Trapping two types of particles by modified circular Airy beams

Adjustable focusing property of circular Airyprime beam through Fourier space modulation

Airyprime beams are known for their powerful autofocusing property, which are further enhanced by the introduction of a circular structure-circular Airyprime beam (CAPB). We derive an asymptotic expression of the CAPB in Fourier space (FS) and verify its accuracy by the numerical Fourier transform (FT) method. Through FS modulation on it, adjustable control of autofocusing property of the FS-modulated CAPB can be achieved, whose lower and upper limits can reach 8.7% reduction and 2.6 times enhancement compared to the unmodulated one. The experimental results agree well with the numerical analyses. Our findings offer promising possibilities for efficient particle trapping and enhancing free-space optical communication capabilities.

Abrupt autofocusing beam from a phase-only mask

Airy beams have become an important beam shape for structured light beams because of their interesting self-accelerating and parabolic propagation properties. Many variants of Airy beams have been proposed, among which the Airy beam with cylindrical symmetry [also known as the circular Airy beam or abrupt autofocusing (AAF) beam] is particularly peculiar and has attracted special attention due to its shape transformation during propagation. Much effort has been devoted to understanding the properties of the AAF beam. In this work, we present simulation results for generating the AAF beam using a phase-only mask. A cubic chirp-modulated axicon phase is used to create the mask. We found an optimal value for the axiconic phase, and the cubic phase is essential for controlling the AAF beam's shape. We demonstrate that a phase-only mask is an effective and simple method for generating high contrast between the initial and AAF plane. We present the results for beam formation and propagation dynamics of the AAF beam using the control parameters of the phase mask. We also discuss the design parameters and their influence on the AAF beam shapes. Our results pave the way for a deeper understanding of the beam formation and propagation dynamics of the AAF beam.

Needle of longitudinally polarized light using the circular Airy beam

An optical needle is created using a radially polarized circular Airy beam with a conical angle, stemmed from the auto-focusing property of light beams. The utilization of the angular spectrum representation serves to illustrate the field distributions of the optical needle, and an explicit formula is provided to describe the angular spectrum of the light beam. The findings suggest that the optical needle exhibits a long depth of focus and well uniformity, and the full width at half maximum of the transverse field distribution is approximately 0.38 λ beyond the diffraction limit. The uniformity of the optical needle can be tailored by adjusting the width of the primary ring, the decay parameter, and the conical angle. Additionally, the depth of focus of the optical needle significantly improves as the radius of the primary ring increases while still maintaining well uniformity. It may find applications in high-resolution optical imaging and optical manipulation.

Realization of a circularly transformed Airyprime beam with powerful autofocusing ability

The reported autofocusing ability of a ring Airyprime beam array reaches up to 8632.40, while the strongest autofocusing ability of a circular Airyprime beam (CAPB) is only 1822.49. How can the autofocusing ability of a single beam reach the autofocusing ability of a beam array? To achieve this goal, a circularly transformed Airyprime beam (CTAPB) is introduced by following two steps. First, a circular equation transformation on the two transverse coordinates in the electric field expression of a propagating Airyprime beam is performed. Then, the electric field expression of a propagating Airyprime beam is integrated over the angle. The intensity profile of a CTAPB on the initial plane changes significantly with varying the primary ring radius r0. With increasing r0, therefore, the autofocusing ability of a CTAPB undergoes a process of first increasing and then decreasing, while the focal length always increases. A CTAPB exhibits more powerful autofocusing ability than a CAPB. The maximum autofocusing ability of a CTAPB can reach up to 8634.76, which is 4.74 times that of a CAPB, while the corresponding focal length is 95.11% of a CAPB. A CTAPB on the initial plane can be approximately characterized by a ring Airyprime beam array with sufficient number of Airyprime beams. Due to the better symmetry, a CTAPB has a slightly stronger autofocusing ability than a ring Airyprime beam array and almost the same focal length as a ring Airyprime beam array. The CTAPB is also experimentally generated, and the experimental results indicate that the CTAPB has powerful autofocusing ability. As a replacement of a CAPB and a ring Airyprime beam array, this introduced CTAPB can be applied to the scenes which involve abruptly autofocusing effect.

Spin-orbit coupling induced polarization transform in the autofocusing of ring Airy beams with hybrid polarizations

Manipulating polarization is of significance for the application of light. Spin-orbit coupling provides a prominent pathway for manipulating the polarization of light field but generally requires tight focusing conditions or anisotropic media. In this paper, we construct ring Airy beams with hybrid polarizations and reveal the controllable polarization transforms in their autofocusing dynamics by manipulating concomitant spin-orbit coupling in free space. The numerical and experimental results show that the polarization transform is dependent on the azimuthal orders of amplitude and vortex phases of two spin constituents of ring Airy beams, that the focal spots present pure linear polarization whose orientation is determined by the initial phase when the vortex phase topological charge is equal to the amplitude angular factor, otherwise, the focal fields present cylindrical vector polarizations whose orders depend on the difference of amplitude angular orders and topological charges. Our work provides new insights for studying spin-orbit interactions and the depolarization of complex polarization.

Propagation dynamics of the controllable circular Airyprime beam in the Kerr medium

In this paper, we study the propagation dynamics of the circular Airyprime beam (CAPB) in the Kerr medium for the first time. We investigate the effects of the astigmatism factor, the chirp factor, and vortices on the CAPB propagating in the Kerr medium. At the same time, we are also introducing a special-shaped Airyprime beam (SAPB) during its propagation. The transmission characteristics of the CAPB and the SAPB in the Kerr medium are compared under identical conditions. Our theoretical results provide additional possibilities for CAPB modulation in the Kerr medium, thereby promising wider applicability of CAPB in various research areas.

Image transmission with a circular Airy array beam

A circular Airy array beam (CAAB) comprising four symmetric circular Airy beams is proposed and demonstrated for image transmission. It is generated by the Fourier transform of the combined phase, which contains the radial cubic phase, the diffractive axicon phase, and the shift function phase. Two adjustable parameters of the combined phase can control the radius and the initial position of each circular Airy beam at the spatial plane. The image can be modulated into the CAAB through overlapping it at the Fourier plane of this beam and recovered by Fourier transform after diffracting a certain distance. It can be observed clearly that the CAAB after being partly blocked by a movable obstacle guarantees the recovery of the image. In comparison with the existing right-angle Airy array beam, the image transmission by the proposed CAAB is less sensitive to the position of the obstacles on the beam path.

Volume holography-based abrupt autofocusing beam

Volume holographic elements are excellent at shaping high-quality spatial and spectral modes. Many microscopy and laser-tissue interaction applications require precise delivery of optical energy at specific sites without affecting the peripheral regions. Owing to the property of very high energy contrast between the input and the focal plane, abrupt autofocusing (AAF) beams can be the right candidate for laser-tissue interaction. In this work, we demonstrate the recording and reconstruction of a PQ:PMMA photopolymer-based volume holographic optical beam shaper for an AAF beam. We experimentally characterize the generated AAF beams and show the broadband operation property. The fabricated volume holographic beam shaper shows long-term optical quality and stability. Our method offers multiple advantages including high angular selectivity, broadband operation, and intrinsically compact size. The present method may find important applications in designing compact optical beam shapers for biomedical lasers, illumination for microscopy, optical tweezers, and laser-tissue interaction experiments.

Simultaneous trapping of high and low refractive index particles using a single-fiber optical trap with coexisting LP01 and LP11 modes

We propose and demonstrate a fiber optical trap based on the coexistence of LP₀₁ and LP₁₁ modes for the simultaneous trapping of both high refractive index particles and low refractive index particles. Since different mode beams have different propagation constants, they exhibit different focused light fields. We fabricated a tapered fiber probe using thermal fusion to converge the beam, which generates a strong gradient force field near the fiber tip, as well as a dark trap along the axial direction. High refractive index particles are attracted near the fiber tip by a strong gradient force, and low refractive index particles are trapped in the dark cage along the axial direction. The proposed optical trap, which can simultaneously trap particles with different refractive indices, makes it easier to manipulate cells or molecules with different properties and explore multi-molecule interactions, which can facilitate research related to biology and chemistry.

Effect of chirped factors on the abrupt autofocusing ability of a chirped circular Airyprime beam

Recently, a new type of abruptly autofocusing beam called circular Airyprime beam (CAPB) has been reported. Its abrupt autofocusing ability has been proven to be approximately seven times that of a circular Airy beam under the same conditions. Further improving the abrupt autofocusing ability of the CAPB without changing the beam parameters is a concern in optical research. In this study, we investigated the effect of introducing first- and second-order chirped factors on the abrupt autofocusing ability of the CAPB. When the positive first-order chirped factor was below the saturated chirped value, the abrupt autofocusing ability of the chirped CAPB was stronger and the focus position was smaller compared with those of the conventional CAPB. Regarding the abrupt autofocusing ability, there was an optimal value for the first-order chirped factor. At the optimal value, the abrupt autofocusing ability of the chirped CAPB was the strongest. On the other hand, a positive second-order chirped factor promoted the abrupt autofocusing ability of the CAPB and shortened the focus position. The introduction of such value was more effective than the introduction of a positive first-order chirped factor in promoting abrupt autofocusing of the CAPB. The abrupt autofocusing ability of the CAPB was further improved by combining the optimal first-order chirped factor and a positive second-order chirped factor. Finally, the chirped CAPB was experimentally generated, and the corresponding abrupt autofocusing behaviors were measured, validating the theoretical results. Overall, we provide an approach for improving abruptly autofocusing CAPBs.

Optical trapping of multiple particles based on a rotationally-symmetric power-exponent-phase vortex beam

In this paper, the optical trapping of multiple particles based on a rotationally-symmetric power-exponent-phase vortex beam (RSPEPVB) was introduced and demonstrated. Based on the theories of tight focusing and optical force, the optical force model of RSPEPVB was established to analyze the optical trapping force of tightly focused RSPEPVB. Then, an experimental setup of optical tweezer, by utilizing the RSPEPVB, was built to demonstrate that the optical tweezer of RSPEPVBs can achieve the optical trapping of multiple particles, and the number of captured particles is equal to the topological charge l of RSPEPVB, which shows that the RSPEPVBs can achieve multi-particles trapping with controllable number. Moreover, compared to vortex beam, the captured particles by RSPEPVB will not rotate around the circular light intensity distribution. The results will provide a new option for optical trapping of multiple particles in biomedicine, laser cooling and so on.

Autofocusing field constructed by ring-arrayed Pearcey Gaussian chirp beams

In this work, we propose and demonstrate the ring-arrayed Pearcey Gaussian chirp beams (RAPGCBs) synthesized by multiple two-dimensional Pearcey beams. The general analytical formula for the propagation of RAPGCBs is presented. We find that, depending on synthesized number n, the profiles of the beams present different polygonal shapes, and the autofocusing properties can be controlled by chirp factor β. Furthermore, we study the properties of the RAPGCBs carrying optical vortices (OVs). It shows that a single OV or two positive OVs form an autofocusing hollow field, and opposite OVs will annihilate, which results in greatly increased autofocusing ability. Our experimental results agree with the simulations. Such beams have potential applications in particle trapping and biology medical fields.

Theoretical Analysis of Airy–Gauss Bullets Obtained by Means of High Aperture Binary Micro Zonal Plate

We theoretically analyze the methodology for obtaining vectorial three-dimensional bullets, concretely Airy–Gauss bullets. To do this, binary micro zonal plates (BZP) were designed in order to obtain different Airy–Gauss bullets with sub-diffraction main lobe width. Following the vectorial diffraction theory, among the electrical field, we extend the theory to the magnetic field, and thus we analyze several properties such as the Poynting vector and the energy of Airy–Gauss vectorial bullets generated by illuminating the designed BZP with a temporal Gaussian circular polarized pulses.

Abruptly autofocusing of generalized circular Airy derivative beams

In this paper, we introduce a novel kind of abrupt autofocusing beams namely the generalized circular Airy derivative beams (CADBs) as an extension of circular Airy beam (CAB). The propagation dynamics of the CADBs is examined theoretically. Our results show that the CADBs exhibit stronger autofocusing ability than the CAB under the same condition. The physical mechanism of the abruptly autofocusing of the CADBs is interpreted by mimicking the Fresnel zone plate lens. Here, the abruptly autofocusing ability is described by a ratio K = Ifm/I_0m where Ifm and I_0m correspond to the maximum intensities in the focal and the source planes, respectively. As an example, the K-value of the circular Airyprime beam (CAPB, the first-order Airy derivative beam) is about 7 times of that of the CAB. In addition, the CAPB have narrower FWHM (full width at half maxima) in the focus position than the CAB, and the focal spot size of the CAPB is smaller than that of the CAB. Furthermore, we establish an optical system involving a phase-only spatial light modulator to generate the CAPB and measure its autofocusing characteristics experimentally. The measured K-value is about 9.4 percentage error between theory and experiment owing to the imperfection generation of the CAPB. The proposed generalized CADBs will find applications in biomedical treatment, optical manipulation and so on.

Simultaneous Trapping of Two Types of Particles with Focused Elegant Third-Order Hermite-Gaussian Beams

The focusing properties of elegant third-order Hermite-Gaussian beams (TH₃GBs) and the radiation forces exerted on dielectric spherical particles produced by such beams in the Rayleigh scattering regime have been theoretically studied. Numerical results indicate that the elegant TH₃GBs can be used to simultaneously trap and manipulate nanosized dielectric spheres with refractive indexes lower than the surrounding medium at the focus and those with refractive indexes larger than the surrounding medium in the focal vicinity. Furthermore, by changing the radius of the beam waist, the transverse trapping range and stiffness at the focal plane can be changed.

Caustic Interpretation of the Abruptly Autofocusing Vortex beams

We propose an effective scheme to interpret the abruptly autofocusing vortex beam. In our scheme, a set of analytical formulae are deduced to well predict not only the global caustic, before and after the focal plane, but also the focusing properties of the abruptly autofocusing vortex beam, including the axial position as well as the diameter of focal ring. Our analytical results are in excellent agreement with both numerical simulation and experimental results. Besides, we apply our analytical technique to the fine manipulation of the focusing properties with a scaling factor. This set of methods would be beneficial to a broad range of applications such as particle trapping and micromachinings.

Laser manipulation of airborne microparticles behind non-transparent obstacles with the help of circular Airy beams

An approach for the realization of three-dimensional laser manipulation of agglomerations of carbon nanoparticles behind non-transparent obstacles in the air is proposed and investigated. The approach is based on the use of circular Airy beams (CABs), which are structured laser beams with self-healing and autofocusing properties. The possibility to trap and guide both single and multiple microparticles in the case of a non-distorted CAB and a CAB distorted by an on-axis metal rod is demonstrated. We believe that these results open new possibilities for the control of trapped particles that are out of sight and hidden by different obstacles.

Characteristics of an elliptical Airy beam with a circular concentric vortex and its realization

We theoretically and experimentally study the propagation characteristics of elliptical Airy vortex beams (EAVBs) with a circular concentric vortex. It is found that EAVBs inherit the abruptly autofocusing properties of the circular Airy beams (CABs), but EAVBs will have a better autofocusing performance than circular Airy vortex beams (CAVBs) under certain conditions. It is also found that the initial m-order concentric vortex of EAVBs splits into |m| first-order vortices at the autofocusing plane, and the focusing pattern splits into |m|+1 bright spots with the pattern's tilting direction related to the sign of m [m is the topological charge (TC) of the vortex]. These characteristics of EAVBs may have potential applications in TC detection, optical micromanipulation, communications, and other fields.

Autofocusing of ring Airy beams embedded with off-axial vortex singularities

We report the autofocusing behaviors of ring Airy beams (RABs) embedded with two kinds of off-axial vortex singularities. The influences of embedded positions and topological charges of point and r vortices on the autofocusing dynamic are numerically and experimentally investigated. The results show that, for the first-order vortex, the embedded position significantly affects the focal field, and once the singularity is located on the main ring of RAB, the symmetric Bessel profile of the focal field will be broken, otherwise the Bessel-like focus can self-heal at the focal plane. However, for the higher-order vortex embedded near the main ring, it will split into several fundamental vortices and then separate with each other along the radial direction under the interaction with the RAB background. Our results hold potential for the practical application of RABs in the atmosphere and other propagation systems with perturbation and even singularities.

Enhancement of trapping efficiency by utilizing a hollow sinh-Gaussian beam

Propagation properties and optical forces upon a Rayleigh dielectric sphere for a newly proposed hollow sinh-Gaussian beam (HsGB) are intensively investigated. In view of the targeted laser beam’s unique tight focusing properties that a significantly sharp, peak-centered, and adjustable intensity distribution would be produced in the focal vicinity, the tightly focused HsGB could be exploited to trap and manipulate nano-sized dielectric spheres with high-refractive index in the focal region. The interesting and meaningful features for the novel HsGB mainly include that, compared with the conventional fundamental Gaussian beams under the same optical power, the tightly focused HsGB has much higher intensity gradient and deeper potential well through optimizing targeted laser beam’s parameters. Theretofore, the novel HsGB optical tweezers could drastically enhance its trapping efficiency. Finally, the trapping stability conditions are discussed in detail. The analytical and numerical results obtained here could provide a directive suggestion for researchers in optimizing experimental parameters in constructing a novel HsGB tweezers and making use of a HsGB.

Besinc Pseudo-Schell Model Sources with Circular Coherence

Partially coherent sources with non-conventional coherence properties present unusual behaviors during propagation, which have potential application in fields like optical trapping and microscopy. Recently, partially coherent sources exhibiting circular coherence have been introduced and experimentally realized. Among them, the so-called pseudo Schell-model sources present coherence properties that depend only on the difference between the radial coordinates of two points. Here, the intensity and coherence properties of the fields radiated from pseudo Schell-model sources with a degree of coherence of the besinc type are analyzed in detail. A sharpening of the intensity profile is found for the propagated beam by appropriately selecting the coherence parameters. As a possible application, the trapping of different types of dielectric nanoparticles with this kind of beam is described.

Abruptly autofocusing property of circular Airy vortex beams with different initial launch angles

Controlling the trajectory of circular Airy beams (CABs) by negative launch angles would greatly reduce their abruptly autofocusing property. By numerically simulating the propagation of a circular Airy vortex beam with different initial launch angles, we demonstrate in this paper that a larger topological charge of optical vortex (OV) is quite helpful to enhance the abruptly autofocusing property under different launch angles (especially for negative launch angles), without affecting the focal position and trajectory. Two opposite OVs would attract each other and partially overlap in the focal plane of CAB under different launch angles, causing even stronger autofocusing. As the distance between two OVs increases, the focal intensity contrast would decrease, especially for a beam with positive launch angles, whose autofocusing property decreases much more quickly with the distance.

Controlling abruptly autofocusing vortex beams to mitigate crosstalk and vortex splitting in free-space optical communication

Orbital angular momentum (OAM) mode crosstalk induced by atmospheric turbulence is a challenging phenomenon commonly occurring in OAM-based free-space optical (FSO) communication. Recent advances have facilitated new practicable methods using abruptly autofocusing light beams for weakening the turbulence effect on the FSO link. In this work, we show that a circular phase-locked Airy vortex beam array (AVBA) with sufficient elements has the inherent ability to form an abruptly autofocusing light beam carrying OAM, and its focusing properties can be controlled on demand by adjusting the topological charge values and locations of these vortices embedded in the array elements. The performance of a tailored Airy vortex beam array (TAVBA) through atmospheric turbulence is numerically studied. In a comparison with the ring Airy vortex beam (RAVB), the results indicate that TAVBA can be a superior light source for effectively reducing the intermodal crosstalk and vortex splitting, thus leading to improvement in the FSO system performance.

Effects of a modulated vortex structure on the diffraction dynamics of ring Airy Gaussian beams

The evolution of the ring Airy Gaussian beams with a modulated vortex in free space is numerically investigated. Compared with the unmodulated vortex, the unique property is that the beam spots first break up, and then gather. The evolution of the beams is influenced by the parameters of the vortex modulation, and the splitting phenomenon gets enhanced with multiple rings becoming light spots if the modulation depth increases. The symmetric branch pattern of the beam spots gets changed when the number of phase folds increases, and the initial modulation phase only impacts the angle of the beam spots. Moreover, a large distribution factor correlates to a hollow Gaussian vortex shape and weakens the splitting and gathering trend. By changing the initial parameters of the vortex modulation and the distribution factor, the peak intensity is greatly affected. In addition, the energy flow and the angular momentum are elucidated with the beam evolution features being confirmed.