Topological textures of spin vectors are fundamentally interesting and possess generic features for various vector waves. However, experimental realizations of spin skyrmions are mostly restricted to magnetic materials and optical waves, which remains a significant challenge for airborne sound waves with intrinsic curl-free features. In this work, we propose a concentric cylindrical metastructure to construct spin skyrmion textures with subwavelength scale excited by an acoustic spin source. By acoustic spin-orbital coupling, we achieve multi-order confined Bessel spoof acoustic surface waves with orbital angular momentum on the metastructure surface, experimentally observe the acoustic spin skyrmion configurations with subwavelength scale, and verify the topologically protection for introducing the defects. The achievement of acoustic spin skyrmions not only expands the family of topological textures in sound but also provides an avenue to manipulating small particles by controlling structural acoustic fields.

In this study,the radially polarized partially coherent Gaussian vortex array(RPPCGVA)beam is constructed by introducing the multiple off-axis vortex phase into the center of each sub-lobe of partially coherent Gaussian array beam,and the focusing properties of the beam through a thin lens are investigated.The experimental results show that the RPPCGVA beams with different numbers of vortex arrays will gradually merge from the initial array beam into a single beam in the focus process due to its spatial correlation between the sub-beams,and present polygonal hollow,flat-top,and Gaussian-like distributions in the focal plane,respectively.In addition,the polarization state of the beam is gradually transformed from the initial radial polarization into an inverted triangle,oblique square,pentagon,etc.elliptical polarization distribution due to the effect of multiple off-axis vortex phases.However,the beam's intensity degrades to Gaussian distribution,and its polarization state degrades to an elliptical polarization distribution with circular symmetry when the coherence is very low.In addition,the beam still has strong self-healing ability when one of the sub-beams is partially blocked by a sectoral obstacle,but it will be destroyed for completely blocking,resulting in a distortion for the intensity and its state of polarization.

Acoustic skyrmion modes are topological texture structures of velocity field vectors generated on the surface of acoustic structures.This protected vector distribution provides new opportunities for processing sound information,transmission,and data storage.In this study,a combined structure of waveguides and spiral structures is designed by using directional acoustic sources to excite waveguide mode transmission,thereby achieving selective excitation of localized acoustic skyrmion modes.Through theoretical analysis and numerical simulations,the pressure field distribution and velocity field distribution excited by spin acoustic sources,Huygens acoustic sources,and Janus acoustic sources in this structure are investigated,demonstrating the directional transmission properties of acoustic surface waves and the selectively excited acoustic skyrmion modes in the combined structure.Numerical calculations reveal that when the spin acoustic source excites acoustic surface waves propagating along the waveguide,the acoustic skyrmion modes in the helical structure in the direction corresponding to the propagation are selectively excited.When the Huygens source excites acoustic surface waves propagating along the waveguide,the acoustic skyrmion modes in the right or left direction are selectively excited.However,when the Janus source excites acoustic surface waves propagating along the waveguide,the acoustic skyrmion modes in the upward or downward direction are selectively excited.This selective excitation of acoustic skyrmion modes by a directional acoustic source provides a new way to design advanced acoustic information processing functional devices.

In recent years, the discovery of the transverse spin of acoustic wave in a structural acoustic field and acoustic structural surface wave has expanded our knowledge of the basic characteristics of acoustic waves and opened up new avenues for their manipulation. On the structured surface, however, the distribution of acoustic surface waves often presents a uniform distribution, which restricts the local modification of acoustic spin angular momentum and particle manipulation capabilities. In this study, we develop some acoustic waveguides with gradients that are flat, up-convex, and down-concave in order to manipulate the lateral spin distributions of acoustic surface waves. We verify the direction-locking near-field acoustic spin-momentum, explore the pressure field distribution and the spin angular momentum density distribution of a spin acoustic source excited in each of the three gradient structures, and we also show how to manipulate the spin intensity distributions of acoustic surface waves in the gradient waveguides through theoretical analysis and numerical simulation. The numerical calculation results show that when the acoustic surface wave is excited by a clockwise rotating spin source and propagates along the left side of the waveguide, the spin angular momentum density is positive on the upper surface of the structured waveguide and negative on the lower surface. The spin angular momentum distribution and the direction of propagation of acoustic wave are entirely changed when the spin source is rotated counterclockwise. Specifically, an unequal distribution of acoustic spin angular momentum is produced by the upper convex-type waveguide and bottom concave-type waveguide when we convert the flat-type acoustic structure waveguide into a gradient-type waveguide. According to the computation results, the down-concave type waveguide exhibits a stronger density of acoustic spin angular momentum at the end and the acoustic surface waves gather at the end of the constructed waveguide. On the other hand, the waveguide collects acoustic waves close to the structure center when it is an up-convex structural waveguide. The findings can open up new avenues for manipulating particles using acoustic waves, by providing a means for controlling the acoustic spin angular momentum density and improving our understanding of symmetry in acoustic near-field physics.

In this paper, we investigate the propagation properties of radially polarized rectangular-symmetric cosine-Gaussian Schell-model (RCGSM) beam with multiple off-axis vortex phases by using Fourier transform and convolution method based on the unified theory of coherence and polarization. The results indicate that the radially polarized RCGSM beam has self-splitting properties and can be split into four identical lobes due to its unique spatial coherence structure. Furthermore, the modulation of multiple off-axis vortex phases can be acted on each lobe. For high coherence, the spot arrays with triangular or square hollow light intensity distribution can be generated in the focal plane by modulating the number of off-axis vortices (N0) and the beam order, and the corresponding state of polarization on each lobe presents an inverted triangular or oblique square elliptic distribution. However, for small coherence, the modulation effect of multiple off-axis vortex phases disappears and the light intensity of each lobe degenerates into a quasi-Gaussian distribution, whereas its state of polarization keeps invariant, which is independent of the beam order and coherence length. In addition, the beam still has a certain self-healing ability for one of the off-axis vortex phases partially blocked by an obstacle, but it will be destroyed for completely blocking, resulting in a notch on each lobe.

In this paper, a new theoretical model of a partially coherent Laguerre–Gaussian (LG) beam carrying multiple off-axis vortex phases was established. The evolution properties of the focused intensity of the beam after passing through a thin lens were theoretically studied, and then the modulation effect of multiple off-axis vortex phases on the beam with multiring structured intensity was explored. The results indicate that the multiple off-axis vortex phases can reconstruct the multiring structured intensity within the LG beam, thus generating a structured intensity with multilobe and multiring patterns. What is more, the intensity distribution of the lobes between two adjacent rings is complementary, and its number is related to the number and topological charge of off-axis vortex phases. However, with a decrease in the coherence, such a multilobe and multiring structured intensity distribution disappears, gradually evolves into a polygonal flat-topped distribution, and finally degenerates into a quasi-Gaussian distribution. This work demonstrates the effective regulation of multiple off-axis vortex phases on a beam with a multiring structured intensity and indicates that regulating the multiple off-axis vortices provides an additional degree of freedom for optical field modulation, which will have potential applications in the fields of optical micromanipulation and optical information storage.

In quantum systems, a counterintuitive phenomenon known as quantum Zeno dynamics is usually exploited to tailor and protect the coherent evolution of quantum states by the back action of quantum measurements and strong couplings. Here, with the quantum-classical analogy, we report that the acoustic Zeno dynamics can be reproduced in acoustic waveguide arrays by setting segmented waveguides. We experimentally demonstrate that the segmented waveguide acts as an acoustic barrier to tailor the whole Hilbert space into different subspaces by separating the communication between waveguides. By arranging the acoustic Zeno barriers, we can control the sound transport in waveguide arrays into the target output ports, such as the Zeno dynamics, analog-quantum walk, and analog-quantum logic gates. In this context, we highlight that the Zeno barrier can be a versatile tool to arbitrarily control and guide the sound transport in waveguide arrays, which can provide an alternative choice for acoustic metamaterials and metasurfaces without cumbersome and complicated structure design. The acoustic Zeno barrier may provide a versatile approach to manipulate acoustic wave propagation for designing advanced on-chip integrated sound devices.

In this work, a new kind of partially coherent vector beam, namely, partially coherent radially polarized multi-Gaussian Schell-model array (PCRP MGSMA) beam, is introduced and the focusing properties of such beam passing through a thin lens are characterized. One of the most remarkable features of such beam is its capability of producing tunable multifocal spot arrays in the focal plane, and each array lobe can be shaped into dark hollow, Gaussian-like and flat-topped profile by modulating the initial spatial coherence width More interesting, the modulation effect of multiple off-axis vortices can also be acted on each array lobe, thus the creation of triangle-like, square-like and pentagon-like hollow structure arrays can be realized for the high coherence case, but this remarkable characteristic will be vanished in the case of a very low coherence. In addition to the focal spot arrays tailoring, the focal intensity distribution of such beam can be flexibly shaped into diversified flat-topped profiles, such as linear, square and rectangular, by elaborately choosing the matching parameters of the source. These interesting results will be useful for optical multi-particle manipulation, high resolution imaging and material surface processing.

In recent years, the partially coherent beam carrying the twisted phase has received extensive attention due to its unique properties. A new partially coherent vector beam endowed with a twisted phase and a special spatial correlation structure is introduced, which is radially polarized twisted rectangular multi-Gaussian Schell-model beam. The cross-spectral density matrix elements of such beam passing through the ABCD optical system were derived, and the evolution properties, such as the normalized intensity distribution, the spectral degree of coherence (SDOC), and the spectral degree of polarization (SDOP) were investigated in detail. Numerical results show that the intensity distribution of the radially polarized rectangular multi-Gauss Schell-model beam without the twist phase gradually evolves from the hollow ring profile in the source plane into the rectangular flat-top profile in the focal plane. In comparison, the twisted phase carried by the radially polarized twisted rectangular multi-Gaussian Schell-model beam will not only induce the rotation of the beam spot, but also cause a series of changes in the SDOC and SDOP of the beam during the propagation process. The research results provide some theoretical guidance for the control of new vector structured beams with twisted phases, and have potential applications in beam shaping, optical micro-manipulation, and free space optical communications.

A general form of twisted Hermite Gaussian Schell-model (THGSM) beams is introduced; analytical expressionsare obtained for cross-spectral density and M2-factor using the extended Huygens-Fresnel principle and Wigner function. The evolution of THGSM beams during propagation in non-Kolmogorov turbulence is shown numerically; the beams exhibit self-splitting and twist into two lobes. The intensity distribution evolves into a Gaussian shape and beam quality worsens with increasing distance; the intensity distribution and M2-factor are determined by the twist factor, beam orders, and other beam parameters. THGSM beams provide more degrees of freedom to regulate beam parameters, thereby enriching the types of partially coherent beams.

In order to explore the capture of two types of particles with different refractive-indexes with focused partially coherent Lommel-Gaussian beam (PCLGB), we numerically derived the expressions of the intensity, and its distribution is also simulated. We found that the focused PCLGB is able to capture two high refractive-index particles at different positions on the focal plane and a low refractive-index particle at the focus, respectively. when the orbital angular momentum（OAM）quantum number, lens focal length, asymmetry parameter decreased, and the spatial correlation length and beam waist increased, the transverse gradient force of the focused PCLGB increased; when the OAM quantum number, lens focal length, asymmetry parameter, spatial correlation length decreased and the beam waist increased, the axial gradient force and scattering force of the focused PCLGB increased. We can choose the optimum optical and lens parameters, a large range and stable trapping can be achieved. The obtained results have certain reference value for the focused PCLGB applied in micromanipulation technology and biotechnology.

Based on the Snyder-Mitchell linear model and the cross-spectral density (CSD) function, the analytical propagation formula of twisted Gaussian Schell-model (TGSM) beams in strongly nonlocal nonlinear medium (SNNM) is derived. Then the propagation characteristics of TGSM beam are studied. It is found that the soliton radius is jointly determined by the initial power, coherence length, and twist factor; the degree of spatial coherence is adjusted by changing the twist factor without affecting the soliton intensity. In the case of non-soliton properties, there is a threshold of coherence length which makes partially coherent beams have the same evolution law as completely coherent beams. Furthermore, increasing the twist factor, decreasing the coherence length and initial power can improve the beam quality of the beam propagating in SNNM.

We first introduce a class of a superimposed Hermite-Gaussian-correlated Schell model with a multiple off-axis vortices beam, with the side lobe of the beam carrying one to four vortex singularities at the source plane. Subsequently, the variation laws of this beam after being focused by a thin lens are studied theoretically to obtain the optimal beam parameters. The numerical simulation results show that the beam possesses a unique multiple vortex structure, phase structure, and orbital angular momentum. Its intensity resembles a spiral staircase rotating around the axes. The rotational symmetry property of the transverse energy flow along the z axis was broken by the vortices. The hot spot position can be adjusted flexibly by changing the off-axis distance of vortices. This study is of great significance for nondestructive capture and manipulation of multiple particles or cells.

A class of random, wide-sense stationary optical beams with uniform correlations, named the partially coherent quasi-rectangular beam, is introduced theoretically. Based on the extended Huygens-Fresnel principle, the analytical expressions for the cross-spectral density (CSD), effective radius of curvature, and beam wander of the beam in the non-Kolmogorov turbulence are derived. It is found that the position of maximum intensity of the partially coherent quasi-rectangular beams shifts farther from the axis at intermediate distance, the shift in the turbulence is depressed compared to that in free space. As the effective radius of curvature decreases from infinity to a constant with the increase of the coherence length, it always takes a higher value than that in free-space propagation when the other parameters are fixed. In addition, the beam wander can be reduced by picking a relative small initial beam width, short coherence length, or long wavelength. These results are of importance for optical systems operating through long-range turbulent channels in which a beam must have a range-dependent tilt, e.g. on travelling around an obstacle on the axis.

In this paper, we propose a generalized kind of partially coherent vector beams with an off-axis vortex, named partially coherent radially polarized (PCRP) off-axis vortex beam for considering such a case in which laser beam passes through a spiral phase plate (SPP) but slightly deviates from the vortex core due to the experimental misoperation. The influences of such off-axis vortex phase on the focusing properties of the PCRP off-axis vortex beam after passing through a thin lens are theoretically investigated in detailed. It is found that the intensity pattern of the PCRP off-axis vortex beam possesses an additional dark core corresponding to the off-axis position of vortex core in the source plane, while it rotates gradually up to an angle of π∕2 with respect to the initial displacement vectors as propagation distance increases for high spatial coherence, being qualitatively different from that of the on-axis vortex beam. However, such unique characteristics of the PCRP off-axis vortex beam will disappear in the case of a very low coherence. In addition, the vortex-induced changes of polarization start from its off-axis vortex core, which will be useful for the detection of a phase object as well as its vortex position in the application of optical detection technology. More importantly, our results show that, besides the topological charge and coherence length, the off-axis parameters of vortex phase play a great role in modulating the propagation properties, which provides an additional degree of freedom for focus shaping.

为了探究部分相干Airy涡旋光束在非Kolmogorov谱中模态强度的演化规律,基于广义的Huygens-Fresnel原理和Rytov近似理论,推导了部分相干Airy涡旋光束的轨道角动量模态概率的解析式.结合MATLAB的数值模拟,研究了部分相干Airy涡旋光束在非Kolmogorov谱湍流大气中传输时湍流参量和波束参量与涡旋模态强度的关系,对部分相干Airy涡旋光束的相干宽度在传输过程中对模态强度的影响进行了理论分析.结果表明,选取拓扑荷数较小、主亮环半径较大、波长较长的部分相干Airy涡旋光束能有效减缓湍流效应的影响,减小强湍流中模态间的串扰;较大的湍流谱幂指数和较小的探测器孔径直径能提高部分相干Airy涡旋光束的模态强度;与完全相干涡旋光束相比,部分相干涡旋光束具有较强的湍流阻力,在大气湍流中能有更好的传输性能,相干性较差会导致螺旋谱分布弥散.这些结果对自由空间光通信的研究具有一定的参考价值.

The evolution properties of the normalized intensity distribution, the spectral degree of coherence (SDOC), and the spectral degree of polarization (SDOP) of a radially polarized Laguerre-Gaussian correlated Schell-model (LGCSM) beam propagating in turbulent atmosphere has been studied in detail. Based on the extended Huygens-Fresnel integral and the unified theory of coherence and polarization, analytical formulas for the elements of the cross-spectral density (CSD) matrix of a radially polarized LGCSM beam in turbulent atmosphere are derived. Numerical results show that the normalized intensity distributions of the radially polarized LGCSM beams gradually evolve from a doughnut shape into a solid spot and become a Gaussian beam profile eventually due to the anisotropic effect of atmospheric turbulence on propagation. Furthermore, the influences of the spatial coherence length, the structure constant of the refractive-index fluctuations of the turbulence, the power index, the inner scale of the turbulence and the outer scale of the turbulence on the propagation properties of the normalized intensity distributions, the SDOC, and the SDOP of the radially polarized LGCSM beams are discussed in detail.

A new kind of partially coherent vector vortex beam, namely, the partially coherent radially polarized (PCRP) beam with multiple off-axis vortices, is introduced, and the average intensity distributions of such vortex beam focused by a thin lens are investigated theoretically. It is novelty that the off-axis vortices will induce the focal intensity redistribution and reconstruction, while this remarkable characteristic will be vanished in the case of a very low coherence. In view of this distinctive feature, a new method has been put forward to shape or modulate the focal intensity distribution by elaborately tailoring the multiple off-axis vortices as well as the coherence length. More importantly, some peculiar focal fields with novel structures, such as bar-shaped, triangle-shaped, square-shaped, and pentagon-shaped hollow profiles or flat-top foci, are obtained. Our results indicate that modulating the multiple off-axis vortices provides an additional degree of freedom for focus shaping.

In this paper, we discuss, both analytically and numerically, the paraxial propagation of the radially polarized Laguerre-Gaussian-correlated Schell-model (LGCSM) beams orthogonal to the optical axis in uniaxial crystals. The analytical expression for the cross-spectral density function and the second-order moments of the radially polarized LGCSM beams are derived, and the evolution properties of the normalized intensity distribution, the spectral degree of the coherence (SDOC), and the spectral degree of the polarization (SDOP) in uniaxial crystals are elucidated by numerical examples. It is found that the intensity distribution of the radially polarized LGCSM beams evolves from a doughnut shape into a solid shape and finally converts into an elliptical symmetric hollow-ring profile in uniaxial crystals due to the combined effect of special correlation functions and the anisotropy effect of the uniaxial crystals. The evolution of the SDOC and SDOP for the radially polarized LGCSM beams is quite different from that of the radially polarized Gaussian-Schell-model beams. In addition, the propagation properties of the radially polarized LGCSM beams are closely related to the spatial coherence length, the mode order, and the ratio of extraordinary and ordinary reflective indices. The results show that the uniaxial crystals could modulate the evolution properties of the radially polarized LGCSM beams.

光束在大气湍流中传输时,可通过调节部分相干光束的空间关联结构实现传输性质的调控.在总结特殊关联部分相干光束大气湍流传输相关基本理论的基础上,分别介绍了特殊关联部分相干光束的产生方法以及空间关联结构的测量方法,讨论了特殊关联部分相干光束在大气中传输所产生的物理效应,对于激光大气传输有一定的参考价值.