Radial Intensity Distribution Research Articles

Effect of Ce<sup>3+</sup> Concentration and YAG Crystal Particles Size on Photoluminescence

Purpose of research. Determine the effect on the photoluminescence of phosphors from yttrium-aluminum garnet activated by cerium ions Ce3+, the size of its particles and the concentration of cerium ions in them.Methods. Structural electron and confocal microscopic, fluorescent, microspectral studies using a laser lex = 473 nm as an excitation source, energy dispersive, X-ray diffraction studies, as well as goniophotometric measurements on the radial distribution of light intensity excited by the LED matrix were carried out.Results. A detailed granulometric analysis of the particle sizes of phosphors was carried out for two samples from different manufacturers, cumulative distributions M(d) were constructed and their quantiles were established. Based on the results of measuring photoluminescence from individual particles in the compositions of phosphors based on YAG:Ce3+, a Stokes shift was detected in these samples: short-wavelength – for particles with sizes less than 10 μm and with low concentration and long-wavelength – with sizes greater than 10 μm with an increased concentration of over ~0.2% . The obtained microspectral size-emission dependences lem(d) and energy Imax(d) were consistent with the description based on the proposed physical mechanism of their formation by the 5d → 2F5/2 and 5d → 2F7/2 transitions.Conclusion. A short-wavelength shift of photoluminescence intensity maxima for particles smaller than 10 μm was discovered, due to a significant increase in the influence of surface stresses due to a reduction in the number of atoms. For larger particle sizes, the characteristic photoluminescence intensity maxima cease to depend on the wavelength. The radial distribution of luminous intensity determined by the goniophotometric method made it possible to calculate the value of the luminous flux equal to 1350 lm and 1140 lm, respectively, for LED matrices containing 8 LEDs with the studied phosphors.

Observation of the dynamic evolution process of vacuum arc microscopic particles based on the emission spectrum principle

The distribution of microscopic particles directly affects the recovery of the post arc insulating medium and determines whether the fault current can be interrupted. Based on the principle of vacuum arc emission spectrum, a high-speed spectrum observation platform was built to study the distribution of microscopic particles during the arc burning, and the axial and radial spectral line intensity and density distributions of atoms and ions under different current amplitudes were obtained. The results show that the CuI spectral line intensity has two peaks near the cathode and anode, while in the arc column it is relatively low. The peak of the CuI spectral line intensity near the electrode is caused by electrode evaporation. The peak duration of the CuI spectral line intensity near the cathode is always longer than that near the anode. The CuII spectral line intensity is lower, appears later and disappears earlier, which in the arc column increased obviously, compared with CuI. The CuII density near the cathode is higher than that near the anode, and the CuII density in the arc column is higher than in the two electrodes, which is similar to the axial distribution of electron density. The radial distribution curve of CuI and CuII density is similar to the radial distribution curve of spectral line intensity, and displays the characteristics of a high center and low edge in the radial direction of the arc gap. The difference is that the width of the atomic spectral line is larger than that of the corresponding ionic spectral line, the distribution curve of the ionic spectral line is smooth and symmetrical, and the radial attenuation rate of the CuII density is larger than that of the corresponding CuI. This reflects the ionization of atoms and the effect of magnetic fields. The radial and axial distribution of the particle density is opposite to that of the excitation temperature. Electrode emission will first affect the atom formation.

CAHA/PPAK Integral-field Spectroscopic Observations of M81. II. Testing Photoionization Models in a Spatially Resolved LINER

The origin of the low-ionization nuclear emission-line region (LINER) prevalent in local galaxies and its relationship with supermassive black holes have been debated for decades. We perform a comprehensive evaluation of traditional photoionization models against the circumnuclear ionized gas in M81, for which recent CAHA/PPAK integral-field spectroscopic observations reveal a LINER characteristic out to a galactocentric radius of ∼1 kpc. Constructed with the photoionization code cloudy, the models have the novel aspect of their primary parameters being well constrained by extensive observations of a prototypical low-luminosity active galactic nucleus (LLAGN) and an old stellar bulge in M81. Additionally, these models incorporate a reasonably broad range of uncertain nebular properties. It is found that the integrated photoionization by the LLAGN and hot, low-mass stars distributed in the bulge can roughly reproduce the observed radial intensity distributions of the Hα, Hβ, and [N ii] lines, with the bulge stars dominating the ionizing flux at radii ≳200 pc. However, the models generally fail to reproduce a similarly declining profile of the [O iii] line or an accordingly flat profile of the [O iii]/Hβ ratio. This clearly points to a deficiency of ionizing photons in the outer regions despite an extended photoionization source. The discrepancy might be alleviated if much of the observed [O iii] line arose from a bulge-filling, low-density gas surrounding a denser, Hα-emitting disk, or by a higher AGN luminosity in the recent past. The case of M81 has important implications for the ionization mechanism of LINERs and low-ionization emission-line regions in general.

Experimental study of the transport characteristics of fractional-order vortex beams in a turbulent atmosphere simulator

Fractional vortex beams have attracted increasing attention due to their complex yet intriguing physical properties, such as radial notch intensity distribution and higher degrees of modulation in orbital angular momentum. In this study, we experimentally investigated and compared the beam spread and beam wander characteristics of fractional-order vortex beams with those of integer-order vortex beams after passing through a turbulent atmosphere simulator with varying turbulence intensities. Our results revealed that the beam spread of both fractional-order and integer-order vortex beams increased in a stepwise manner with the topological charge number, indicating that a larger topological charge number resulted in more severe beam spread. Interestingly, we observed that the beam radius of fractional-order vortex beams between two adjacent integer orders initially grew slowly and then rapidly before finally stabilizing into a curvilinear growth trend. This is in contrast to the linear growth trend exhibited by the beam radius of integer-order vortex beams. Furthermore, we found that the growth of the beam radius of half-integer-order vortex beams followed the linear growth trend of the beam radius of integer-order vortex beams. When the integer part of the topological charge was fixed, we observed that stronger turbulence resulted in more severe beam wander for both integer-order and fractional-order vortex beams, with the variance of the center-of-mass drift following the same growth curve. However, when the turbulence intensity is constant, both integer-order and fractional-order vortex beams exhibit a weaker beam wander effect with increasing topological charge. Our findings may provide valuable insights for applications such as optical communication and optical measurement using fractional-order vortex beams.

Generation of structure light in probe absorption spectrum via microwave-driven Y-type atomic system

Behavior of structure light is investigated by monitoring probe absorption using a microwave-driven Y-type atomic media configuration. The system under consideration is driven by one of the control vortex beams as well as an extra non-vortex control beam to ensure electromagnetically induced transparency. The significant aspect in the generation of structured light is the azimuthal phase-dependent modification for probe absorption. Further intensity distribution for absorption spectra is examined for simultaneously evaluating both the control vortex beams. We also go through the radial distribution of intensity for various orbital angular momentum values. Different modes of structural beams may be distinguished using the suggested approach. Our research gives us a way for rapidly transferring vortex wavefronts from control field to probe absorption profile. This could be useful in quantum information processing.

Generation and measurement of irregular polygonal perfect vortex optical beam based on all-dielectric geometric metasurface.

The perfect optical vortex (POV) beam carrying orbital angular momentum with topological charge-independent radial intensity distribution possesses ubiquitous applications in optical communication, particle manipulation, and quantum optics. But the mode distribution of conventional POV beam is relatively single, limiting the modulation of the particles. Here, we originally introduce the high-order cross-phase (HOCP) and ellipticity γ into the POV beam and construct all-dielectric geometric metasurfaces to generate irregular polygonal perfect optical vortex (IPPOV) beams following the trend of miniaturization and integration of optical systems. By controlling the order of the HOCP, conversion rate u, and ellipticity factor γ, various shapes of IPPOV beams with different electric field intensity distributions can be realized. In addition, we analyze the propagation characteristics of IPPOV beams in free-space, and the number and rotation direction of bright spots at the focal plane give the magnitude and sign of the topological charge carried by the beam. The method does not require cumbersome devices or complex calculation process, and provides a simple and effective method for simultaneous polygon shaping and topological charge measurement. This work further improves the beam manipulation ability while maintaining the characteristics of the POV beam, enriches the mode distribution of the POV beam, and provides more possibilities for particle manipulation.

Climatology and changes in internal intensity distributions of global precipitation systems over 2001–2020 based on IMERG

The internal intensity distributions of precipitation systems are closely related to precipitation dynamics. Understanding its climatology and changing characteristics is important for comprehending climate change, enhancing atmospheric model, and obtaining accurate hydrologic responses. However, due to the various limitations of precipitation observations, the internal intensity distributions of global precipitation systems have not been thoroughly investigated. This study uses the Integrated Multi-satellitE Retrievals for Global Precipitation Measurement (IMERG) data during 2001–2020 to investigate the internal intensity distributions of global precipitation systems, by analyzing the climatology and changes in the radial intensity distributions and the core-region intensity of precipitation systems. The results indicate that precipitation systems with larger spatial sizes tend to have higher intensity. Small- and medium-size precipitation systems exhibit the most obvious changes in the inner regions of precipitation systems, with higher intensity during 2001–2010 than 2011–2020. The large-size precipitation systems have slightly higher intensity at each radius of the systems during 2011–2020. Upon further investigation of the core-region intensity of precipitation systems, the small- and medium-size precipitation systems both exhibit significant decreases during 2001–2020 with trends at −1.13 and −2 mm/h per century, respectively. The large-size precipitation systems exhibit nonsignificant increasing trends during 2001–2020. The results also show regional differences, with decreased core-region intensity over most tropical regions and increased core-region intensity over most subtropical regions. This study provides an alternative perspective on the climatology and changing features of precipitation from the system view, and the results revealed could have significant implications on global climate change.

Simultaneous Manipulation of the Temporal and Spatial Behaviors of Nanosecond Laser Based on Hybrid Q-Switching

A hybrid Q-switching method based on a special-shaped saturated absorber was proposed for simultaneous manipulation of the temporal and spatial behaviors of a solid-state pulse laser. The temporal–spatial rate equation model of the laser was given and used to optimize the design parameter of the saturated absorber. Best spatial intensity homogenization performance can be expected using an active-passive hybrid Q-switched laser, comprising a Pockels cell and a cylinder Cr:YAG crystal with one end cut as a spherical concave surface. The optimized laser pulse width could be narrowed to 2.39 ns and the laser radial intensity distribution became quasi-super-Gaussian distribution with a radial intensity distribution ratio of 0.91, while that for the Gaussian beam was 0.84. In principle, the laser coherence can be maintained, and the laser spatial intensity distribution can be kept in a long propagation distance.

The Binary and the Disk: The Beauty is Found within NGC3132 with JWST

The planetary nebula (PN) NGC 3132 is a striking example of the dramatic but poorly understood mass-loss phenomena that (1–8) M ⊙ stars undergo during their death throes as they evolve into white dwarfs (WDs). From an analysis of JWST multiwavelength (0.9–18 μm) imaging of NGC 3132, we report the discovery of an extended dust cloud around the WD central star (CS) of NGC 3132, seen most prominently in the 18 μm image, with a surface-brightness-limited radial extent of ≳2″. We show that the A2V star located 1.″7 to CS’s northeast (and 0.75 kpc from Earth) is gravitationally bound to the latter, as evidenced by the detection of relative orbital angular motion of 0.°24 ± 0.°045 between these stars over ∼20 yr. Using aperture photometry of the CS extracted from the JWST images, together with published optical photometry and an archival UV spectrum, we have constructed the spectral energy distribution (SED) of the CS and its extended emission over the UV to mid-IR (0.091–18 μm) range. We find that fitting the SED of the CS and the radial intensity distributions at 7.7, 12.8, and 18 μm with thermal emission from dust requires a cloud that extends to a radius of ≳1785 au, with a dust mass of ∼1.3 × 10−2 M ⊕ and grains that are 70% silicate and 30% amorphous carbon. We propose plausible origins of the dust cloud and an evolutionary scenario in which a system of three stars—the CS, a close low-mass companion, and a more distant A2V star—forms a stable hierarchical triple system on the main sequence but becomes dynamically unstable later, resulting in the spectacular mass ejections that form the current, multipolar PN.

Generation of multi-channel perfect vortex beams with the controllable ring radius and the topological charge based on an all-dielectric transmission metasurface.

The perfect vortex (PV) beam, characterized by carrying orbital angular momentum and a radial electric intensity distribution independent of the topological charge, has important applications in optical communication, particle manipulation, and quantum optics. Conventional methods of generating PV beams require a series of bulky optical elements that are tightly collimated with each other, adding to the complexity of optical systems. Here, making the amplitude of transmitted co-polarized and cross-polarized components to be constant, all-dielectric transmission metasurfaces with superimposed phase profiles integrating spiral phase plate, axicon and Fourier lens are constructed based on the phase-only modulation method. Using mathematical derivation and numerical simulation, multi-channel PV beams with controllable annular ring radius and topological charge are realized for the first time under circularly polarized light incidence combining the propagation phase and geometric phase. Meanwhile, perfect vector vortex beams are produced by superposition of PV beams under the incidence of left-handed circularly polarized and right-handed circularly polarized lights, respectively. This work provides a new perspective on generating tailored PV beams, increasing design flexibility and facilitating the construction of compact, integrated, and versatile nanophotonics platforms.

Experimental Investigation of the Vortex Dynamics in Circular Jet Impinging on Rotating Disk

A circular jet impinging perpendicularly onto a rotating disk is studied in order to understand the influence of centrifugal forces on the radial wall jet. Time-resolved Particle Image Velocimetry (TR-PIV) measurements are conducted in different jet regions in order to investigate the flow physics of the large-scale vortical structures and the boundary layer development on the impinging wall for both stationary and rotating impinging disks. The Reynolds number is ReD = 2480, the orifice-to-plate distance H = 4D (D is the jet-orifice diameter) and the rotation rate is 200 RPM. It is found that the rotation of the impinging wall results in strong centrifugal effects, which affect different regions of the jet. Both radial velocity profiles and turbulence intensity distributions show different behavior when comparing the stationary and rotating cases. Finite Time Lyapunov Exponent (FTLE) analysis is implemented to describe the time-resolved behavior of the large-scale vortical structures and flow separation.

Concentric ring structure on the front surface of fused silica induced by a focused femtosecond pulse laser

Structural changes of the transparent materials induced by a Femtosecond laser play an important role in the field of femtosecond laser micromachining. In this paper, a concentric ring structure with a period of 2 μm has been observed on the front surface when a single femtosecond pulse was focused at 15 μm below the fused silica surface with an input pulse energy of 2 mJ. A linear correlation between the size of the concentric ring structure and the input pulse energy has been revealed. A model based on the nonlinear Schrödinger equation has been used to calculate the radial light intensity distribution on the fused silica surface. The calculated light intensity distribution and the experimental results are well mapped to each other, which can be expected to provide a new perspective for the exploration of the formation mechanism of the laser-induced concentric ring structure.

Study on Soot Emission Characteristics of Methane/Oxygen Inverse Diffusion Flame.

Inverse diffusion flame (IDF) is an effective and widely used reaction form in the process of noncatalytic partial oxidation (NC-POX) of gaseous hydrocarbons (such as natural gas and coke oven gas). However, soot is generated in the combustion chamber in the case of unreasonable feeding conditions, and thus causes serious damage to the wall and nozzle. In this study, the effects of the equivalence ratio ([O/C]e), the oxygen flow rate, and the Reynolds number on the soot and CH* emission characteristics of CH4/O2 inverse diffusion flame were comprehensively analyzed based on a hyperspectral imaging system. In addition, the relationship between CH* and soot is explored using Ansys Fluent simulation. The experimental results show that the soot radiation core generation area is located in the outer ring of the flame, and the radial distribution of the radiation intensity is bimodal. With the increase in [O/C]e, the initial position for soot radiation and the overall radiation intensity of soot decrease. In addition, the CH* radiation intensity decreases as [O/C]e increases, and CH* exists in the whole flame. The simulation results clearly show that the existence of CH* is conducive to soot production. The emission intensity and the core area of soot formation increase with the increase in the oxygen velocity. Additionally, the soot emission region increases and the flame tip changes from a round blunt to symmetrical tip with the increase in the Reynolds number.

Interconversion of orbital and spin angular momenta of light beams in the CARS generation process in isotropic gyrotropic medium

We investigate the conversion of spin and orbital angular momentum (AM) of elliptically polarized light beams at frequencies ω 1 and ω 2, helical phase profiles, and arbitrary radial intensity distributions to AM of a signal beam at frequency resulting from four-wave mixing process in isotropic gyrotropic medium with spatial dispersion of cubic nonlinearity. Conservation of the total z-projections of both spin and orbital angular momenta of interacting waves is demonstrated. A simple classical and quantum interpretation of validity of the AM conservation law is given.

Development and evaluation of a GEANT4-based Monte Carlo Model of a 0.35 T MR-guided radiation therapy (MRgRT) linear accelerator.

PurposeThe aim of this work was to develop and benchmark a magnetic resonance (MR)‐guided linear accelerator head model using the GEANT4 Monte Carlo (MC) code. The validated model was compared to the treatment planning system (TPS) and was also used to quantify the electron return effect (ERE) at a lung–water interface.MethodsThe average energy, including the spread in the energy distribution, and the radial intensity distribution of the incident electron beam were iteratively optimized in order to match the simulated beam profiles and percent depth dose (PDD) data to measured data. The GEANT4 MC model was then compared to the TPS model using several photon beam tests including oblique beams, an off‐axis aperture, and heterogeneous phantoms. The benchmarked MC model was utilized to compute output factors (OFs) with the 0.35 T magnetic field turned on and off. The ERE was quantified at a lung–water interface by simulating PDD curves with and without the magnetic field for 6.6 × 6.6 cm2 and 2.5 × 2.5 cm2 field sizes. A 2%/2 mm gamma criterion was used to compare the MC model with the TPS data throughout this study.ResultsThe final incident electron beam parameters were 6.0 MeV average energy with a 1.5 MeV full width at half maximum (FWHM) Gaussian energy spread and a 1.0 mm FWHM Gaussian radial intensity distribution. The MC‐simulated OFs were found to be in agreement with the TPS‐calculated and measured OFs, and no statistical difference was observed between the 0.35 T and 0.0 T OFs. Good agreement was observed between the TPS‐calculated and MC‐simulated data for the photon beam tests with gamma pass rates ranging from 96% to 100%. An increase of 4.3% in the ERE was observed for the 6.6 × 6.6 cm2 field size relative to the 2.5 × 2.5 cm2 field size. The ratio of the 0.35 T PDD to the 0.0 T PDD was found to be up to 1.098 near lung–water interfaces for the 6.6 × 6.6 cm2 field size using the MC model.ConclusionsA vendor‐independent Monte Carlo model has been developed and benchmarked for a 0.35 T/6 MV MR‐linac. Good agreement was obtained between the GEANT4 and TPS models except near heterogeneity interfaces.

Influence of Electron Injection on the Characteristics of a Hollow Cathode Glow Discharge

The article presents the results of experimental studies of a glow discharge with a hollow cathode in helium and argon gases using an auxiliary discharge as an electron emitter. The authors proposed to make the electrode common for both discharges in the form of a cylindrical metal mesh. The advantage of this design is explained as follows. The connection between the discharges is carried out through holes in the grid with a geometric transparency of 0.2, which makes it possible not only to smoothly control the glow discharge current, but also to enhance the discharge current. Plasma is known to be one of the most efficient electron emitters; however, its use as a cathode in devices with a glow discharge at low gas pressures is complicated by the fact that a grid with small holes is required to separate the electron flow from the plasma, and it is impractical to use such a system in view of low mechanical strength of the grid Since the hollow cathode works effectively at low gas pressures, the release of an electron flux from the plasma of some auxiliary discharge is possible with much larger holes in the grid separating the plasma and the hollow cathode cavity. In this case, the grid can be made such that it can withstand sufficiently high thermal loads and can operate in typical discharge modes with a hollow cathode. The injection of electrons into the cathode cavity of the glow discharge changes the radial distribution of the glow intensity, the width of the cathode dark space, and other parameters of the plasma in the cathode cavity. The influence of electrons penetrating from the auxiliary discharge into the cathode cavity of the main discharge becomes significant when the current of these electrons is comparable to or exceeds the current of electrons leaving the grid cathode surface as a result of γ-processes. In parallel with the measurement of the optical and electrical characteristics of the hollow cathode glow discharge plasma, measurements of the electron concentration were carried out by the microwave sounding method. The entire current of the auxiliary discharge penetrates into the cavity of the main discharge; however, after acceleration in the cathode dark space, the electrons penetrating from the auxiliary discharge ionize gas atoms and noticeably increase the current of the main discharge. Additional ions formed due to the ionization of the gas by the injected electrons knock out new electrons from the cathode surface, which makes it possible to increase the discharge current.

Reduced volume and reflection for bright optical tweezers with radial Laguerre–Gauss beams

Spatially structured light has opened a wide range of opportunities for enhanced imaging as well as optical manipulation and particle confinement. Here, we show that phase-coherent illumination with superpositions of radial Laguerre-Gauss (LG) beams provides improved localization for bright optical tweezer traps, with narrowed radial and axial intensity distributions. Further, the Gouy phase shifts for sums of tightly focused radial LG fields can be exploited for phase-contrast strategies at the wavelength scale. One example developed here is the suppression of interference fringes from reflection near nanodielectric surfaces, with the promise of improved cold-atom delivery and manipulation.

An improved Gaussian laser beam probability distribution simulation based on Monte Carlo method

Research on target recognition in random media by Monte Carlo method has made rapid progress. However, the commonly used probability sampling function of the emitted photons’ directions is not suitable for simulating the radial cross-sectional distribution of a beam. This sampling has little effect on the simulated laser transmission in clouds, but if the laser range profile (LRP) of a target is simulated, it will cause serious distortion because the common sampling method cannot well represent the radial two-dimensional intensity distribution of the beam. In this paper, the traditional sampling method is improved through rigorous derivation, and the superiority of the method is illustrated by simulation data. The simulation results show that the Monte Carlo model of LRP based on the improved sampling method plays well in profile shape of ideal targets identification. This research can bring more reference and significance to target recognition application.

Electron contamination for 6 MV photon beams from an Elekta linac: Monte Carlo simulation

In external beam radiotherapy, the photons from a linear accelerator (linac) machine undergo multiple interactions, not only in the patient but also in the linac head and the air column between the linac head and the patient. Electrons are released from these interactions and contaminate the beams. The current study evaluates electron contamination for 6 MV photon beams from an Elekta linac using Monte Carlo simulation. The linac head was simulated by the BEAMnrc code and the absorbed dose in a phantom was calculated using the DOSXYZnrc code. The parameters of the initial electron beams on the target, such as mean energy and radial intensity distribution, were determined by matching the calculated dose distributions with the measured dose (at 10 x 10 cm2 field size and 90 cm source-skin distance). The central axis depth-dose curves of electron contamination were calculated for various field sizes from 5 x 5 cm2 to 40 x 40 cm2. We investigated the components that generated the electron contamination for a field size of 10 x 10 cm2. The optimal initial electron beam energy was 6.3 MeV with a full-width half maximum (FWHM) of the radial intensity distribution of 1.0 mm. These parameters were found to be in good agreement with the measured data. Electron contamination increased as the field size increased. At a depth of 1.0 mm and field sizes of 5 x 5, 10 x 10, 20 x 20, 30 x 30, and 40 x 40 cm2, the doses from electron contamination were 3.71, 5.19, 14.39, 18.97 and 20.89 %, respectively. Electron contamination decreased with increased depth. At a depth of 15 mm, the electron contamination was about 1 %. It was mainly generated in the air column between the linac head and the phantom (3.65 %), the mirror (0.99 %), and the flattening filter (0.59 %) (for the depth of 1.0 mm and the field size of 10 x 10 cm2).

Diffraction of (l,n)th mode Laguerre-Gaussian laser beam by a curved fork-shaped grating

The transformation of (l,n)th mode Laguerre-Gaussian (LG) laser beam, in the process of its diffraction by a curved fork-shaped grating with topological charge p, is theoretically studied. The analytical solutions for the diffracted wave field amplitudes are derived in the Fresnel regime and in the back focal plane of a convergent lens. The zeroth-diffraction order is found as (l,n)th mode LG beam. The higher, th diffraction-order beam is described in the radial direction through a product of the Gauss-doughnut function by the double sum of hypergeometric Kummer functions. Its topological charge can be increased or reduced compared to that of the incident beam, or it can be equal to zero. The radial intensity distributions are plotted and compared to the corresponding ones valid when a fork-shaped grating is used. The results are specialized for the cases of incident LG beams of modes (l, n = 0), (l = 0,n) and (l = 0,n = 0) i.e. Gaussian mode.