devices.

Enhanced harmonic generation for high-repetition-rate soft x-ray free-electron laser

Externally seeded free-electron lasers are promising for generating intense, stable, and fully coherent soft X-ray pulses. An earlier study demonstrates that high brightness and coherent soft X-ray radiation can be produced based on coherent harmonic generation and superradiant principles, termed high-brightness high-gain harmonic generation (HB-HGHG). However, the seed laser at the ultraviolet region cannot induce sufficient energy modulation at high repetition rates due to state-of-the-art laser system limitations. A recently suggested self-modulation scheme shows that the peak power requirement of a seed laser can be reduced by around one order of magnitude in an HGHG setup. In this paper, we present start-to-end simulation results to estimate the feasibility of the self-modulation-enhanced HB-HGHG scheme.

AGILE Gamma-Ray Detection of the Exceptional GRB 221009A

Gamma-ray emission in the MeV–GeV range from explosive cosmic events is of invaluable relevance to understanding physical processes related to the formation of neutron stars and black holes. Here we report on the detection by the AGILE satellite in the MeV–GeV energy range of the remarkable long-duration gamma-ray burst GRB 221009A. The AGILE onboard detectors have good exposure to GRB 221009A during its initial crucial phases. Hard X-ray/MeV emission in the prompt phase lasted hundreds of seconds, with the brightest radiation being emitted between 200 and 300 s after the initial trigger. Very intense GeV gamma-ray emission is detected by AGILE in the prompt and early afterglow phase up to 10,000 s. Time-resolved spectral analysis shows time-variable MeV-peaked emission simultaneous with intense power-law GeV radiation that persists in the afterglow phase. The coexistence during the prompt phase of very intense MeV emission together with highly nonthermal and hardening GeV radiation is a remarkable feature of GRB 221009A. During the prompt phase, the event shows spectrally different MeV and GeV emissions that are most likely generated by physical mechanisms occurring in different locations. AGILE observations provide crucial flux and spectral gamma-ray information regarding the early phases of GRB 221009A during which emission in the TeV range was reported.

Atomic data and expansion opacity calculations in two representative 4d transition elements, niobium and silver, of interest for kilonovae studies

Aims. Neutron star (NS) mergers are thought to be a source of heavy trans-iron element production. The latter can be detected in the spectra of the ejected materials, from which bright electromagnetic radiation is emitted. This latter is due to the radioactive decay of the produced heavy r-process nuclei and is known as kilonova. Because of their complex atomic structures – characterized by configurations involving unfilled nd or nf subshells – the heavy elements of the kilonova ejecta often give rise to numerous absorption lines generating significant opacities. The determination of the latter, which are of paramount importance for the analysis of kilonova light curves, requires knowledge of the radiative parameters of the spectral lines belonging to the ions expected to be present in the kilonova ejecta. The aim of the present work is to provide new atomic opacity data for two representative 4d elements, niobium (Nb) and silver (Ag), in their first four charge states, namely for Nb I–IV and Ag I–IV. Methods. Large-scale calculations based on the pseudo-relativistic Hartree-Fock (HFR) method were performed to obtain the atomic structure and radiative parameters while the expansion formalism was used to estimate the opacities. Results. Wavelengths and oscillator strengths were computed for several million spectral lines in Nb I–IV and Ag I–IV ions. The reliability of these parameters was estimated by comparison with the few previously published experimental and theoretical results. The newly obtained atomic data were then used to calculate expansion opacities for typical kilonova conditions expected one day after NS merger, a density of ρ = 10−13 g cm−3, and temperatures ranging from T = 5000 K to T =15 000 K.

Ozone spectroscopy in the terahertz range from first high-resolution Synchrotron SOLEIL experiments combined with far-infrared measurements and ab initio intensity calculations

Ozone is one of the important molecules in terms of the impact on the atmospheric chemistry, climate changes, bio- and eco-systems and human health. It has a strong absorption in the microwave, terahertz and far-infrared spectral ranges where a large part of the Earth’s outgoing longwave radiation to space is located. In this work, the observations, and analyses of the ozone high-resolution spectra in the THz range recorded using the Synchrotron light source of the SOLEIL CNRS equipment are reported for the first time. Thanks to the exceptional brightness of the Synchrotron radiation and to the signal/noise ratio, it was possible to observe many more ozone transitions of the cold rotational band and the hot ν2-ν2 band in the range 0.9–6 THz compared to the previous works. In addition, we have carried out new measurements and assignments for the ν2 band. The simultaneous fit of the rotational band GS-GS, the hot band ν2-ν2 and the FIR ν2 band yielded an overall weighted standard deviation of 0.68 for 13,466 line positions within the experimental accuracy. This includes all previously available MW (with the best uncertainty 0.1 – 10 kHz), FIR data and the original SOLEIL measurements that provided experimental accuracy of 0.00005 – 0.0001 cm−1 for the best lines. Significant deviations in new experimental spectra compared to available spectroscopic databases were evidenced, particularly for the line positions and energy levels at high J, Ka rotational quantum numbers that are the most pronounced in the 4.5 – 6 THz range. Accurate ab initio calculations of line intensities combined with empirically fitted line positions were used to create new linelists that permit theoretical modelling of the transmittance in a good agreement with the Synchrotron spectra in the entire range of observations for various pressures and optical paths. The region near 100 cm−1 and above appears to be more sensitive to the temperature conditions that should be considered in atmospheric observation for the currently operational and future ground based and space missions.