Annular Distributions Research Articles

Compact multi-ring perfect vortex beam generator fabricated by laser direct writing.

Perfect vortex beams (PVBs) have received much attention in recent years since the annular intensity distributions are independent of the topological charge (TC). However, the cost-effective preparation of micrometer-scale monolithic devices capable of generating multiple PVBs through a simple approach remains a significant challenge. In this work, a design of double-ring perfect spiral phase plates (DPSPPs) is presented for the generation of PVBs at two distinct locations along the radial direction. The respective radii and spacing of the double-ring PVBs can be tuned by changing the control parameters. The proposed DPSPPs are fabricated by the flexible femtosecond laser direct writing (FsDLW) technique. The experimentally generated double-ring vortex beams with different TCs possess an almost constant radius, which is consistent with the characteristics of PVBs. Furthermore, the double-ring PVBs with different fractional and trigonometric function TCs and the multi-ring PVB are also demonstrated. The design and fabrication methods are expected to facilitate the miniaturization of the applications of PVBs in optical manipulation, optical communication, and high-capacity information storage.

Metasurface-based perfect vortex beam for optical eraser

Perfect vortex beams (PVBs) take advantage of conventional vortex beams regarding their property of constant diameter of the annular intensity distribution on different topological charges (TCs), facilitating spatially coupling multiple beams with different TCs simultaneously. However, there are demands for PVBs with larger TCs that can be integrated with CMOS-fabrication processes in applications since conditional PVBs are composed of bulky optical components. In this work, we demonstrate metasurface-based PVBs (MPVBs) with TCs as high as −32 and 16 in the visible, manifesting annular intensity distributions capable of broadband operation. The optical eraser concept by integrating MPVBs has been conducted, and the flower-like interference performs a helicity switch to facilitate the uniformization of ring-shaped intensity profiles for the MPVBs with different TCs. The optical eraser experiments demonstrate the potential of MPVBs in advancing both quantum optics and optical device engineering and pave the way for probing quantum behaviors in optics.

Cutting thick aluminum plates using laser fusion cutting enhanced by dynamic beam shaping

Cutting thick plates is affected not only by the laser power but also by the cut kerf width and the melt flow dynamics that determine the ejection of the molten material. Employing the same laser beam intensity distribution for various thicknesses is the limiting factor when cutting thicker plates. This paper investigates fiber laser fusion cutting of 25 mm thick aluminum with dynamic beam shaping (DBS). While both static and longitudinal dynamic intensity distributions fail to cut this thickness with a 4 kW laser power, a cut through is achieved using annular and elliptical intensity distributions. However, an improvement of 45% in cutting speed can be achieved using an elliptical intensity distribution compared to an annular one. In order to understand the effect of the beam shape, an infrared thermal camera is used to study lateral heat propagation when using different process parameters. Moreover, to analyze the melt flow when changing the DBS frequency, high-speed imaging is utilized to observe the molten material inside the cut kerf. Finally, the cut edge quality is investigated for different cutting conditions.

Independent multicolored bottle-beam generation using acousto-optic spatial shaping of a femtosecond laser beam.

We report on the development of a tunable spectral and spatial frequency shaping system for ultrashort laser pulses using acousto-optic filters. The system enables the creation of arbitrary axially symmetric multi-wavelength field configurations in the Ti:sapphire laser emission range near 800 nm and controlling them at a multi-kilohertz rate. We experimentally demonstrate independent generation of two-colored annular intensity distributions from a single femtosecond laser beam and a bottle beam having the hollow cylindrical volume with the aspect ratio of 9:1. This laser beam shaping system can be useful in creating advanced setups for an optical control of cold atoms.

360-degree directional micro prism array for tabletop flat-panel light field displays.

Tabletop light field displays are compelling display technologies that offer stereoscopic vision and can present annular viewpoint distributions to multiple viewers around the display device. When employing the lens array to realize the of integral imaging tabletop light field display, there is a critical trade-off between the increase of the angular resolution and the spatial resolution. Moreover, as the viewers are around the device, the central viewing range of the reconstructed 3D images are wasteful. In this paper, we explore what we believe to be a new method for realizing tabletop flat-panel light field displays to improve the efficiency of the pixel utilization and the angular resolution of the tabletop 3D display. A 360-degree directional micro prism array is newly designed to refract the collimated light rays to different viewing positions and form viewpoints, then a uniform 360-degree annular viewpoint distribution can be accurately formed. In the experiment, a micro prism array sample is fabricated to verify the performance of the proposed tabletop flat-panel light field display system. One hundred viewpoints are uniformly distributed in the 360-degree viewing area, providing a full-color, smooth parallax 3D scene.

Generalized Terahertz Perfect Vortices with Transmutable Intensity Profiles Based on Spin‐Decoupled Geometric Metasurfaces

AbstractPerfect vortex beams (PVBs) possessing orbital angular momentum (OAM) and constant intensity profile enable practical applications in information encoding and transmission due to an unbounded number of orthogonal OAM channels and fixed annular intensity distributions. Geometric metasurfaces, which are 2D counterparts of metamaterials, have provided an ultra‐compact platform to flexibly design perfect vortex beams in a single flat device. However, the previous reported PVBs based on geometric metasurfaces are limited to ring‐shaped intensity profiles and intrinsic spin‐coupling between two orthogonal spin‐components. Here, spin‐decoupled geometric metasurfaces encoding with two‐step coordinate transformations are proposed to generate helicity‐independent PVBs with transmutable intensity profiles. By tailoring local phase gradient along the azimuthal direction, spin‐independent and polarization‐rotated terahertz (THz) PVBs with CN‐fold rotationally symmetric intensity profiles have been theoretically designed and experimentally demonstrated. Furthermore, THz PVBs with arbitrary intensity profiles have also been realized. The unique approach for simultaneously manipulating the spiral phase, focusing phase, as well as intensity profiles will open a new avenue to develop multifunctional integrated devices and systems, which enables potential applications in information processing and optical communication.

Annular energy and radial dose distributions study for a wide range of ions of different equal LET groups in water

Annular energy distribution, AED is a new concept deduced from radial dose, RDD that enables one to draw a map of energy-dose distribution around the ion's path at the nanometer scale better than the ordinary radial dose. The distribution of energy for different equal LET groups of ions of the same LET (keV/μm) were studied using this concept. Annular energy distributions, AEDs for 185 ions impeded in water medium were studied using Katz radial dose formula. AED was calculated using Butts-Katz and Tabata electron range-energy (R-E) relations and were compared. AED and shell annular energy distribution, SAED for those ions were mapping and confirming that energy distributions for ions of the same LET are not the same. AED growth with annular width r=0.1(nm)⟶Rmin(nm) showing a peak at the maximum annular energy width, rMAEW. Butts-Katz and Tabata show same annular energy distribution peaks of the same value, however, Tabata shows that energy is distributed over a wide range than Butts-Katz. Thus, Butts-Katz R-E relation is recommended and considered. AED for the studied 185 ions shows a peak at certain width called the maximum annular energy width, rMAEW. This rMAEW showed a monotonic increasing function with ion's β2. The total annular energy distribution, TAED for the different ions were determined and it shows a linear increasing function of the ion's (Z*/β)2.

Generation of hollow Gaussian beams by restoring structured light with meta-optics

Hollow Gaussian beams (HGBs) with annular intensity distributions but uniform phase and polarization distributions have aroused enormous interest due to their advantages in optical trapping, optical limiting, etc. Although extensive HGB generation methods have been performed previously, there are still existing limitations in polarization independence and broadband response, which hinder the application of HGBs. Here, we propose and experimentally demonstrate an HGB generation method by restoring structured light with a pair of cascaded dielectric metasurface q-plates. The metasurface q-plates are based on Pancharatnam-Berry (PB) phase and work as elements of optical spin-to-orbital angular momentum conversion. The first metasurface q-plate is used to introduce orbital angular momentum to an incident circularly polarized beam, and the output light field possesses both annular intensity distribution and spiral phase with reversed circular polarization. Since the phase retardation of the metasurface q-plates isπ, the reversed circularly polarized beam output from the first metasurface q-plate will obtain opposite spiral phase after the second metasurface q-plate. Then, the spiral phase of the output light field is counteracted, but its annular intensity distribution is retained as a new HGB. Arbitrarily polarized Gaussian beams are available for incident beams because they can be decomposed into orthogonal circularly polarized components. Furthermore, this method is applicable to a broad spectrum of visible light owing to the dispersion-free characteristic of the PB phase. This work suggests a polarization-independent and broadband HGB generation method, which may benefit HGB-based fundamental research.

Photonic slide rule with metasurfaces

As an elementary particle, a photon that carries information in frequency, polarization, phase, and amplitude, plays a crucial role in modern science and technology. However, how to retrieve the full information of unknown photons in an ultracompact manner over broad bandwidth remains a challenging task with growing importance. Here, we demonstrate a versatile photonic slide rule based on an all-silicon metasurface that enables us to reconstruct incident photons’ frequency and polarization state. The underlying mechanism relies on the coherent interactions of frequency-driven phase diagrams which rotate at various angular velocities within broad bandwidth. The rotation direction and speed are determined by the topological charge and phase dispersion. Specifically, our metasurface leverages both achromatically focusing and azimuthally evolving phases with topological charges +1 and −1 to ensure the confocal annular intensity distributions. The combination of geometric phase and interference holography allows the joint manipulations of two distinct group delay coverages to realize angle-resolved in-pair spots in a transverse manner- a behavior that would disperse along longitudinal direction in conventional implementations. The spin-orbital coupling between the incident photons and vortex phases provides routing for the simultaneous identification of the photons’ frequency and circular polarization state through recognizing the spots’ locations. Our work provides an analog of the conventional slide rule to flexibly characterize the photons in an ultracompact and multifunctional way and may find applications in integrated optical circuits or pocketable devices.

Research on wellbore temperature control and heat extraction methods while drilling in high-temperature wells

During the drilling process, the downhole high-temperature problem has considerably limited the exploration and development of deep oil and gas reservoirs and geothermal resources in China. The aim of its oil and gas exploration and development has gradually shifted to deeper formations. In this study, a transient heat transfer model for high-temperature wells during the drilling process is built. Both heat sources and variations of thermophysical properties of drilling fluids and tubular string with temperature and pressure are considered. An iterative method is used to calculate annular temperature distributions by considering fluid composition, complex casing programs combination, and well structure. Based on the model in this study, a heat extraction-while-drilling technology approach is proposed by combining insulated pipe string and the phase-change heat storage drilling liquid. The results show that this method effectively reduces the bottom-hole temperature while using the geothermal energy of high-temperature wells. The study's results provide a theoretical foundation and technical support for resolving downhole high-temperature complications in deep oil and gas, as well as geothermal well drilling. The results will be a helpful supplement for the petroleum industry in achieving the national energy aim of carbon neutrality and peak carbon dioxide emissions.

Discrete particle simulation of heterogeneous gas-solid flows in riser and downer reactors

The heterogeneous structures of the gas-solid flow in riser and downer reactors determine reactor performance but are not fully understood. This paper presents a numerical study of the hydrodynamic characteristics of cohesive particles in a riser and a downer. This is done by the combined approach of discrete element method (DEM) for particles and computational fluid dynamics (CFD) for the gas phase. The numerical results show that this CFD-DEM model can reproduce different annular dense distributions of particles in the fully developed sections of the riser and downer. This realization requires suitable periodic boundary conditions applied to both the gas and solid phases in the flow direction as well as adequately fine meshes. The flow behaviors are analyzed in detail in terms of particle flow pattern, cluster behaviors, gas and solid velocities and forces acting on particles. Also, the dependence of the dense solid ring in the downer on some pertinent variables related to pipe geometries, material properties, and operational conditions is examined.

Development and application of wellbore heat transfer model considering variable mass flow

Dual-gradient drilling technology is being increasingly used in formations with narrow pressure margins. For dual-gradient drilling based on downhole separation, hollow spheres are separated into the annulus at the separator position, resulting in variable mass flow in the wellbore. Thus, existing heat transfer models are no longer suitable for describing wellbore temperature profiles in dual-gradient drilling. This study focused on developing a wellbore heat transfer model that fully considers separated hollow spheres entering the annulus, complex casing programs, and heat sources, for dual-gradient drilling based on downhole separation. The model was solved using an iterative method. Then, the accuracy of the model was verified using temperature data measured from two wells. Finally, the difference in the annular temperature distributions between dual-gradient drilling and conventional single-gradient drilling were investigated, as were the wellbore heat transfer characteristics for dual-gradient drilling. The following major conclusions were drawn: (1) for dual-gradient drilling based on downhole separation, at the separator location, the annular fluid temperature does not decrease, but rather increase in the flow direction because of the inflow of hollow spheres; (2) a clear inflection point exists in the annular fluid temperature curve at the location where the separator would be; (3) the magnitude of the mutation of the temperature curve at the inflection point is considerably affected by the heat capacities of the hollow spheres and the pure drilling fluid; (4) under the same change in separation efficiency, distance between the bit and separator, flow rate, and thermal conductivity of formation, the variation range of the fluid temperature at the bottom hole is greater than that at the wellhead.

Electrodes Optimization of an Annular Flow Electromagnetic Measurement System for Drilling Engineering

The early monitoring of downhole overflow can be effectively realized by the downhole annular electromagnetic flow detection system. In order to improve the accuracy of the electromagnetic measurement system of downhole annular flow, it is important to optimize the excitation system and electrodes of this system. This research focuses on the optimization of the electrodes for the electromagnetic measurement system of downhole annular flow, whose excitation system has been optimized. First, the basic principle of electromagnetic measurement of downhole annular flow is analyzed. Then, the influence of different positions of the four-point electrodes on the virtual current distributions is analyzed, and the optimum electrode positions and distributions are introduced. On this basis, the influence of shape and size of the large electrode on virtual current density distribution is analyzed. Based on the theoretical study of the influence of electrode on virtual current density distribution, taking hemispherical electrodes and arc electrodes as examples, this paper optimizes hemispherical electrodes and arc electrodes with different shapes and sizes by using finite element simulation method, and proposes three indexes to evaluate the annular virtual current density distributions when the electrodes of different shapes are used. The optimum parameters of shapes and sizes of the hemisphere electrodes and arc electrodes under specific structures of the downhole annular electromagnetic flow measurement system are obtained. This research has great significance for the optimization of electrodes in the downhole annular electromagnetic flow measurement system, and can also be used as reference for the electrode optimization of the traditional electromagnetic flowmeter.

Freeform Lens Design of Beam Shaping With User-Defined Rotation-Symmetric Profile by Using Numerical Method

A freeform lens construction is proposed to form a specific rotation symmetric beam profile with collimation in this paper. In the proposed approach, two freeform surfaces are constructed segment-by-segment using a numerical method based on Snell's law to produce an output beam profile which has both good irradiance uniformity and high collimation. It is shown that as the number of segments used to construct the freeform surfaces increases, the output beam profile approaches the specific profile. A sparse design point freeform surface construction method is additionally proposed which allows the beam profile to approach the desirable distribution with a fewer number of segments. The proposed method is used to construct freeform lenses for producing output beams with two user-defined irradiance patterns, i.e., annular and triangular distributions. The simulation results show that either demonstrated irradiance distribution is close to the specific distribution. Overall, the present results show that the proposed method provides a versatile and efficient approach for designing freeform lenses with a specific distribution of the output beam profile and good collimation.

Ring states in swarmalator systems

Synchronization is a universal phenomenon, occurring in systems as disparate as Japanese tree frogs and Josephson junctions. Typically, the elements of synchronizing systems adjust the phases of their oscillations, but not their positions in space. The reverse scenario is found in swarming systems, such as schools of fish or flocks of birds; now the elements adjust their positions in space, but without (noticeably) changing their internal states. Systems capable of both swarming and synchronizing, dubbed swarmalators, have recently been proposed, and analyzed in the continuum limit. Here, we extend this work by studying finite populations of swarmalators, whose phase similarity affects both their spatial attraction and repulsion. We find ring states, and compute criteria for their existence and stability. Larger populations can form annular distributions, whose density we calculate explicitly. These states may be observable in groups of Japanese tree frogs, ferromagnetic colloids, and other systems with an interplay between swarming and synchronization.

Using a Modular Aperture System to Obtain Annular Dark-Field Image Intensity Distributions as a Function of Scattering Angle.

Using a Modular Aperture System to Obtain Annular Dark-Field Image Intensity Distributions as a Function of Scattering Angle.

Scattering intensity distribution dependence on collection angles in annular dark-field STEM-in-SEM images

A scanning electron microscope (SEM) equipped with a zero-dimensional solid-state transmission electron detector and a modular aperture system was used to examine the relationship between annular dark-field image intensity distributions and several imaging parameters. The effects of primary electron energy, transmission detector acceptance angle and span, and beam convergence angle on scattering intensity distributions exhibited by a 10 nm thick amorphous silicon nitride film were examined. Results showed that angular distributions varied significantly with only minor changes in transmission detector acceptance angle span. Distributions collected with narrow apertures and normalized to acceptance angle span exhibited broad, distinct peaks that shifted to greater angles with decreasing primary electron energy, while even modestly wide apertures resulted in large distribution variations. A comparison between scattering distributions (i.e., diffraction patterns) quantified using the modular aperture system and a two-dimensional pixelated detector demonstrated that equivalent information could be obtained with either detector for this sample.

Using a Modular Aperture System to Obtain Annular Dark-Field Image Intensity Distributions as a Function of Scattering Angle.

Using a Modular Aperture System to Obtain Annular Dark-Field Image Intensity Distributions as a Function of Scattering Angle.

Void fraction and pressure drop in gas-liquid downflow through narrow vertical conduits-experiments and analysis

The present paper investigates void fraction and pressure drop characteristics of vertical air-water downflow through millichannels (0.83≤Eotvos Number≤20.6). Experiments have revealed the hydrodynamics to be a function of tube diameter and phase velocities with the functional form being different for different flow patterns. Accordingly, separate mechanistic models have been proposed to predict the aforementioned parameters for bubbly, slug, falling film and annular flow distributions. The proposed analysis have been validated with experimental results of the present study and those reported in literature.

Modeling of thermal lensing in a [1 1 1]-cut Nd:YAG rod with temperature-dependent parameters and different pumping profiles

Temperature dependences of the thermo-optical coefficients of YAG crystals are often neglected when thermal lensing in laser rods is investigated, though their influence is very significant. It is especially significant for transversally non-uniform thermal loading. An analytical solution of the heat transfer equation with only the radial heat flow is found in the integral form, which is very convenient for numerical simulations. Uniform, top-hat, parabolic, Gaussian, super-Gaussian and annular heat source distributions are used in the calculations. The generalization of the thermally-induced refractive index change for long enough [1 1 1]-cut YAG rods to the case of temperature-dependent YAG parameters is developed and applied to the calculation of the corresponding optical path differences. Different definitions of the optical power of the aberrated thermal lens (TL) are discussed in detail. It is shown that for each of the heat source distributions, the temperature dependences of the YAG parameters significantly increase (1.5–1.8 times) the paraxial optical power of the induced TL.