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Given the significant progress in the field of meta-lenses over the past decade, tunable meta-lenses have garnered considerable attention for their flexible functionality. Various mechanisms have been developed to realize high-performance tunable meta-lenses, including electricity, strain, thermal effects, and materials, such as phase-change materials and liquid crystals. However, currently, most tunable meta-lenses are limited to discrete focal lengths, typically only involving two spots, and the potential of phase-change materials, such as Ge2Sb2Te5, Sb2S3, etc., has not yet been fully exploited. Here, we propose a design approach to achieve tunable meta-lenses with continuous focal length manipulation working at 1550 nm based on phase-change materials (Sb2S3). The focal length can be gradually tuned from 35 to 55 μm during the conversion process between crystalline and amorphous states. The meta-atoms are rectangular shapes of different sizes and orientations to provide certain phase compensations from propagation and Pancharatnam–Berry phases, respectively. The tunable Airy beam, Bessel beam, and deflection of the meta-lens focal spot are also demonstrated to show the universality of the proposed design. This endeavor will lay the groundwork for the design of tunable meta-devices, thereby streamlining their integration into infrared systems. [ABSTRACT FROM AUTHOR]

The surface-enhanced Raman scattering (SERS) technique provides outstanding molecular fingerprint identification and high sensitivity of analytes. Herein, colloidal sphere-shaped gold nanoparticles (Au-NPs) trapped in concentric rings of the Bessel beam generated from the optical fiber-based negative axicon has been reported as a SERS substrate. With the trapping of Au-NPs, the SERS ability of colloidal Au-NPs improved, and the average enhancement factor (AEF) of the rhodamine-6G (R6G) and 4-aminothiophenol (4-ATP) molecules can reach up to the order of 107. Control experiments were also carried out with the trapping of Au-NPs by Gaussian beam illumination, without any illumination of the light and with the trapping of Au-NPs by the Bessel beam illumination on a silver (Ag)-coated silicon (Si) substrate with a self-assembled monolayer (SAM) of 4-ATP. Theoretical studies were also carried out using the finite element method (FEM) to identify the hotspots generated in the gaps formed between the Au-NPs, leading to an enhancement in the SERS signal of the molecules, and the results were consistent with the experimentally determined AEFs. The obtained results demonstrate that the proposed SERS technique is stable. This study has significant potential applications in clinical diagnosis, food safety, environment safety, chemical sensing, and biosensing. [ABSTRACT FROM AUTHOR]

This study investigates acoustic radiation forces on spherical objects generated by Bessel beams in a viscous fluid. Radiation forces on elastic spheres and shells of different materials are examined using viscid expression with the thermoviscous correction included, and the results are then compared with numerical simulations based on the finite element method. The Stokes drag force for zero-order Bessel waves was theoretically derived, and in turn, a practical example of negative radiation forces is proposed and investigated together with the gravity, the buoyancy, and the drag force from acoustic streaming. It is found that the negative pulling force exists even including the positive forces from the other sources; however, the parameter regions for pulling forces are reduced especially for small objects. This work helps the further study of particle manipulations by acoustic Bessel beams in viscous fluids and also guides the experimental realization of acoustic tractor beams. [ABSTRACT FROM AUTHOR]

Hybrid integration of solid-state quantum emitters (QEs) into nanophotonic structures opens enticing perspectives for exploiting multiple degrees of freedom of single-photon sources for on-chip quantum photonic applications. However, the state-of-the-art single-photon sources are mostly limited to two-level states or scalar vortex beams. Direct generation of high-dimensional structured single photons remains challenging, being still in its infancy. Here, we propose a general strategy to design highly entangled high-dimensional spin-orbital single-photon sources by taking full advantage of the spatial freedom to design QE-coupled composite (i.e., Moiré/multipart) metasurfaces. We demonstrate the generation of arbitrary vectorial spin-orbital photon emission in high-dimensional Hilbert spaces, mapping the generated states on hybrid-order Bloch spheres. We further realize single-photon sources of high-dimensional spin-orbital quantum emission and experimentally verify the entanglement of high-dimensional superposition states with high fidelity. We believe that the results obtained facilitate further progress in integrated solutions for the deployment of next-generation high-capacity quantum information technologies. [ABSTRACT FROM AUTHOR]

The optomechanical motion of a gold nanoparticle (GNP) dimer—a pair of optically bound GNPs—in fluid, manipulated by a Bessel beam, is theoretically studied using the multiple multipole (MMP) method. Since a Bessel beam possesses orbital angular momentum (OAM) and spin angular momentum (SAM) simultaneously, complicated rigid-body motions of the dimer can be induced. The mechanism involves the equilibrium between the optical force with the reactive drag force exerted by the fluid. Our results demonstrate that the dimer rotates around its center of mass (COM), while the COM performs an orbital revolution around the optical axis. Additionally, each individual GNP undergoes spinning. The directions of the GNPs' spin and the orbital revolution of COM depend on the handedness and the order (topological charge) of Bessel beam, respectively. Nevertheless, the rotation direction of the dimer depends on the size of GNP. In the case of a smaller dimer, the direction of dimer's rotation with respect to the COM is consistent with the handedness of the light. Conversely, a larger dimer performs a reverse rotation, accompanied by a precession during the orbital revolution. There are multiple turning points in the radius of the GNP for the alternating rotation of the dimer caused by positive or negative optical torque. Our finding may provide an insight to the optomechanical manipulation of optical vortexes on the motions of GNP clusters. [ABSTRACT FROM AUTHOR]

Large surface area applications such as high efficiency >26% solar cells require surface patterning with 1–10 μm periodic patterns at high fidelity over 1–10 cm2$1 - \left(\text{cm}\right)^{2}$ areas (before up scaling to 1 m2$ \left(\text{m}\right)^{2}$) to perform at, or exceed, the Lambertian (ray optics) limit of light trapping. Herein, a pathway is shown to high‐resolution sub‐1 μm etch mask patterning by ablation using direct femtosecond laser writing performed at room conditions (without the need for a vacuum‐based lithography approach). A Bessel beam is used to alleviate the required high surface tracking tolerance for ablation of 0.3–0.8 μm diameter holes in 40 nm alumina Al2O3$\left(\text{Al}\right)_{2} \left(\text{O}\right)_{3}$–mask at high writing speed, 7.5 cm s−1; a patterning rate 1 cm2 per 20 min. Plasma etching protocol was optimized for a zero‐mesa formation of photonic‐crystal‐trapping structures and smooth surfaces at the nanoscale level. The maximum of minority carrier recombination time of 2.9 ms was achieved after the standard wafer passivation etch; resistivity of the wafer was 3.5 Ω cm. Scaling up in area and throughput of the demonstrated approach is outlined. [ABSTRACT FROM AUTHOR]

This letter explores the possibility of long‐distance transmission of an orbital angular momentum (OAM) beam through rectangular tunnels. Theoretical analysis reveals that the OAM beam propagating in the tunnel with square cross section fulfills the conditions for axial propagation and exhibits azimuth symmetry. In comparison with free‐space OAM generation, we draw the conclusion that long‐distance transmission of OAM beams is achievable in the tunnels with square cross section. The validity of our conclusion is further substantiated through numerical experiments. Simulation results demonstrate that the first‐order OAM beam radiated by a uniform circular antenna array exhibits favorable helical phase distribution and the circular symmetry of the amplitude distribution in the tunnel beyond the Rayleigh distance. However, these characteristics degrade with increasing mode order and propagation distance, because the increase of high‐order OAM beam divergence angle and propagation distance will exacerbate the impact of multipath effects in the tunnel environment. [ABSTRACT FROM AUTHOR]

In recent years, the emergence of metasurfaces has brought revolutionary changes to the generation and processing of vortex beams, triggering widespread research interest. Meanwhile, the longitudinally varying features of propagating beams provide new design freedom for realizing multi‐dimensional optical manipulation and promote the advancements of related areas such as microscopic detection, microfabrication, and biomedical applications. In addition, self‐accelerating Bessel beams are promising for a wide range of applications such as particle manipulation and medicine due to their nondiffracting, self‐healing as well as obstacle avoidance properties. In this paper, a novel kind of curved transmitted high‐order Bessel beams with longitudinally varying features based on form‐birefringent metasurface, by simultaneously manipulating the phase profiles of output orthogonal polarization components is demonstrated. Multiple dimensions of the beam, including the propagation trajectory, polarization state, and orbital angular momentum, can be tailored arbitrarily. For verifying the feasibility of the demonstrated method, two samples with different propagation trajectories, as well as different variations of orbital angular momentum, are designed and experimentally demonstrated. Such a novel approach can open new doors for the manipulation of vortex beams and can be used for depth sensing and distance measurement in complex environments. [ABSTRACT FROM AUTHOR]

The effects of various properties on the tight focusing of light are considered. In particular, polarization of the incident field is an important consideration. Plots are presented for the variations in the focal intensity, and the area and volume of the focal spot, with numerical aperture. We consider Bessel beams, focusing with a system of circular pupil, and 4Pi focusing by a pair of opposing high-numerical-aperture lenses or a single paraboloidal mirror. [ABSTRACT FROM AUTHOR]

Achieving independent multitasked wavefront control by using an ultrathin plate is a challenge to increase information capacity in integration optics and radar applications. Transmission-reflection-integrated metasurface provides an efficient recipe primarily for multifunctional meta-device, however it is challenging to synergize both linear polarization (LP) and circular polarization (CP) using a single meta-plate. Here, a multichannel full-space coding metasurface composed of interleaved shared-aperture meta-atom is proposed to achieve large information capacity by capsulating judiciously engineered high efficiency triple sub-elements (modes) in four-layer scheme. By rotating dual-gap split ring resonator and varying size of "L" type structure insulating by a metallic ring with electrostatic-analogue shielding effect, both Pancharatnam–Berry (PB) and dynamic phases are independently realized under CP and LP waves, respectively. Such an extraordinary insulating strategy completely suppresses crosstalk among three modes and unprecedentedly increases the capability in yielding kaleidoscopic wavefront control. To verify the significance, a proof-of-concept metadevice is devised and experimentally demonstrated with tri-channel wavefront manipulations, exhibiting reflective dual-vortex beam and Bessel beam for forward and backward CP wave, respectively at high frequency, while transmissive polarization beam splitting for 45°-LP wave at low frequency. Our finding in polarization-direction multiplexing is expected to generate great interest in electromagnetic integration with emerging degree of freedoms. [ABSTRACT FROM AUTHOR]

All‐dielectric nanophotonic devices are usually fabricated by engraving arrays of nanoholes at the surface of high‐index materials, to engineer dedicated optical functions. However, their direct 3D integration in the volume of a material is challenging, inaccessible to current planar nanolithography methods. Here is introduced an ultrafast laser‐machining method that opens the possibility to realize scalable arrays of hollow nanochannels directly inside the bulk of silica glass within a single‐step, maskless, and digital approach. Using a custom‐shaped micro‐Bessel beam and by tuning laser pulse durations from femtoseconds to picosecond to boost processing versatility, dense assemblies of nanochannels with adjustable lengths (up to 30 µm), and submicron lattice periodicity (down to 0.7 µm) are achieved. As a proof‐of‐principle demonstration, a gradient‐index metaphotonic structure is realized and its performance is experimentally characterized, demonstrating its relevancy for imprinting phase functions with magnitude up to π/2$\pi /2$ in the short‐wave infrared spectral range. Results show that the unique flexibility and scalability provided by individual control of each channel opens a new realistic alternative approach for 3D fabrication of monolithic integrated nanophotonic devices inside a wide range of low‐index standard optical materials. [ABSTRACT FROM AUTHOR]

Over the past few decades, remarkable breakthroughs and progress have been achieved in ultrafast laser processing technology. Notably, the remarkable high-aspect-ratio processing capabilities of ultrafast lasers have garnered significant attention to meet the stringent performance and structural requirements of materials in specific applications. Consequently, high-aspect-ratio microstructure processing relying on nonlinear effects constitutes an indispensable aspect of this field. In the paper, we review the new features and physical mechanisms underlying ultrafast laser processing technology. It delves into the principles and research achievements of ultrafast laser-based high-aspect-ratio microstructure processing, with a particular emphasis on two pivotal technologies: filamentation processing and Bessel-like beam processing. Furthermore, the current challenges and future prospects for achieving both high precision and high aspect ratios simultaneously are discussed, aiming to provide insights and directions for the further advancement of high-aspect-ratio processing. [ABSTRACT FROM AUTHOR]

The model given by Patil et al., for the self-focusing of lowest-order Bessel–Gaussian laser beam, is revisited by introducing the exponential plasma density ramp in this paper. Plasma density changes due to combined effect of the relativistic and ponderomotive nonlinearities, which arise due to the nonuniform spatial profile of the laser beam leading to stronger self-focusing. Under paraxial ray approximation, the expression for the evolution of laser-beam width parameter is obtained and solved numerically in order to achieve self-focusing. We have observed that as Bessel beam propagates through the plasma, it does not diffract and spread out, which is in contrast to the usual behavior of light that spreads out after being focused down to the small spot. Laser spot size decreases considerably under the presence of exponential density ramp. This study will be useful for better understanding the self-focusing mechanism of lasers as it becomes effective for the optimized parameters under the proposed situation. Bessel laser beams play an important role in enhancing the energy gain in laser-driven accelerators. In addition, for all laser-driven plasma-based accelerators, it appears possible to guide a laser beam over large distances using a plasma density channel, thus enhancing the acceleration length and the energy gain. [ABSTRACT FROM AUTHOR]

This editorial discusses the advancements in laser fabrication technologies and their diverse applications. The field of laser fabrication has evolved from basic light sources to sophisticated tools, such as ultrafast femtosecond lasers, which enable precise manufacturing. The editorial summarizes 14 papers that highlight the optimization of laser fabrication techniques, the processing of various materials, the fabrication of micro-/nanostructures, and customized applications. The articles cover topics such as optimizing laser parameters, improving material properties, creating micro- and nanostructures, and applications in ophthalmic surgery and anti-reflection surfaces. These advancements have the potential to address challenges in various industries and improve clinical outcomes. [Extracted from the article]

Fused silica with surface structures has potential applications in microfluidic, aerospace and other fields. To fabricate structures with high dimensional accuracy and surface quality is of paramount importance. However, it is indeed a challenge to strike a balance between accuracy and efficiency at the same time. Here, a temporally shaped femtosecond laser Bessel-beam-assisted etching method with dual-control of incubation effect is proposed to achieve this balance. Instead of layer-by-layer ablation continuously with Gaussian pulses, silica is modified discretely by double pulse Bessel beam with one single layer. During the modification process, incubation effect is dual-controlled in single shot process and spatial scanning process to generate even modified region efficiently. Then, the modified region is etched to form designed structures such as microholes, grooves, etc. The proposed method exhibits high efficiency for fabrication of surface structures in fused silica. [ABSTRACT FROM AUTHOR]

In this study, we fabricated laser-induced periodic surface structures (LIPSS) on a germanium surface through laser ablation in air using axicon and femtosecond (fs) pulses. This novel approach permitted the nanoscale material processing outcome refinement via an fs Bessel beam. Our investigations aimed at systematically understanding the formation of periodic structures under various experimental conditions, such as (i) different pulse energies ranging from 50 µ J to 1000 µ J at a constant scan speed and (ii) constant energy with different scan speeds (0.1–3 mm s−1). By adjusting the fluences and scan speeds, we were able to identify the parametric space and alter the periodicity of the low-spatial frequency LIPSS and high-spatial frequency LIPSS on germanium, which were analyzed using field emission scanning electron microscopy. An optimal LIPSS formation over a large area of germanium was achieved at an input energy of 250 µ J and a scan speed of 0.75 mm s−1. Additionally, we measured the contact angles of the Ge nanostructures (GeNSs) to demonstrate their hydrophobic nature and non-wetting properties, providing insights into the behavior of LIPSS. Subsequently, the GeNSs were coated with a ∼15 nm thick gold (Au) film using a thermal deposition method. Utilizing these, the surface-enhanced Raman spectroscopy (SERS) technique detected diverse analytes, such as tetryl (an explosive) at a concentration of 50 µ M and thiram (a pesticide) at 500 nM. The SERS enhancement factors for tetryl and thiram molecules on GeNSs coated with a 15 nm-thick Au layer were determined to be 2.5 × 104 and 4.2 × 105, respectively. [ABSTRACT FROM AUTHOR]

For the application of vortex electromagnetic (EM) beams in practical detection scenes, the scattering characteristics of electrically large arbitrarily shaped targets illuminated by an off-axis Laguerre–Gaussian (LG) vortex beam are investigated and compared to the on-axis incidence case. The vector potential method is used to extract the electric and magnetic field components of the LG beam in different polarization states. The physical optics algorithm is adopted to calculate the scattering fields of four typical targets with the shape of a sphere, NASA almond, blunt cone, and blade model. The results revealed that as the beam center offset and the topological charge of the incident vortex beam increase, the scattering field distorts, and the obvious orbital angular momentum (OAM) spectrum mixing occurs. In addition, OAM spectrum aliasing occurs for asymmetric targets, even at on-axis incidence. These results elucidate the mechanism of vortex EM scattering and provide a reference for applying vortex beams for target detection and recognition. [ABSTRACT FROM AUTHOR]

Sub-terahertz communications (100–300 GHz) are explored today as a candidate technology to enable extremely high-rate, low-latency data services and high-resolution sensing in beyond-fifth-generation (beyond-5G) wireless networks. However, these sub-terahertz wireless systems will often have to operate in the near field, where the signal propagation does not follow canonical far-field models, including the commonly used free space path loss equation. Instead, the signal propagation in the near field follows more complex patterns that are not well-captured with analytical far-field models standardized for 5G research. Moreover, state-of-the-art beamforming solutions exploited heavily in fourth-generation (4G) and 5G networks are notably less efficient in the near field. In this article, the near-field sub-terahertz channel is accurately measured and analyzed. In addition to state-of-the-art beamforming, the article also analyzes the sub-terahertz channel measurements when using near-field-specific Bessel beams that demonstrate fewer power fluctuations in the near field in addition to higher focusing gain. Novel distance-centric and angle-centric dependencies reported in this article may serve as a reference when developing next-generation channel models for sixth-generation (6G) and beyond-6G near-field sub-terahertz wireless systems. [ABSTRACT FROM AUTHOR]

Exploring and taming the diffraction phenomena and divergence of light are foundational to enhancing comprehension of nature and developing photonic technologies. Despite the numerous types of nondiffraction beam generation technologies, the 3D deformation and intricate wavefront shaping of structures during propagation have yet to be studied through the lens of nanophotonic devices. Herein, the dynamic conversion of a circular Airy beam (CAB) to a Bessel beam with a single‐layer spin‐selective metasurface is demonstrated. This spatial transformation arises from the interplay of 1D local and 2D global phases, facilitating the 3D control of non‐diffractive light fields. An additional overall phase gradient and orbital angular momentum are introduced, which effectively altering the propagation direction and transverse fields of complex amplitude beams along the optical path. The manifested samples exhibit superior defect resistance, laying a crucial application in micro/nanolithography technologies. This approach expands the in‐plane spin‐selective mechanism and leverages the out‐of‐plane propagation dimension, allowing for integrated high‐resolution imaging, on‐chip optical micromanipulation, and micro/nanofabrication within a versatile nanophotonic platform. [ABSTRACT FROM AUTHOR]

The selective control and manipulation of nanoparticles require developing and researching new methods for designing optical tweeters, mainly based on a photonic hooks (PHs) effect. This paper first proposes a tunable PH in which a structured beam illuminates an anisotropic cutting liquid crystal microcylinder based on the Finite-DifferenceTime-Domain (FDTD) method. The PHs generated by plane wave, Gaussian, and Bessel beam are analyzed and compared. The impact of beams and LC particle parameters on the PHs are discussed. Where the influence of the extraordinary refractive index ( n e ) on PHs is emphasized. Our results reveal that introducing birefringence can change the bending direction of PH. Besides, the maximum intensity of the PHs increases as n e increases regardless of the beam type. The PH generated by a plane wave has a higher maximum intensity and smaller FWHM than that generated by the Gaussian and Bessel beams. The smallest FWHM and maximum intensity of the PHs generated by the Gaussian falls between that generated by the plane wave and the Bessel beam. The PH generated by a Bessel beam has the minor maximum intensity and the largest FWHM. Still, it exceeds the diffraction limit and exhibits bending twice due to its self-recovery property. This paper provides a new way to modulate PH. This work offers novel theoretical models and the degree of freedom for the design of PHs, which is beneficial for the selective manipulation of nanoparticles. It has promising applications in Mesotronics and biomedicine. [ABSTRACT FROM AUTHOR]

Synchronous laser beam scanning is a common technique used in single-photon imaging where the spatial resolution is primarily determined by the beam divergence angle. In this context, Bessel beams have been investigated as they can overcome the diffraction limit associated with traditional Gaussian beams. Notably, the central spot of a Bessel beam retains its size almost unchanged within a non-diffractive distance. However, the presence of sidelobes in the Bessel beam can negatively impact spatial resolution. To address this challenge, we have developed a single-photon imaging system with high-depth resolution, which allows for the suppression of echo photons from the sidelobe light in the depth image, particularly when their flight time differs from that of the central spot. In our LiDAR setup, we successfully achieved high-resolution scanning imaging with a spatial resolution of approximately 0.5 mm while also demonstrating a high-depth resolution of 12 mm. [ABSTRACT FROM AUTHOR]

The transformation regulation of the radial finite Airy-Gaussian beam array (FAiGBA) in uniaxial crystals orthogonal to the optical axis has been explored analytically and numerically under the paraxial approximation. The analytical evolution solution of this beam array in the x- and y-directions has been derived, respectively. The intensity distribution and side view of FAiGBA propagating in three types of uniaxial crystals have been demonstrated in several instances. Furthermore, particular attention has been devoted to the linear effect when this beam array transmits through the electro-optic crystal. The influence of non-paraxial longitudinal component and temperature on FAiGBA evolution characteristics has also been examined to verify the validity of the paraxial mechanism of this beam array propagating in uniaxial crystals. It is anticipated that these research findings will contribute to the advancement of FAiGBA applications in micro- and nano-control, optical fiber communication, optical trapping, and manipulation fields. [ABSTRACT FROM AUTHOR]

Due to the powerful capability in manipulating electromagnetic (EM) waves, digital coding and programmable metasurfaces have found vast application prospects across numerous areas such as next‐generation wireless communications and digital holography. Liquid crystals (LCs), as dielectric materials with significant birefringence effect over a wide frequency range, provide a cost‐effective solution for achieving the programmable metasurfaces and flexible EM manipulations, especially in the terahertz (THz) band. Different from the conventional 1D control and single functionality of transmissive LC‐based devices, here, a 16 × 16 addressable amplitude‐phase coding meta‐device is proposed to support for frequency multiplexing by using the film on glass (FOG) technology. Both numerical simulations and experimental results demonstrate that the meta‐atom exhibits an amplitude modulation depth over 90% and a phase tuning range ≈180° at two distinct frequencies, and hence the single meta‐device can provide multifunctional EM applications, including near‐field printing imaging, 3D THz energy convergence, and zero‐order Bessel beam generation. The proposed strategy paves a way for constructing highly integrated and high‐performance THz multifunctional information processing systems. [ABSTRACT FROM AUTHOR]

As a vector version of scalar Bessel beams, Poincaré–Bessel beams (PBBs) have attracted a great deal of attention due to their non-diffracting and self-healing properties as well as the presence of polarization singularities. Previous studies of PBBs have focused on cases that consist of a superposition of Bessel beams in orthogonal circular polarization states; here, we present a theoretical and experimental study of PBBs for which the polarization states are taken to be linear, which we call a linear PBB. Using a mode transformation of a full Poincaré beam constructed from linear polarization states, we observe the linear PBB as providing an in-principle infinite number of covers of the Poincaré sphere in the transverse plane and with an infinite number of C-points with positive and negative topological indices. We also study the dynamics of C-point singularities in a linear PBB in the process of self-healing after being obstructed by an obstacle, providing insight into "Hilbert Hotel" style evolution of singularities in light beams. The present study can be useful for imaging in the presence of depolarizing surroundings, studying turbulent atmospheric channels, and exploring the rich mathematical concepts of transfinite numbers. [ABSTRACT FROM AUTHOR]

The improved absolute nodal coordinate formulation (D-H-ANCF) is proposed for analyzing dynamic behaviors of the variable cross-section beam with large aspect ratio. The higher-order ANCF (H-ANCF) is established by introducing higher-order freedom degrees. Then the reduction factors of each element are proposed by considering the aspect ratio criterion and shear performance criterion. The experiments are studied to verify the correctness of the proposed method. In conclusion, shear locking can be solved by D-H-ANCF. And the deformation and cross-section distortion also can be accurately predicted by D-H-ANCF. Moreover, the computing efficiency of D-H-ANCF can be improved by introducing reduction factors. [ABSTRACT FROM AUTHOR]

A nondiffracting propagation of an optical beam through a four-level double-V-type quantum system near a plasmonic nanostructure is investigated. We study the linear absorption and dispersion properties of the quantum system as it interacts with two laser fields. We discuss the effect of the control beam with a Laguerre-Gaussian (LG) profile on the focusing of the probe beam in the presence of a plasmonic nanostructure. An appropriately selected control beam excites one transition of the atomic system and generates a spatially varying refraction index modulation for a weak probe beam that couples to the other transition. We demonstrate that placing a plasmonic nanostructure at a nanometer distance from the atomic system and using a control field with the spatial structure leads to the diffraction-less propagation of the probe beam through the atomic system. Also, it is shown that the optical properties and probe beam focusing can be controlled by adjusting the distance of the plasmonic nanostructure from the atomic system. The proposed all-optical waveguide with high contrast and transmission can be used to implement applications such as image transfer through the medium and image processing. [ABSTRACT FROM AUTHOR]

In this study, the instability and bifurcation diagrams of a functionally graded (FG) porous sandwich beam on an elastic, viscous foundation which is influenced by an axial load, are investigated with an analytical attitude. To do so, the Timoshenko beam theory is utilized to take the shear deformations into account, and the nonlinear Von-Karman approach is adopted to acquire the equations of motion. Then, to turn the partial differential equations (PDEs) into ordinary differential equations (ODEs) in the case of equations of motion, the method of Galerkin is employed, followed by the multiple time scale method to solve the resulting equations. The impact of parameters affecting the response of the beam, including the porosity distribution, porosity coefficient, temperature increments, slenderness, thickness, and damping ratios, are explicitly discussed. It is found that the parameters mentioned above affect the bifurcation points and instability of the sandwich porous beams, some of which, including the effect of temperature and porosity distribution, are less noticeable. [ABSTRACT FROM AUTHOR]

In light of the certainty of size effect on heat conduction process in extremely small dimensions, the present article seeks to introduce a new theoretical framework for thermoelastic damping (TED) in micro-/nanobeam resonators with circular cross section by utilizing the non-Fourier model of nonlocal dual-phase-lag (NDPL). The first stage involves using NDPL model in order to develop the non-Fourier heat equation of circular cross-sectional beams in polar coordinates. This differential equation can be solved to arrive at temperature distribution in any arbitrary point of the beam. When the constitutive equations of the beam together with the extracted temperature distribution are substituted in the energy-based formulation of TED, an infinite series is produced as the TED relation in the context of NDPL model. Through a comparison study, the reliability of the acquired formula is analyzed. To shed light on how some key factors like nonclassical parameters of NDPL model, beam dimensions and material affect TED, several numerical data are prepared. As per the acquired outcomes, notably at high frequencies of oscillation, the use of NDPL model may profoundly impact the quantity and pattern of TED. [ABSTRACT FROM AUTHOR]

In this article, we derive the equations that constitute the mathematical model of extensible thermoelastic beam in the context of second sound model which turns to the Gurtin–Pipkin's one. These nonlinear governing equations are derived according to the von Kármán theory and simplified by the Euler–Bernoulli approximation in the context of Gurtin–Pipkin's law. Even more so, the case of Fourier's law can be recovered from the derived system one through a proper singular limit procedure, where the memory kernel collapses into the Dirac mass at zero. Then, we show that the Gurtin–Pipkin's derived model is globally well-posed using the semigroup theory and the corresponding solutions decay exponentially under a condition on physical coefficients of the model. Finally, by an approach based on the Gearhart–Herbst–Prüss–Huang theorem, we prove that the linear (without extensibility) associated semigroup is not analytic. Finally, we show that Cattaneo's law is a particular example of Gurtin–Pipkin's law for suitable choice of the memory kernel. [ABSTRACT FROM AUTHOR]

In this paper, evolution properties of a generalized Hermite cosh-Gaussian (GHchG) beam propagating through a chiral medium are investigated. By using the Huygens–Fresnel integral formula, analytical expression of a GHchG beam in a chiral medium is obtained. We numerically simulate the corresponding beam under both chiral and beam parameters. By controlling these parameters, we can exhibit the GHchG beam in many different intensity modes. Results demonstrate that the chiral factor of the medium and the source beam parameters during beam propagation affect the spatial properties of the GHchG beam in the chiral medium. The results of this work could be shown the helpfulness in understanding the interaction between the GHchG beam and a chiral medium. [ABSTRACT FROM AUTHOR]

• A coupling dynamic model of the non-symmetric spatial dumbbell-type system is developed. • A structure-preserving numerical iteration method is proposed to solve the coupling problems concerned. • The effects of the masses of additional particles on orbit-attitude-vibration coupling behaviors of the model are revealed. The structural symmetric breaking of the spatial structure will enhance the coupling dynamic behaviors and bring new challenges for the dynamic analysis on the spatial structure inevitably. The main contribution of this paper is proposing a structure-preserving iteration method to investigate the effects of the dynamic symmetry-breaking factors on the dynamic behaviors of the rigid-flexible coupling systems. Firstly, the spatial flexible damping beam assembled with two particles on both ends is simplified as an asymmetric spatial dumbbell-type model. For this model, the coupling dynamic equations are presented based on the Hamiltonian variational principle. Then, connecting the symplectic precise integration method for the ordinary differential equations mainly controlling the plane motion of the model and the generalized multi-symplectic scheme for the partial differential equation mainly controlling the transverse vibration of the beam, a structure-preserving numerical iteration method is proposed, which provides a new way to analysis the dynamic behaviors of the coupling problems with the symmetric breaking. Finally, the effects of the absolute mass and the mass ratio of the additional particles on the orbit radius, the orbit true anomaly velocity, the attitude angle velocity of the model and the transverse vibration of the flexible beam are reproduced by using the structure-preserving numerical iteration method in the numerical simulations. Particularly, the effects of the additional particles on the attitude stability of the model and the vibration dissipation of the flexible damping beam are investigated, which gives some guidance for the attitude adjustment strategy and the vibration control method for the spatial flexible structure with the structural symmetric breaking. [ABSTRACT FROM AUTHOR]

Microrheology, the study of material flow at micron scales, has advanced significantly since Robert Brown's discovery of Brownian motion in 1827. Mason and Weitz's seminal work in 1995 established the foundation for microrheology techniques, enabling the measurement of viscoelastic properties of complex fluids using light-scattering particles. However, existing techniques face limitations in exploring very slow dynamics, crucial for understanding biological systems. Here, we present a proof of concept for a novel microrheology technique called "Optical Halo", which utilises a ring-shaped Bessel beam created by optical tweezers to overcome existing limitations. Through numerical simulations and theoretical analysis, we demonstrate the efficacy of the Optical Halo in probing viscoelastic properties across a wide frequency range, including low-frequency regimes inaccessible to conventional methods. This innovative approach holds promise for elucidating the mechanical behaviour of complex biological fluids. [ABSTRACT FROM AUTHOR]

The cutting of thick glass is extensively employed in aerospace, optical, and other fields. Although ultrafast laser Bessel beams are heavily used for glass cutting, the cutting thickness and cutting quality need to be further improved. In this research, the high-quality cutting of thick glass was realized for the first time using ultrafast laser perforation assisted by CO2 laser separation. Initially, an infrared picosecond laser Bessel beam was employed to ablate the soda-lime glass and generate a perforated structure. Subsequently, a CO2 laser was employed to induce crack propagation along the path of the perforated structure, resulting in the separation of the glass. This study investigates the influence of hole spacing, pulse energy, and the defocusing distance of the picosecond laser Bessel beam on the average surface roughness of the glass sample cutting surface. The optimal combination of cutting parameters for 6 mm thick glass results in a minimum surface roughness of 343 nm in the cross-section. [ABSTRACT FROM AUTHOR]

Recently, full Poincaré beams (FPBs) with spatially variant polarization states spanning the entire surface of the Poincaré sphere have attracted considerable interests. Expanding the FPBs into an array way has the promising applications from multiparticle manipulation to optical communication. However, how to efficiently generate a high‐purity FPB array with intracavity method remains elusive. Here, a metasurface‐integrated degenerate cavity laser is proposed for efficient generation of 10 × 10 FPB array, where a pair of metasurfaces are adopted to independently modulate the circular polarization state while compensating the mode discrepancies within the cavity. Such a design strategy enables a self‐reproducing intracavity optical field, concurrently ensuring the stabilization of intracavity oscillation. It is numerically demonstrated that the purity of orbital angular momentum (OAM) in the first‐order FPB array can approach to 92.89%, with a root‐mean‐square error (RMSE) of polarization ellipse parameters below 8.17%. This work provides a compact and efficient design platform for the generation of a variety of vector beam arrays and may find promising applications in free space communication and multiple particle manipulation. [ABSTRACT FROM AUTHOR]

Medical accelerators have been widely used in tumor radiation therapy. Accurate isocenter coincidence between treatment beams and imaging systems is critical for image-guided radiation therapy (IGRT). We propose a method utilizing a phantom with marker spheres to detect the Nine Degrees of Freedom (9-DOF) in the system's geometric model to assess isocenter coincidence between the treatment beams and the kV cone-beam computed tomography (CBCT). The phantom was initially aligned with the accelerator. Subsequently, the projections of the treatment and CBCT beams' were acquired separately with full gantry rotation. By analyzing the marker spheres' position in both the treatment beam and CBCT beam projections, the 9-DOF parameters were calculated. A comparison with a Winston-Lutz-based system was performed. Then, the analysis revealed imprecise circular trajectories with noticeable random deviations in the rotations of both the treatment beams and CBCT. The isocenter deviations for the treatment beams and CBCTwere 0.18 mm (X), -0.49 mm (Y), and -0.35 mm (Z) after trajectories fitting, respectively. The rotational planes of the two systems exhibited a pinch angle of 0.0235°. This proposed method offers a quantitative assessment of the geometric pose of the source and the detector panel, and the isocenter coincidence of the treatment beams and imaging systems of an accelerator at each gantry angle. [ABSTRACT FROM AUTHOR]

A 3D transmitarray (TA) is proposed to generate dual-polarized orbital angular momentum (OAM) beams with gain and mode purity filtering responses. The TA units are realized by square cavity filters with the same passband and different orders and inner widths, resulting in different coupling cavity numbers. The evanescent modes in the coupling cavities will greatly decrease the propagation constant, thus generating a large phase variation. The square structure of the cavity filter makes it able to support dual-polarized wave propagation with the same phase delay and insert loss. Based on these transmission characteristics, eight different TA units are designed to realize a 3-bit phase gradient within the passband of 25.4–26.7 GHz. It should be emphasized that the dispersed transmission phase and magnitude of the eight TA units in the stopbands will deteriorate the purity of the OAM beam. Therefore, the gain and mode purity filtering responses can be realized simultaneously. In order to verify the performance of the proposed OAM TA design, a TA prototype with the mode number l = −1 is fabricated by 3D printing technology. The TA can realize the maximum gain of 25.9 dB in the passband, and the rejection level is below −15.0 dB within the main beam direction. The purities of dual-polarized OAM beams are over 0.5 in the passband, and the cross-polarization is below −16.5 dB. The advantages of the OAM TA, including gain-filtering and mode purity-filtering responses, dual-polarization, and high efficiency make it a promising solution for millimeter-wave OAM sensing and communication applications. [ABSTRACT FROM AUTHOR]

The ionosphere can be artificially modified by employing ground-based high-power high-frequency electromagnetic waves to irradiate the ionosphere. This modification is achieved through the nonlinear interaction between the electromagnetic waves and the ionospheric plasma, leading to changes in the physical properties and structure of the ionosphere. The degree of artificial modification of the ionosphere is closely related to the heating energy density of high-frequency pump waves. Due to the high density of neutral constituents in the lower ionosphere and the high frequency of electron-neutral collisions, the energy of heating pump waves will be absorbed and attenuated during the penetration of the low ionosphere, seriously affecting the heating effect. This paper proposes a method to reduce the absorption of ionospheric heating pump waves by releasing electron attachment chemicals into low ionosphere to form a large-scale electron density hole. A model for mitigating pump waves absorption based on SF6 release is established, and the absorption at different frequencies is quantitatively calculated. The propagation characteristics of high-frequency signals in ionospheric holes are studied using a three-dimensional ray tracing method, and the results demonstrate that the chemical release method not only reduces the absorption attenuation of heating pump waves but also forms spherical electron density holes, which exhibit a focusing effect on the heating beam and enhance the heating effect. The results are of great significance for understanding the nonlinear interaction between electromagnetic wave and ionospheric plasma and improving the ionospheric heating efficiency. [ABSTRACT FROM AUTHOR]

Hollow beam is a peculiar structure beam, which has been widely used in various areas. Here, we propose a novel diffraction optical element to generate tunable hollow beams. This element is composed of periodic concentric rings. The phase of each ring is periodically distributed between -n and n and satisfies a complex variable function. By tuning the parameters of the structure, we can flexibly manipulate the size and length of the hollow beam. The length of the beam can be increased from 98 X to 248 X, and the full width at half maximum varies from 0.43 X to 0.61 X. Moreover, the light intensity and side lobe of the hollow beam can also be regulated using the designed diffraction optical element. The potential applications of this highly tunable hollow beam include optical nanomanipulation, microscopic imaging, and nanolithography. [ABSTRACT FROM AUTHOR]

Laser wake field acceleration (LWFA) is limited by some determinative aspects, such as wave breaking, dephasing, pulse divergence, etc. One of the proposed methods to overcome the acceleration limitations of the LWFA is spatio-temporal controlling of the laser focus, named flying focus. In this article, flying focus dynamics for two Bessel beam profiles is derived with complex source point method (CSPM). We investigate the two pulse with basic Gaussian and Donut-like profiles, those focal points move at a speed very close to the speed of light. Our selected flying focus parameters maintain laser intensity up to 16 times the Rayleigh length (− 8ZR, + 8ZR). We also examined the flying focus LWFA (FF-LWFA) energy gain and trapping rate for these two cases. Numerical results show that accelerated electron bunch is converged considerably for the Donut shape profile. This convergence is due to the inward radial ponderomotive force, and furthermore suitable phase difference between longitudinal and transverse wake field components. Since electrons are hold near the axis for a longer distance and keep more energy from the wake. In average 2.8% of the injected electrons are accelerated up to 255 MeV for the donut-like profiles, while only 1.4% of electrons are accelerated up to 155 MeV for Gaussian profile. [ABSTRACT FROM AUTHOR]

Dynamics modeling and analysis of a rotating piezoelectric laminated beam (RPLB) considering the effect of the setting angle is presented in this paper. The rotating piezoelectric energy harvester can be simplified as a RPLB which is fixed at a rotating hub. It is easy to know that a steady transversal deformation would be produced due to the transversal component of centrifugal force when the beam is not along the radial direction (the setting angle is not equal to 0° or 180°). However, the variation of steady transversal deformation and its effect were rarely considered by existing theoretical models about the rotating harvesters. To this end, a novel nonlinear dynamics model of the RPLB is developed by the combination of floating frame reference (FFR) and absolute nodal coordinate formulation. In the model, the position coordinates and gradients on the FFR are used as the nodal coordinates to describe deformation field. The enthalpy, elastic and kinetic energies of the RPLB are derived with consideration of the piezoelectric constitutive equation and the rotation of the FFR. Thus, the dynamics equations of the RPLB can be developed by using the Lagrange's equations of second kind. The results obtained from the model show agreement with those obtained from the previous literatures, which verifies the correctness of the model. Several examples are presented to analyze the effects of rotating speed, setting angle and tip mass on steady transversal deformation, output voltage and modal characteristics. • A novel nonlinear dynamics model of RPLB is developed to benefit the design of piezoelectric energy harvesters. • Steady deformation caused by transversal component of centrifugal force and its effects are investigated and analyzed. • Variations of the dynamic stiffening / softening of RPLB with setting angle and its reason are discussed. • Tensile strains and compression strains respectively lead to dynamic stiffening and softening. [ABSTRACT FROM AUTHOR]

The analytical expression of the axial acoustic radiation force (ARF) exerted on a spherical particle located on the propagation axis of non-diffracting beams constructed by a discrete superposition of Bessel beams is calculated. The axial acoustic radiation for the fundamental non-diffracting beams as cosine beams, Bessel beams, Mathieu beams, and parabolic or Weber beams are considered. In this study, we extend the recent results on the ARF concerning Bessel and Mathieu beams to include the other fundamental non-diffracting cosine and parabolic beams. Additionally, the influences of each beam parameter, such as the angle of the half cone, the beam's own value, and the beam order on ARF will be examined, and the dependence of ARF with the particle radius is treated. In addition, some numerical simulations are performed the influence these parameters on the ARF. Furthermore, a comparison between the ARF exerted by each non-diffracting beam is accomplished by analyzing the curves of the dimensionless force function Yp versus the size parameter ka. This work may contribute to understanding the interaction between spherical particles and the fundamental non-diffracting beams. [ABSTRACT FROM AUTHOR]

The study of a Gaussian laser beam interacting with an optical prism, both through reflection and transmission, provides a technical tool to examine deviations from the optical path as dictated by geometric optics principles. These deviations encompass alterations in the reflection and refraction angles, as predicted by the reflection and Snell laws, along with lateral displacements in the case of total internal reflection. The analysis of the angular distributions of both the reflected and transmitted beams allows us to understand the underlying causes of these deviations and displacements, and it aids in formulating analytic expressions that are capable of characterizing these optical phenomena. The study also extends to the examination of transverse symmetry breaking, which is a phenomenon observed in the laser beam as it traverses the oblique interface of the prism. It is essential to underscore that this analytical overview does not strive to function as an exhaustive literature review of these optical phenomena. Instead, its primary objective is to provide a comprehensive and self-referential treatment, as well as give universal analytical formulas intended to facilitate experimental validations or applications in various technological contexts. [ABSTRACT FROM AUTHOR]

In this paper, the coherent properties of partially coherent Bessel–Gaussian optical beams propagating through a uniform medium (free space) or a turbulent atmosphere are examined theoretically. The consideration is based on the analytical solution of the equation for the transverse second-order mutual coherence function of the field of partially coherent optical radiation in a turbulent atmosphere. For the partially coherent Bessel–Gaussian beam, the second-order mutual coherence function of the source field is taken as a Gaussian–Schell model. In this approximation, we analyze the behavior of the coherence degree and the integral coherence scale of these beams as a function of the propagation pathlength, propagation conditions, and beam parameters, such as the radius of the Gauss factor of the beam, parameter of the Bessel factor of the beam, topological charge, and correlation width of the source field of partially coherent radiation. It was found that, as a partially coherent vortex Bessel–Gaussian beam propagates through a turbulent atmosphere, there appear not two (as might be expected: one due to atmospheric turbulence and another due to the partial coherence of the source field), but only one ring dislocation of the coherence degree (due to the simultaneous effect of both these factors on the optical radiation). In addition, it is shown that the dislocation of the coherence degree that significantly affects the beam coherence level is formed only for beams, for which the coherence width of the source field is larger than the diameter of the first Fresnel zone. [ABSTRACT FROM AUTHOR]

This document is a collection of research papers and a review article on the topic of non-diffractive beams, specifically Bessel beams, and their applications in various fields. The papers cover a range of topics, including the propagation properties of circular airy vortex beams, optical force and torque on graphene-coated gold nanospheres, generation of complex transverse energy flow distributions, and micro-hole generation using high-energy pulsed Bessel beams. The review article provides an overview of non-diffractive Bessel beams in ophthalmology and their advantages and disadvantages compared to existing systems. The document aims to provide library patrons with a comprehensive understanding of non-diffractive beams and their potential applications in fields such as microscopy, optical trapping, precision laser machining, medical imaging, quantum optics, and optical communication. [Extracted from the article]

Acoustic manipulation using surface acoustic wave has aroused widespread interest in life sciences, biomedical, and bioanalytical chemistry. Acoustic manipulation for different applications requires different acoustic fields. Bessel beams are non-diffractive and re-constructable, bringing possibility and versatility of acoustic manipulation integrated on microfluidic chips. To date, there are a few studies on constructing Bessel surface acoustic waves. Moreover, there is still a lack of dynamic acoustic manipulation using Bessel surface acoustic waves propagating along a surface of piezoelectric substrate with simple and high-precision devices. Here, we design a device with two omnidirectional equifrequency interdigital transducers to form a quasi-Bessel surface acoustic wave by means of coherent interference. The proposed device avoids influences of anisotropy on its operating frequency, making its quasi-Bessel beam accurately and stably conform to the predetermined design acoustic field. This acoustic field could control micrometer to submicrometer particles and dynamically move particles along lateral direction and axial direction of the propagation of quasi-Bessel beam. A phenomenon similar to negative force appeared when the two-micron spherical particles were manipulated. The quasi-Bessel beam formed by our device can provide a versatile movement for on-chip acoustic manipulation. [ABSTRACT FROM AUTHOR]

Vibration-based condition monitoring for remotely located rotating blades is one of the important aspects to avoid sudden breakdown of the machinery. Vibration analysis of damaged blades provides the information to identify the damage during operation. In this work, dynamic attributes of rotating cracked tapered cantilever functionally graded material (FGM) beams for various tapered configurations are investigated using energy method. The nonlinearity due to in plane stretching as a result of large deformations is taken in to consideration. Nonlinear governing equations for cracked rotating tapered FGM beams are generated by optimizing the energy functional. An iterative algorithm is developed to solve the derived nonlinear equations. The effects corresponding to location of crack and centrifugal stiffening on the various modes has been presented for different tapered configurations, material indices, crack depths and rotational speeds. Crack compensating speeds are studied and reported for different tapered ratios and crack parameters for the first time. The effect of crack location and crack depth on the first two nonlinear frequency ratios is also investigated for different tapered configurations and material indices. The influence of centrifugal stiffening on nonlinear responses of FGM beams is presented for various crack parameters and tapered configurations. [ABSTRACT FROM AUTHOR]

Based on the existing permanent load equilibrium method, influence matrix method and adaptive control method, a distributed algorithm and control method for the cable forces of hybrid laminated girder cable-stayed bridges is proposed. The method uses the permanent load equilibrium approach to initially determine the permanent load cable forces, then adjusts it based on the influence matrix of the main girder displacement, and finally combines the calculation of finite element software to determine the cable forces that satisfy the internal force requirements of each member of the hybrid laminated girder cable-stayed bridge under the joint action of permanent load and live load. Through adjusting the cable force of an actual bridge, it can be found that this method is highly efficient in calculation, and the efficiency and accuracy of control of the cable forces are high, ensuring that the cable forces and alignment of the bridge structure after completion are in line with the design expectations. [ABSTRACT FROM AUTHOR]

The art of light engineering unveils a world of possibilities through the meticulous manipulation of photonic properties such as intensity, phase, and polarization. Precision control over these properties finds application in a variety of fields spanning communications, light–matter interactions, laser direct writing, and imaging. Terahertz (THz) range, nestled between microwaves and infrared light, stands out for its remarkable ability to propagate with minimal losses in numerous dielectric materials and compounds, making THz imaging a powerful tool for noninvasive control and inspection. In this study, a rational framework for the design and optimal assembly of nonparaxial THz imaging systems is established. The research is centered on lensless photonic systems composed solely of high‐resistivity silicon‐based nonparaxial elements such as the Fresnel zone plate, the Fibonacci lens, the Bessel axicon, and the Airy zone plate, all fabricated using laser ablation technology. Through a comprehensive examination through illumination engineering and scattered light collection from raster‐scanned samples in a single‐pixel detector scheme, the imaging systems are evaluated via diverse metrics including contrast, resolution, depth of field, and focus. These findings chart an exciting course toward the development of compact and user‐friendly THz imaging systems where sensors and optical elements seamlessly integrate into a single chip. [ABSTRACT FROM AUTHOR]