Large-scale particle trapping by acoustic vortices with a continuously variable topological charge

Strengthened directivity with higher-order side lobes can be generated by the transducer with a larger radius at a higher frequency. The multi-annular pressure distributions are displayed in the cross-section of the acoustic vortices(AVs)which are formed by side lobes. In the near field, particles can be trapped in the valley region between the two annuli of the pressure peak, and cannot be moved to the vortex center. In this paper, a trapping method based on a sector transducer array is proposed, which is characterized by the continuously variable topological charge(CVTC). This acoustic field can not only enlarge the range of particle trapping but also improve the aggregation degree of the trapped particles. In the experiments, polyethylene particles with a diameter of 0.2 mm are trapped into the multi-annular valleys by the AV with a fixed topological charge. Nevertheless, by applying the CVTC, particles outside the radius of the AV can cross the pressure peak successfully and move to the vortex center. Theoretical studies are also verified by the experimental particles trapping using the AV with the continuous variation of three topological charges, and suggest the potential application of large-scale particle trapping in biomedical engineering.

Measuring Topological Charges of Optical Vortices with Multi-Singularity Using a Cylindrical Lens

We present a simple method to measure the topological charges of optical vortices with multiple singularities. Using a cylindrical lens, a vortex beam can decay into a light field distribution with multiple separated dark holes, whose number just equals the topological charge of the input beam. This conclusion is then verified via experiments and numerical simulations of the propagation of vortex beams with multiple singulaxities. This method is also reliable to measure the topological charges of broadband vortex beams with different distributions of singularities, which does not resort to multiple beam interferometrie experiments.

Model-based adaptive locomotion and clustering control of microparticles through ultrasonic topological charge modulation

We present a novel motion control technique for microrobot clusters to exploit the characteristics of the ultrasonic field.The method comprises two steps,i.e.,introducing an ultrasonic actuation(UA)linear model for three-dimensional(3D)locomotion and controlling the topological charge(TC)in the ultrasonic vortex for microrobot clustering.Here,the TC is a controllable parameter for the expansion and contraction of the pressure null space inside the vortex.We present a TC control method to cluster sporadically distributed microrobots in a specific workspace.To validate the concept,a UA system composed of 30 ultrasonic transducers with 1 MHz frequency is fabricated,and the characteristics of the generated acoustic pressure field are analyzed through simulations.Subsequently,the performances of the adaptive controller for precise 3D locomotion and the TC control method for clustering are evaluated.Finally,the UA technology,which performs both clustering and locomotion in a complex manner,is validated with a gelatin phantom in an in-vitro environment.

The global monopole spacetime and its topological charge

We show that the global monopole spacetime is one of the exact solutions of the Einstein equations by treating the matter field as a non-linear sigma model, without the weak field approximation applied in the original derivation by Barriola and Vilenkin. Furthermore, we find the physical origin of the topological charge in the global monopole spacetime. Finally, we generalize the proposal which generates spacetime from thermodynamical laws to the case of spacetime with global monopole charge.

Settled fast measurement of topological charge by direct extraction of plane wave from vortex beam

A method of measuring the vortex beam topological charge(TC)is proposed based on a device that can directly extract the plane wave form from the vortex beam in which the different propagation angles of the plane waves are uniquely related to the different TCs.Then the TC can be obtained by simply comparing the energy values perceived by two fixed sensors in the detection location with the help of twin omnidirectional energy absorbers(OEAs).Because the settled detection relies only on the simple quantitative value at two fixed positions,neither pattern recognition nor field analysis procedure is applied,thus allowing faster measurement.Some features of the methodology are investigated,and the numerical simulations verify the feasibility and robustness of the system.

Arbitrary topological charge vortex beams from carbon dots random lasers

Vortex beams have attracted great attention due to their promising applications in the fields of high-capacity optical communication,optical micromanipulation,and quantum information processing.Here,we demonstrate vortex beams with flexible control of the topological charge and modes in a carbon dots random laser for the first time.Vortex beams with different types,including the Laguerre-Gaussian(LG),Bessel-Gaussian(BG),LG-superposition,and polarized vortex beams with topological charges up to 50,have been successfully achieved.Moreover,vortex beams can be well realized in carbon dots random lasers with different emission wavelengths covering from 465 to 612 nm.This work would not only enrich the types of vortex laser,especially for solution-processable lasers,but also provide a new route to realizing multicolor and wavelength-tunable vortex lasers.

Generating large topological charge Laguerre–Gaussian beam based on 4K phase-only spatial light modulator

The resolution of the spatial light modulator(SLM)screen and the encoding algorithm of the computer-generated hologram are the primary limiting factors in the generation of large topological charge vortex beams.This paper attempts to solve these problems by improving both the hardware and the algorithm.Theoretically,to overcome the limitations of beam waist radius,the amplitude profile function of large topological charge Laguerre–Gaussian(LG)beam is properly improved.Then,an experimental system employing a 4K phase-only SLM is set up,and the LG beams with topological charge up to 1200 are successfully generated.Furthermore,we discuss the effect of different beam waist radii on the generation of LG beams.Additionally,the function of the LG beam is further improved to generate an LG beam with a topological charge as high as1400.Our results set a new benchmark for generating large topological charge vortex beams,which can be widely used in precise measurement,sensing,and communication.

Spin-orbit-locked hyperbolic polariton vortices carrying reconfigurable topological charges

The topological features of optical vortices have been opening opportunities for free-space and on-chip photonic technologies,e.g.,for multiplexed optical communications and robust information transport.In a parallel but disjoint effort,polar anisotropic van der Waals nanomaterials supporting hyperbolic phonon polaritons(HP2s)have been leveraged to drastically boost light-matter interactions.So far HP2 studies have been mainly focusing on the control of their amplitude and scale features.Here we report the generation and observation of mid-infrared hyperbolic polariton vortices(HP2Vs)associated with reconfigurable topological charges.Spiral-shaped gold disks coated with a flake of hexagonal boron nitride are exploited to tailor spin-orbit interactions and realise deeply subwavelength HP2Vs.The complex interplay between excitation spin,spiral geometry and HP2 dispersion enables robust reconfigurability of the associated topological charges.Our results reveal unique opportunities to extend the application of HP2s into topological photonics,quantum information processing by integrating these phenomena with single-photon emitters,robust on-chip optical applications,sensing and nanoparticle manipulation.

Experimental realization to efficiently sort vector beams by polarization topological charge via Pancharatnam–Berry phase modulation

This paper reports the experimental realization of efficiently sorting vector beams by polarization topological charge （PTC）. The PTC of a vector beam can be defined as the repetition number of polarization state change along the azimuthal axis, while its sign stands for the rotating direction of the polarization. Here, a couple of liquid crystal Pancharatnam-Berry optical dements （PBOEs） have been used to introduce conjugated spatial phase modulations for two orthogonal circular polarization states. Applying these PBOEs in a 4-foptical system, our experiments show the setup can work for PTC sorting with a separation efficiency of more than 58%. This work provides an effective way to decode information from different PTCs, which may be interesting in many fields, especially in optical communication.

Probing the fractional topological charge of a vortex light beam by using dynamic angular double slits

Vortex beams with fractional topological charge(FTC) have many special characteristics and novel applications.However, one of the obstacles for their application is the difficulty of precisely determining the FTC of fractional vortex beams. We find that when a vortex beam with an FTC illuminates a dynamic angular double slit(ADS), the far-field interference patterns that include the information of the FTC of the beam at the angular bisector direction of the ADS vary periodically. Based on this property, a simple dynamic ADS device and data fitting method can be used to precisely measure the FTC of a vortex light beam with an error of less than 5%.

Measuring the topological charge of optical vortices with a single plate

Measuring the topological charge(TC) of optical vortex beams by the edge-diffraction pattern of a single plate is proposed and demonstrated. The diffraction fringes can keep well discernible in a wide three-dimensional range in this method. The redundant fringes of the diffracted fork-shaped pattern in the near-field can determine the TC value, and the orientation of the fork tells the handedness of the vortex. The plate can be opaque or translucent, and the requirement of the translucent plate for TC measurement is analyzed. Measurement of TCs up to ±40 is experimentally demonstrated by subtracting the upper and lower fringe numbers with respect to the center of the light. The plate is easy to get, and this feasible measurement can bring great convenience and efficiency for researchers.

Dependence of overlap topological charge density on Wilson mass parameter

In this paper,we analyze the dependence of the topological charge density from the overlap operator on the Wilson mass parameter in the overlap kernel by the symmetric multi-probing source(SMP)method.We observe that non-trivial topological objects are removed as the Wilson mass is increased.A comparison of topological charge density calculated by the SMP method using the fermionic definition with that of the gluonic definition by the Wilson flow method is shown.A matching procedure for these two methods is used.We find that there is a best match for topological charge density between the gluonic definition with varied Wilson flow time and the fermionic definition with varied Wilson mass.By using the matching procedure,the proper flow time of Wilson flow in the calculation of topological charge density can be estimated.As the lattice spacing a decreases,the proper flow time also decreases,as expected.

High-harmonic-generation-inspired preparation of optical vortex arrays with arbitrary-order topological charges

In the process of high-harmonic generation with a Laguerre-Gaussian （LG） mode, it was well established that the topological charge could be of an N-fold increase due to angular momentum conservation. Here, by mimicking the effect of high-harmonic generation, we devise a simple algorithm to generate optical vortex arrays carrying arbitrary topological charges with a single phase-only spatial light modulator. By initially preparing a coaxial superposition of suitable low-order LG modes, we demonstrate experimentally that the topological charges of the embedded vortices can be multiplied and transformed into arbitrarily high orders on demand, while the array structure remains unchanged. Our algorithm offers a concise way to efficiently manipulate the structured light beams and holds promise in optical micromanipulation and remote sensing.

Competition of Quantum Anomalous Hall States and Charge Density Wave in a Correlated Topological Model

We investigate the topological phase transition driven by non-local electronic correlations in a realistic quantum anomalous Hall model consisting of d_(xy)–d_(x^(2)-y^(2)) orbitals. Three topologically distinct phases defined in the noninteracting limit evolve to different charge density wave phases under correlations. Two conspicuous conclusions were obtained: The topological phase transition does not involve gap-closing and the dynamical fluctuations significantly suppress the charge order favored by the next nearest neighbor interaction. Our study sheds light on the stability of topological phase under electronic correlations, and we demonstrate a positive role played by dynamical fluctuations that is distinct to all previous studies on correlated topological states.

Study of Topological Structure of Vacuum by Lattice QCD

Overlap fermions and improved 5Li cooling are compared, which exhibits that these two filter methods can produce similar structures. Then the overlap fermions and improved 5Li cooling are combined to calculate the topological charge and identify the structure of the vacuum. The results are consistent with instanton liquid model .

Performance analysis of single-focus phase singularity based on elliptical reflective annulus quadrangle-element coded spiral zone plates

Optical vortices generated by the conventional vortex lens are usually disturbed by the undesired higher-order foci,which may lead to additional artifacts and thus degrade the contrast sensitivity. In this work, we propose an efficient methodology to combine the merit of elliptical reflective zone plates(ERZPs) and the advantage of spiral zone plates(SZPs) in establishing a specific single optical element, termed elliptical reflective annulus quadrangle-element coded spiral zone plates(ERAQSZPs) to generate single-focus phase singularity. Differing from the abrupt reflectance of the ERZPs, a series of randomly distributed nanometer apertures are adopted to realize the sinusoidal reflectance. Typically, according to our physical design, the ERAQSZPs are fabricated on a bulk substrate;therefore, the new idea can significantly reduce the difficulty in the fabrication process. Based on the Kirchhoff diffraction theory and convolution theorem, the focusing performance of ERAQSZPs is calculated. The results reveal that apart from the capability of generating optical vortices,ERAQSZPs can also integrate the function of focusing, energy selection, higher-order foci elimination, as well as high spectral resolution together. In addition, the focusing properties can be further improved by appropriately adjusting the parameters, such as zone number and the size of the consisted primitives. These findings are expected to direct a new direction toward improving the performance of optical capture, x-ray fluorescence spectra, and forbidden transition.

Terahertz quasi-perfect vortex beam with integer-order and fractional-order generated by spiral spherical harmonic axicon

We propose a new method to generate terahertz perfect vortex beam with integer-order and fractional-order. A new optical diffractive element composed of the phase combination of a spherical harmonic axicon and a spiral phase plate is designed and called spiral spherical harmonic axicon. A terahertz Gaussian beam passes through the spiral spherical harmonic axicon to generate a terahertz vortex beam. When only the topological charge number carried by spiral spherical harmonic axicon increases, the ring radius of terahertz vortex beam increases slightly, so the beam is shaped into a terahertz quasi-perfect vortex beam. Importantly, the terahertz quasi-perfect vortex beam can carry not only integer-order topological charge number but also fractional-order topological charge number. This is the first time that vortex beam and quasi-perfect vortex beam with fractional-order have been successfully realized in terahertz domain and experiment.

Spatial quantum coherent modulation with perfect hybrid vector vortex beam based on atomic medium

The perfect hybrid vector vortex beam(PHVVB)with helical phase wavefront structure has aroused significant concern in recent years,as its beam waist does not expand with the topological charge(TC).In this work,we investigate the spatial quantum coherent modulation effect with PHVVB based on the atomic medium,and we observe the absorption characteristic of the PHVVB with different TCs under variant magnetic fields.We find that the transmission spectrum linewidth of PHVVB can be effectively maintained regardless of the TC.Still,the width of transmission peaks increases slightly as the beam size expands in hot atomic vapor.This distinctive quantum coherence phenomenon,demonstrated by the interaction of an atomic medium with a hybrid vector-structured beam,might be anticipated to open up new opportunities for quantum coherence modulation and accurate magnetic field measurement.

Robust measurement of orbital angular momentum of a partially coherent vortex beam under amplitude and phase perturbations

The ability to overcome the negative effects,induced by obstacles and turbulent atmosphere,is a core challenge of long-distance information transmission,and it is of great significance in free-space optical communication.The spatial-coherence structure,that characterizes partially coherent fields,provides a new degree of freedom for carrying information.However,due to the influence of the complex transmission environment,the spatial-coherence structure is severely damaged during the propagation path,which undoubtedly limits its ability to transmit information.Here,we realize the robust far-field orbital angular momentum(OAM)transmission and detection by modulating the spatial-coherence structure of a partially coherent vortex beam with the help of the cross-phase.The cross-phase enables the OAM information,quantified by the topological charge,hidden in the spatial-coherence structure can be stably transmitted to the far field and can resist the influence of obstructions and turbulence within the communication link.This is due to the self-reconstruction property of the spatial-coherence structure embedded with the cross-phase.We demonstrate experimentally that the topological charge information can be recognized well by measuring the spatial-coherence structure in the far field,exhibiting a set of distinct and separated dark rings even under amplitude and phase perturbations.Our findings open a door for robust optical signal transmission through the complex environment and may find application in optical communication through a turbulent atmosphere.

Average Capacity of OAM-Multiplexed FSO System with Vortex Beam Propagating Through Non-Kolmogorov Turbulence

The propagation of vortex beam in atmospheric turbulence is of significant importance in theoretical study and practical applications. Based on extended Huygens-Fresnel integral and the Rytov approximation, the average capacity of orbital angular momentum(OAM)-multiplexed Laguerre-Gaussian(LG) beam propagating through non-Kolmogorov turbulence is presented, and the analytical expression of spiral spectrum of LG beam has been deduced. The average capacity of FSO system is numerically calculated and the influence of exponent parameter, transmission height, structure constant, wavelength, outer scale and inner scale on average capacity are also analyzed in detail. Outcomes show that smaller structure constant, outer scale, higher transmission height and larger wavelength, inner scale are conducive to improve average capacity in different extent. Results acquires in this paper have potential application value in optical communication within non-Kolmogorov turbulence.