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Programmable metasurfaces show enormous potential in real-time electromagnetic (EM) manipulation and their stable responses to variable EM waves including incident angle and polarization changes are crucial for related applications. However, the demonstrated programmable metasurfaces are commonly considered in normal-incident waves with fixed polarization; how to achieve stable performance in more realistic scenarios of wide-angle and full-polarized wave incidences is still a challenge. Here, we propose and realize a wide-angle and full-polarization programmable metasurface, which can generate stabilized amplitude and phase responses at both transverse electric (TE) and transverse magnetic (TM) oblique incidences. These are achieved by introducing metallic walls around the metasurface element to reduce element coupling, which greatly improves the angular stability of its reflection responses. The mechanisms of angular insensitivity are analyzed comprehensively, and as a proof of concept, obliquely-incident beam steering, large-angle beam scanning and oblique vortex beam emitting are demonstrated on this programmable metasurface. Both the simulation and experimental results demonstrate that the programmable metasurface can operate well at both TE and TM wide-angle oblique incidences in the upper half space. Our work offers an actual route for improving the angular stability and polarization insensitivity of metasurfaces, which could push them one step closer towards more complicated applications. [ABSTRACT FROM AUTHOR]

We propose a novel technique for multi-image encryption and hiding schemes under an optical asymmetric framework using structured fingerprint phase masks (SFPMs) in the gyrator transform (GT) domain and three-step phase-shifting digital holography (PSDH). A SFPM contains unique features of fingerprint and structured phases of the optical vortex beam, which provides enhanced security in the cryptosystem. To encrypt multiple images, GT-based phase truncation and phase reservation techniques have been used in the first level of security, whereas three-step PSDH has been used to obtain the final cipher text. The cipher text is embedded in the host image to perform the watermarking process. In this process, the host is further decomposed into three parts in which anyone from the last two parts can be used for watermark embedding, and the first part is stored as the key. The use of polar decomposition in the watermarking process provides an additional layer of security. Numerical simulations and experimental results are presented to support the proposed scheme. [ABSTRACT FROM AUTHOR]

Polarization detection has been widely used in various fields, especially in free-space optical communication associating with orbital angular momentum (OAM). However, the bulky optical devices and the complexity of the detection process have hindered the integration and miniaturization of communication systems. Herein, a novel polarization detection method is proposed to directly identify the polarization state of incident light based on the normalized spectra of the sorted OAM modes which are converted from a composite vortex beam (CVB) to a set of spatial distinct strip type beams (STBs). The polarization states of light beam can be apparently distinguished via the combination of different STBs without redundant detection elements and the system demonstrates great robustness under specific atmospheric turbulence as well. The introduction of such a polarization detection method in future communication links will obtain lower complexity and consumption, which is very favorable regarding OAM communications. [ABSTRACT FROM AUTHOR]

A new method is proposed for the characterization of the atmospheric turbulence strength parameter ( C n 2 ) based on the principal component analysis (PCA) of the texture of the speckle intensity pattern obtained on long-range propagation of a focused charge +1 vortex beam. Employing the split-step propagation method, datasets containing instantaneous intensity images of the focused vortex beam are generated for three distinct C n 2 values, specifically 1 × 10 − 14 m − 2 / 3 , 5 × 10 − 14 m − 2 / 3 , and 1 × 10 − 13 m − 2 / 3 , representing medium to high turbulence levels for a 2 km propagation distance. The gray level co-occurrence matrix (GLCM) methodology is employed to extract key texture attributes, like contrast, correlation, homogeneity, and energy from the intensity images. These extracted texture parameters serve as inputs for training a PCA model, enabling the identification of associated C n 2 values. The PCA analysis exhibits distinct clustering of the first three principal components for each of the three C n 2 values, forming individual clusters on the PCA plot. Standard deviational ellipses are drawn to clearly demarcate these clusters on the PCA plot. The texture-based PCA classification of atmospheric turbulence was also performed for a focused Gaussian beam. The comparison of PCA plots between vortex and Gaussian beams showed that a pronounced clear separation of C n 2 values is obtained for the vortex beam. This indicates that the non-zero orbital angular momentum of the vortex beam also plays an important role in achieving the distinct separation of C n 2 values on the PCA plot. The proposed method can provide efficient real-time turbulence estimation solely on the basis of texture of the instantaneous intensity speckle with prior training and therefore may simplify the estimation of turbulence strength parameter. [ABSTRACT FROM AUTHOR]

Vector beams display varying polarisation over planes transversal to their direction of propagation. The variation of polarisation implies that the electric field cannot be expressed as a product of a spatial mode and its polarisation. This non-separability has been analysed for particular vector beams in terms of non–quantum entanglement between the spatial and the polarisation-degrees of freedom, and equivalently, with respect to the degree of polarisation of light. Here we demonstrate theoretically and experimentally that Mathieu–Gauss vector modes violate a Bell-like inequality known as the Clauser–Horn–Shimony–Holt–Bell inequality. This demonstration provides new insights on the violation of Bell inequalities by a more general class of vector modes with elliptical symmetry. [ABSTRACT FROM AUTHOR]

The precondition for the application of light beams is the ability to devise light distribution with high precision. Controlling more dimensions for structured light fields is an effective method to improve the ability to devise light distribution. The Swallowtail beam, due to its rich regulatory parameters, provides the possibility to design a light field with a specific intensity distribution. Utilizing the Swallowtail beam as a foundation, we design its initial phase, polarization, and coherent structure, and propose a partially coherent azimuthally polarized circular vortex Swallowtail Gaussian beam (PCAPCVSGB) in our paper. This beam exhibits an abnormal self-focusing ability and forms an easily adjustable optical potential well at the focal plane, providing another effective tool for achieving optical manipulation. In addition, the PCAPCVSGB also shows an interesting vector property. It possesses a stable polarization singularity even with changes in coherence and topological charges, which exhibits a potential application value in optical communication. [ABSTRACT FROM AUTHOR]

The bound state in the continuum (BIC) is a singular point of polarization in the momentum space of a periodic structure. It has been demonstrated that vortex beams can be generated by utilizing the polarization vortex around BIC based on the geometric phase in momentum space. In this letter, we propose a reflective photonic crystal (PhC) to generate a vortex beam and demonstrate the superimposition of topological charges in the momentum space between PhC and the vortex beams. In addition to BICs, we demonstrate that other singularities like degenerate points can also be used to generate vortex beams. [ABSTRACT FROM AUTHOR]

The orbital angular momentum (OAM) has been widely studied and applied to many scientific fields, especially in optical communication and quantum information. In order to give full play to the high-dimensional characteristics of OAM, separating different OAM states is a fundamental requirement. Here we find a way to introduce the mode dependent phase shift by using Porro prism, design and manufacture a new kind of two-output OAM sorter. Our OAM sorter can separate two OAM states with different topological charges without destroying them. Because it is composed of several linear commonly optical elements, which can be closely pasted together, our OAM sorter is very compact and sturdy. Furthermore, by means of cascading, our design can be used for constructing an OAM sorter with multiple output ports. Therefore, our research should have great potential application prospects, especially in the communication protocol based on OAM. [ABSTRACT FROM AUTHOR]

We study the propagation of non-isotropically correlated vector vortex beams (NCVVBs) through an ABCD optical system. The statistical properties, namely, intensity, state of polarization, degree of polarization (DoP), and degree of coherence (DoC) of these beams are investigated. The terminology non-isotropically correlated is used for electromagnetic Gaussian Schell-model beams, that exhibit the distinguishability of spatial correlations between parallel and orthogonal electric field components. The non-isotropic feature of the correlation widths introduces an azimuthal asymmetry in the intensity, DoP, and DoC distributions. The azimuthal asymmetry in the intensity and DoC distributions become prominent around the focal plane. However, this asymmetry can be clearly observed in DoP distributions even at a very short propagation distance. It is found that the statistical properties of NCVVBs are dependent on both Poincaré–Hopf index (PHI) and the source correlation parameters. The number of beamlets in the intensity distribution is twice the magnitude of the PHI of the input beam. Unlike isotropically correlated vector vortex beams, correlation-induced polarization around the central core of the NCVVB is observed. The DoC distribution exhibits the evolution of correlation singularities in the form of dislocations at the far field plane. These dislocations in the DoC profile under lower correlations depend on the PHI, which provides a feasible approach to measure the index of NCVVBs. This study provides a technique to synthesize beams with structured correlation and polarization features. [ABSTRACT FROM AUTHOR]

We propose an atomic grating based on an electromagnetically induced transparency phenomenon that switches between zeroth-order diffraction to a distinct higher-order diffraction pattern by driving a planar gaseous medium of a four-level tripod ( ⋔) atoms with three laser beams: modulation of standing wave control beam propagating nearly perpendicular to the planar medium, while vortex and weak plane probe beams directed perpendicular to the medium. We numerically investigate the behavior of the amplitude, phase modulations, and probe field diffraction intensities of different orders by the variation of the field detunings and orbital angular momentum number of the composite vortex light beam. Specifically, in the off-resonant case, the interplay between a square lattice of the control and an additional spatial variation of the vortex beam allows the emergence of higher diffraction orders and variable gain due to double transparency windows in this complex optical system. We believe that our proposed scheme might be useful in optical memory devices via the storage of information to diffraction orders of the atomic grating. [ABSTRACT FROM AUTHOR]

Vector beams with spiral phase and spatially varying polarization profiles have many applications from optical micromanipulation to materials processing. Here, we propose and demonstrate an atomic spatial mode extracting scheme for the vector beam based on polarization-dependent absorption in the atom vapor. By employing the linear polarization pump beam which induces polarization sensitive absorption in the atomic ensemble, a counter-propagated weak probe vector beam is extracted by spatial absorption, and extracted part still maintains the original polarization and the vortex phase. The topological charges of the extracted mode are verified by interfering with the Gaussian beam, and it can be found that the orbital angular momentum is conserved in the extracting process. Our work will have potential applications in non-destructive spatial mode identification, and is also useful for studying higher-dimensional quantum information based on atomic ensembles. [ABSTRACT FROM AUTHOR]

In this manuscript, we put forward two new types of structured light beams, the vortex Pearcey–Gauss (VPeG) beam, with a homogeneous polarisation distribution, and the vector VPeG (VVPeG) beam, with a non-homogeneous polarisation distribution. The latter is generated as a non-separable superposition of the spatial and polarisation degrees of freedom of light. We achieve their experimental realization through the combination of a spatial light modulator, which creates a scalar Pearcey–Gauss beam, and a q -plate which transforms it into a vortex or a vortex vector beam, depending on its input polarisation state. Their intensity and polarisation distributions along the propagation direction were determined through Stokes polarimetry, which was compared with numerical simulations. As demonstrated, the VVPeG beam evolves from an all-linear polarisation distribution to an approximately full Poincaré beam. The proposed vector beams add to the extensive family of non-separable states of light. We anticipate that both types of beams will find applications in fields as diverse as optical metrology and tweezers, amongst others.

Spin-selective multi-functional integrated metasurfaces have attracted much research attention due to its promising application prospects. However, the goal of independent and arbitrary control of both amplitude and phase for orthogonal circularly polarized (CP) waves still has not been achieved fully. This is because it requires mirror asymmetric structure to achieve such a goal but there is no apparent physical relation between the unit cell structure and the spin-selective properties. A simple method with clear physical pictures is proposed in this paper to achieve the goal of arbitrary spin-selective manipulations. The idea is to convert the incident orthogonal CP waves to orthogonal linearly polarized (LP) waves first, then manipulate the LP waves with matured techniques, and finally convert the LP waves back to the corresponding CP waves. Simulations and experiments have been carried out to validate the method. Using this idea, spin-selective focusing, spin-selective deflection and spin-selective orbital angular momentum vortex beam have been demonstrated. [ABSTRACT FROM AUTHOR]

Vortex beam carrying orbital angular momentum (OAM) reveals essential application potential in regimes ranging from communication to high-resolution imaging due to the capability to expand channel capacity. However, many current methods for generating vortex beams suffer from narrow bandwidth, low efficiency, and high profile, which undoubtedly will limit their practical application. In this paper, a microwave ultra-wideband single-layer Pancharatnamâ€"Berry metasurface is proposed to convert incident plane waves into vortex waves. The proposed novel stacked-arc-shaped meta-atoms of the metasurface can realize high-performance spin angular momentum-OAM conversion with the efficiency of more than 83% within a considerable bandwidth from 5.85 to 19.56 GHz (fractal bandwidth of 108%), which achieves high-efficiency operation within a wider bandwidth compared to some other wideband metasurface-based vortex beam generator. Three metasurface prototypes for generating vortex beams with the topological charges of l = ±2, âˆ'1, âˆ'3 respectively are designed. In addition, a metasurface for generating a vortex beam with the topological charge of l = ±2 is fabricated as an example to demonstrate the feasibility and high performance of our vortex beam generator. The generated vortex beams with the mode order of ±2, âˆ'1, âˆ'3 both in the near-field and the far-field zone are simulated theoretically and the generated vortex beam with the mode order of l = âˆ'2 is measured experimentally. The results of the simulation and experiment coincide with each other, which verified the proposed vortex beam generation method successfully. The proposed vortex beam generator is valuable and user-friendly in practical application because of the advantages of low profile, ultra-wide bandwidth, high efficiency, and easy fabrication. [ABSTRACT FROM AUTHOR]

Manifestations of orbital angular momentum induced effects in the diffraction of a radially polarized vector beam by an off-axis tilted aperture are studied both experimentally and theoretically. Experiments were carried out to extract the degree of circular polarization, which was shown to be proportional to the on-axis component of the spin angular momentum density. We report a clear separation of the regions of dominance of the right and left circular polarizations associated with positive and negative topological charges respectively, which is reminiscent of the standard vortex-induced transverse shift, albeit in the diffraction scenario. The experimental results are supported by model simulations and the agreement is quite satisfactory. The results are useful to appreciate the orbit-orbit related effects due to unavoidable misalignment problems (especially for vortex beams). [ABSTRACT FROM AUTHOR]

Self-healing of light refers to the ability of a light field to recover its structure after being damaged by a partial obstruction placed in its propagation path. Here, we will give a comprehensive review of the history and development of self-healing effects, especially highlighting its importance in vector vortex beams carrying spin and orbital angular momenta. Moreover, an unified zoology of self-healing, structured light is proposed to unveil a deeper understanding of its physical mechanism and provide a bird’s eye view on diverse forms of self-healing effects of different kinds of complex structured light. Finally, we outline the open challenges we are facing, potential opportunities and future trends for both fundamental physics and applications. [ABSTRACT FROM AUTHOR]

Metamaterial (MM) based on double-split resonator and vanadium dioxide (VO2) in terahertz (THz) region is proposed in this paper, which integrates broadband absorption (ABS) and generation of vector beams. Simulation results show that by tuning the VO2 into metallic phase, the ABS of proposed MMs achieves over 90% in 1.35â€"2.18 THz. The physical mechanism of broadband ABS is clarified by introducing the impedance matching theory and distributions of electric field. Moreover, ABS characteristics of the designed MMs at different polarization angles and incident angles are also studied, respectively. While VO2 is in insulated state, simulation results indicate that the radial polarized beam and the angular polarized beam can be generated when the incident wave is x -polarization and y -polarization, respectively. The polarization conversion rate over 90% is realized between 1.37 THz and 2.20 THz within the incident angle of 10°. The bi-functional MMs proposed in this paper has promising applications in modulators, imaging and sensors. [ABSTRACT FROM AUTHOR]

Complex vector modes of light, non-separable in their spatial and polarisation degrees of freedom, are revolutionising a wide variety of research fields. It is therefore not surprising that the generation techniques have evolved quite dramatically since their inception. At present it is common to use computer-controlled devices, among which digital micromirror devices have become popular. Some of the reason for this are their low-cost, their polarisation-insensitive and their high-refresh rates. As such, in this manuscript we put forward a novel technique characterised by its high stability, which is achieved through a common-path interferometer. We demonstrate the capabilities of this technique experimentally, first by generating arbitrary vector modes on a higher-order Poincaré sphere, secondly, by generating vector modes in different coordinates systems and finally, by generating various vector modes simultaneously. Our technique will find applications in fields such as optical manipulations, optical communications, optical metrology, among others. [ABSTRACT FROM AUTHOR]

This paper used femtosecond Gaussian and vortex beams to ablate a Cu target and generate Cu plasmas. A Gaussian beam pulse is shaped into a vortex beam by a vortex wave plate (topological charge m = 1). The spectral intensity of Cu plasmas produced by the two lasers was measured, finding that the spectra with vortex beam were stronger than that with Gaussian beam. The spectral intensity was doubled by simply changing the Gaussian beam into the vortex beam. In addition, the position for maximum Cu atomic line emission along with the laser path was closer to the position of focusing-lens with increasing laser energy. Finally, the Boltzmann plot calculated the plasma temperature, finding that the plasma temperature with the vortex beam was also higher than that with the Gaussian beam. The results indicated that vortex beams could improve the spectral intensity of the femtosecond laser-induced plasmas. [ABSTRACT FROM AUTHOR]

Vector vortex beams play an important role in tailoring tightly focused fields by creating an additional longitudinal component at the focal plane. Until now, mainly focusing properties of fundamental, higher order vector fields and negative indexed ellipse fields have been investigated. In this paper we numerically analyze tight focusing behaviour of ellipse fields embedding C-point singularities of index I C = ± 1 2 , I C = ± 1 , I C = ± 3 2 and I C = ± 2. We show that both the sign and absolute value of C-point index (I C ) of the ellipse fields play an important role in tailoring the focal intensity landscapes. For negative index C-points the intensity distribution of the longitudinal components show symmetries that correspond to the number of separatrices present in the polarization distribution. At the focal plane, both transverse and longitudinal components of the ellipse fields are found to be embedded with phase singularities. These ellipse fields can be useful in advanced microscopy for shaping the focus of light fields for various applications. [ABSTRACT FROM AUTHOR]

In this work, we present an introduction to the field of spatially partial coherent beams, while keeping in mind the transverse structure of an optical field. We look closely at the concept of spatial coherence and show some strategies to deal with it. We work stepâ€"byâ€"step with the reader and construct as an example, a partially coherent vortex beam. Finally, using numerical simulations, the richness in structure of a partially coherent field is revealed through its crossâ€"correlation function. [ABSTRACT FROM AUTHOR]

Rotational manipulation of massive particles and biological samples is essential for the development of miniaturized lab-on-a-chip platforms in the fields of chemical, medical, and biological applications. In this paper, a device concept of a two-dimensional acoustofluidic chamber actuated by multiple nonlinear vibration sources is proposed. The functional chamber enables the generation of acoustic streaming vortices for potential applications that include strong mixing of multi-phase flows and rotational manipulation of micro-/nano-scale objects without any rotating component. Using numerical simulations, we find that diversified acoustofluidic fields can be generated in the chamber under various actuations, and massive polystyrene beads inside can experience different acoustophoretic motions under the combined effect of an acoustic radiation force and acoustic streaming. Moreover, we investigate and clarify the effects of structural design on modulation of the acoustofluidic fields in the chamber. We believe the presented study could not only provide a promising potential tool for rotational acoustofluidic manipulation, but could also bring this community some useful design insights into the achievement of desired acoustofluidic fields for assorted microfluidic applications. [ABSTRACT FROM AUTHOR]

The Pancharatnamâ€"Berry phase induced by the winding topology of polarization around a vortex singularity at bound states in the continuum (BIC) provides a unique approach to optical vortex (OV) generation. The BIC-based OV generators have the potential to outperform their counterparts that rely on spatial variations in terms of design feasibility, fabrication complexity, and robustness. However, given the fact that this class of OV generators originates from the topological property of the photonic bands, their responses are generally fixed and cannot be dynamically altered, which limits their applications to photonic systems. Here, we numerically demonstrate that a silicon photonic crystal slab can be used to realize optically switchable OV generation by simultaneously exploiting the vortex topology in momentum space in conjunction with silicon’s nonlinear dynamics. Picosecond switching of OV beams at near-infrared wavelengths are observed. The demonstrated nontrivial topological nature of the active generators can significantly expand the application of BIC toward ultrafast vortex beam generation, high-capacity optical communication, and mode-division multiplexing. [ABSTRACT FROM AUTHOR]

Vortex beam (VB) possessing spatially helical phaseâ€"front has attracted widespread attention in free-space optical communication, etc. However, the spiral phase of VB is susceptible to atmospheric turbulence, and effective retrieval of the distorted conjugate phase is crucial for its practical applications. Herein, a convolutional neural network (CNN) approach to retrieve the phase distribution of VB is experimentally demonstrated. We adopt a spherical wave to interfere with VB for converting its phase information into intensity changes, and construct a CNN model with excellent image processing capabilities to directly extract phaseâ€"front features from the interferogram. Since the interference intensity is correlated with the phaseâ€"front, the CNN model can effectively reconstruct the wavefront of conjugate VB carrying different initial phases from a single interferogram. The results show that the CNN-based phase retrieval method has a loss of 0.1418 in the simulation and a loss of 0.2344 for the experimental data, and remains robust even in turbulence environments. This approach can improve the information acquisition capability for recovering the distorted wavefront and reducing the reliance on traditional inverse retrieval algorithms, which may provide a promising tool to retrieve the spatial phase distributions of VBs. [ABSTRACT FROM AUTHOR]

Tunable metasurface devices are considered to be an important link for metasurfaces to practical applications due to their functional diversity and high adaptability to application scenarios. Metasurfaces have unique value in the generation of vortex beams because they can realize light wavefronts of any shape. In recent years, several vortex beam generators using metasurfaces have been proposed. However, topological charge generally lacks tunability, which reduces the scope of their applications. Here, we propose an active tunable multi-channeled vortex beam switch based on a moirĂ© structure composed of two cascaded dielectric metasurfaces. The simulation results show that when linearly polarized light with a wavelength of 810 nm is incident, the topological charge from âˆ'6 to +6 can be continuously generated by relatively rotating the two metasurfaces. Meanwhile, different topological charges are deflected to different spatial channels, realizing the function of multi-channeled signal transmission. We also study the efficiency and broadband performance of the structure. The proposed multi-channel separation method involving vortex beams that can actively tune topological charges paves the way for the compactness and functional diversity of devices in the fields of optical communications, biomedicine, and optoelectronics. [ABSTRACT FROM AUTHOR]

Switchable metasurfaces with diversified functionalities have become an emerging research area owing to its potential for realizing integrated and miniature meta-devices. Although great efforts have been devoted in this area, switchable metasurfaces with diversified functionalities still require dealing with formidable challenges. In this paper, a switchable broadband terahertz (THz) metasurface with multiple functionalities is proposed utilizing the phase transition property of vanadium dioxide (VO2), and it can switch functionalities by changing the state of VO2 from metal to insulator thermally. The simulation results demonstrate that when VO2 is in metallic state at the temperature of 400 K, the designed metasurface works as a half wave plane with polarization conversion ratio more than 90% at THz frequency band ranging from 0.66 to 1.44 THz. When VO2 is in insulating state at the temperature of 300 K, the metasurface can flexibly control the phase of the THz wave. As a proof of concept, several devices with high performance for realizing anomalous reflection, diffuse scattering, vortex beam and beam-focusing are numerically investigated. The proposed metasurface has potential applications in THz imaging, sensing and other intellectual systems for photonics integration. [ABSTRACT FROM AUTHOR]

We suggest a scheme that consists of a cavity with a four-level double Λ atomic medium as an intracavity medium. The reflection of an optical vortex light beam field that is incident on a cavity has been investigated by consideration within the coherence theory framework. We study the influence of the orbital angular momentum (OAM) of the vortex light beam on the lateral or Goosâ€"Hänchen shift (GHS) for the reflected beam. It has been investigated that different values of OAM from the incident vortex beam enhanced positive and negative GHS. Also, we consider two fields (including incident) that carry an optical vortex interacting with the cavity. We obtain giant positive and negative GHS via manipulation of the OAM corresponding to the two optical vortex beams. To the best of our knowledge, no one has ever studied such a large GHS in a reflected beam. [ABSTRACT FROM AUTHOR]

Electromagnetic energy backflow is a phenomenon that occurs in regions where the direction of the Poynting vector is opposite to that of the propagation of the wave field. It is particularly remarkable in the nonparaxial regime and has been exhibited in the focal region of sharply-focused beams, for vector Bessel beams, and vector-valued spatiotemporally localized waves. A detailed study is undertaken of this phenomenon and the conditions for its appearance are examined in detail in the case of a superposition of four plane waves in free space, the simplest electromagnetic arrangement for the observation of negative energy flow, as well as its comprehensive and transparent physical interpretation. It is shown that the state of polarization of the constituent components of the electromagnetic plane wave quartet determines whether or not energy backflow takes place and what values the energy flow velocity assumes. Depending on the polarization angles, the latter can assume any value from c (the speed of light in vacuum) to −c in certain spatiotemporal regions of the field. [ABSTRACT FROM AUTHOR]

A general Matlab program is designed to simulate the Fraunhofer diffraction patterns of a vortex beam through any apertures, which are usually used to compare with the experimental results in detecting the topological charge of a vortex beam. Two significant matrices are suggested in the above program: one related to the aperture, the other concerned with the field of vortex beam. Using the fast Fourier transform function provided within the Matlab software itself to process the dot product of the above two matrices, one obtains the field on the observation screen. The program is applied to a rectangular aperture and an annular triangle aperture. The results agree well with the computational analysis of previous references. This paper is to describe how Matlab can be used to perform complex mathematical calculations without bogging down the student with the details of the numerical methods and it may be particularly useful for both upper-level undergraduates and graduate students who engage in the study of topological charge detection and identification. [ABSTRACT FROM AUTHOR]

We experimentally study the femtosecond supercontinuum (SC) generation using an optical vortex (OV) beam in water. It is demonstrated that the topological charge of the OV beam has little influence on spectral broadening induced by filament, while it has strong influence on spectral intensity. Despite the SC induced by filamentation of optical vortices in air possesses orbital angular momentums (OAMs), the SC generated in water and sapphire loses OAM. However, the light at central wavelength possesses OAMs after filamentation in transparent Kerr media. This study is helpful to the understanding of the physical mechanism of femtosecond SC generation by optical vortices in water. [ABSTRACT FROM AUTHOR]

Due to the large exciton binding energy, two-dimensional (2D) transition metal dichalcogenides (TMDCs) provide an ideal platform for studying excitonic states and related photonics and optoelectronics. Polarization states lead to distinct light-matter interactions which are of great importance for device applications. In this work, we study polarized photoluminescence spectra from intralayer exciton and indirect exciton in WS2 and WSe2 atomic layers, and interlayer exciton in WS2/WSe2 heterostructures by radially and azimuthally polarized cylindrical vector laser beams. We demonstrated the same in-plane and out-of-plane polarization behavior from the intralayer and indirect exciton. Moreover, with these two laser modes, we obtained interlayer exciton in WS2/WSe2 heterostructures with stronger out-of-plane polarization, due to the formation of vertical electric dipole moment. [ABSTRACT FROM AUTHOR]

Vortex beams carrying orbital angular momentum (OAM) have aroused great interest of both scientific and engineering communities. Encouragingly, generating OAM with different topological charges in a shared aperture is regarded as a potential route to expanding the communication capacity, which yet is an academic challenging task. In this work, a paradigm of designing metasurface-based shared aperture antenna for generating polarization-dependent vortex beams with distinct topological charges is proposed. Anisotropic unit cells that can tailor different resonance phase profiles in two orthogonal orientations are used to assemble a metasurface reflector. As a proof-of-concept, a planar reflector antenna is designed with two Vivaldi sources, which can generate x- and y-polarized vortex beams with topological charges of l = –1 and l = –2, respectively. Both the simulation results and the measurement results are in good agreement, which demonstrates the feasibility of our design. Significantly, this work provides a new route to achieving vortex beams carrying different topological charges in the same frequency band, which may have potential applications in communication systems. [ABSTRACT FROM AUTHOR]

We investigate the effect of density down-ramps on the acceleration of ions via magnetic vortex acceleration in a near-critical density gas target by means of particle-in-cell simulations. The spin-polarization of the accelerated protons is robust for a variety of ramp lengths at around 80%. Significant increase of the ramp length is accompanied by collimation of low-polarization protons into the final beam and large transverse spread of the highly polarized protons with respect to the direction of laser propagation. [ABSTRACT FROM AUTHOR]

We propose a controllable exponential-Cosine Gaussian vortex (ECGV) beam, which can evolve into the different beam profiles with three parameters: distance modulation factor (DMF), split modulation factor (SMF) and rotation modulation factor (RMF). When SMF is 0, the ECGV beam appears as a perfect single-ring vortex beam and the ring radius can be adjusted by the DMF. We deduce from mathematics and give the reason for the single-ring characteristics. When SMF is not 0, the beam splits symmetrically. DMF, SMF and RMF control the number, distance and rotation angle of the split, respectively. Our experiments verify the correctness of the theory. [ABSTRACT FROM AUTHOR]

It has been confirmed beams carrying total angular momentums (TAMs) that consist of spin angular momentums (SAMs) and orbital angular momentums (OAMs) are widely used in classical and quantum optics. Here we propose and demonstrate a new kind of representation consisting of four real numbers to describe the TAM states of arbitrary beams. It is shown that any homogeneous polarization, scalar vortices and complex vectorial vortex field, all of which result from the TAMs of photons, can be well represented conveniently using our proposed four-parameter representation. Furthermore, the proposed representation can also reveal the internal change of TAMs as the conversion between SAMs and OAMs. The salient properties of the proposed representation is to give a universal form of TAMs associated with complicated polarizations and more exotic vectorial vortex beams, which offer an important basis for the future applications. [ABSTRACT FROM AUTHOR]

Vortex beams carrying orbital angular momentum (OAM) are expected to efficiently increase channel capacity in communication sectors, so ultra-broadband vortex beam generators with high performance are important in next-generation communication systems. Based on the concept of the Pancharatnam–Berry phase, we propose a metasurface with an H-shaped resonator for realizing vortex beam generation within an ultra-wideband frequency range from 7.3 to 21 GHz (relative bandwidth = 96.8%). The designed meta-atom can acquire high efficiency (efficiency ≥ 92%) conversion from the incident plane wave to the reflected vortex wave across the entire frequency band. To verify the performance of the proposed metasurface, a reflective array consisting of 18 × 18 single-layered elements with different rotated angles is simulated for generating the vortex beam with a topological charge of ±2. Through OAM spectral analysis, the left-handed components of the reflected electric fields and mode purity of the generated vortex beams under different frequencies are achieved and discussed in detail. Then the metasurface is fabricated and measured, and the numerical and experimental results coincide well, proving the effectiveness and high performance of the proposed design. [ABSTRACT FROM AUTHOR]

We consider collinear acousto-optic diffraction of circularly polarized optical waves at circularly polarized acoustic waves in the crystals that reveal both acoustic conical refraction and optical activity. We find that, due to the conical refraction of acoustic waves, these waves produce vector-vortex beam. In this process, the orbital angular momentum (OAM) of the conically refracted acoustic wave is transformed into the OAM of the diffracted optical wave. At the same time, the spin angular momentum of conically refracted phonons is transferred to diffracted photons. The possibility of phonon-photon entanglement is discussed in the work. [ABSTRACT FROM AUTHOR]

THz-based technologies and research applications have seen a rapid increment in recent period together with the development of novel radiation sources based both on relativistic electrons and laser techniques. In this framework, laser-induced plasma filament plays an important role in generating intense and broadband THz radiation. Although many attentions have been paid to THz emission from two-color plasma filaments, one-color plasma emission has been scarcely investigated. In particular, the polarization state of one-color THz emission is still controversial due to the limitations of the existing THz detection techniques, which are incapable of simultaneously detecting elliptically and radially polarized THz radiation. In this manuscript, we develop a novel detection method and unambiguously demonstrate for the first time that one-color laser-induced plasma filament simultaneously emits elliptically and radially polarized THz radiation. These polarization states suggest that the generation mechanism results from electric quadrupole, showing a new route for producing more complex polarization states and THz vortex beams. [ABSTRACT FROM AUTHOR]

Perfect optical vortices (POVs) arevortex beams with infinitely narrow rings and fixed radii independent of their topological charges. Here we propose the concept of generalized POVs (GPOVs) along arbitrary curves beyond the regular shapes of circles and ellipses. GPOVs share similar properties to POVs, such as defined only along infinitely narrow curves and owning topological charges independent of scale. Using a rigorous mathematical derivation in a curvilinear coordinate, we reveal theoretically that the GPOVs have a topological charge proportional to the area of the swept sector in tracing the curve, suggesting a unique mode for optical vortex beams. Experimentally, the complex-amplitude masks to generate the GPOVs are realized by using a pure-amplitude digital micro-mirror device with the super-pixel encoding technique. The phase profiles of the generated GPOVs are retrieved experimentally through self-built interferometry and exhibit good agreement with the simulations. We also derive a properly modified formula to yield the intensity-uniform GPOVs along predesigned curves, which might find applications in optical tweezers and communications. [ABSTRACT FROM AUTHOR]

Up to now, Gaussian optical vortices (OVs) were investigated with the finite topological charge (TC). Here, we study an OV with the infinite TC. Such OVs have a countable number of phase singularities (isolated intensity nulls), which typically have the unitary TC and are located either equidistantly or not equidistantly on a straight line in the beam transverse cross section. Such OVs are structurally stable (form-invariant) and their transverse intensity is conserved on propagation, changing only in scale and rotation. Orbital angular momentum (OAM) of such OVs is finite, since only a finite number of screw dislocations are within the Gaussian beam in the area of notable intensity, whereas the other phase singularities are in the periphery (and in the infinity), where the intensity is very small. Increasing the Gaussian beam waist radius leads to the parabolic growth of the OAM of such beams. A unique feature of these beams is that their normalized OAM can be adjusted (both increased and decreased) by simple change of the waist radius of the Gaussian beam. In addition to the two form-invariant beams, we studied a Gaussian beam with a countable number of edge dislocations (zero-intensity lines), which is not form-invariant, but, after an astigmatic transform by a cylindrical lens, also becomes an infinite-topological-charge beam. [ABSTRACT FROM AUTHOR]

The terahertz (THz) vortex beam generators are designed and theoretically investigated based on single-layer ultra-thin transmission metasurfaces. Noncontinuous phase changes of metasurfaces are obtained by utilizing Pancharatnam–Berry phase elements, which possess different rotation angles and are arranged on two concentric rings centered on the origin. The circularly polarized incident THz beam could be turned into a cross-polarization transmission wave, and the orbital angular momentum (OAM) varies in value by lℏ. The l values change from ± 1 to ± 5, and the maximal cross-polarization conversion efficiency that could be achieved is 23%, which nearly reaches the theoretical limit of a single-layer structure. The frequency range of the designed vortex generator is from 1.2 THz to 1.9 THz, and the generated THz vortex beam could keep a high fidelity in the operating bandwidth. The propagation behavior of the emerged THz vortex beam is analyzed in detail. Our work offers a novel way of designing ultra-thin and single-layer vortex beam generators, which have low process complexity, high conversion efficiency and broad bandwidth. [ABSTRACT FROM AUTHOR]

We theoretically investigate how the orbital angular momentum of light can affect a chiral magnetic order. Here, we consider a metallic chiral helimagnet, which is under stationary radiation of a resonant optical vortex beam. We propose a novel interaction between local spins considering microscopic interactions between an optical vortex and electrons. This vortex-induced interaction modulates the chiral magnetic order in an entirely different way than an external magnetic field does. Our spin modulation technique may pave a route to create a unique topological or chiral structure for future opto-spintronics devices. [ABSTRACT FROM AUTHOR]

In this paper, for the first time, the concept, analysis and equivalent circuit of a phoenix graphene patch (PGP) unit cell is presented. It is shown that a full 360° phase range can be realized by this unit cell, unlike common graphene patch unit cells, by only separately changing the physical or electrical parameters. Then, a reflectarray antenna based on the PGP cell is designed. The required phases are easily realized by only changing the element dimensions in the cell. The gain and radiation efficiency of the designed antenna are 26 dBi and 75%, respectively. Finally, a programmable vortex beam reflectarray is proposed, whereby the required phases are realized only by the chemical potential of the graphene sheet. The structure is discretized to five sections in the radial direction and eight sections in the azimuth direction. In comparison to other structures, the proposed design can easily generate different vortex beams in real-time by changing the biasing voltages of these sections. [ABSTRACT FROM AUTHOR]

Our research concerns the problem of constructing multiple-twisted spiral beams and the geometry of their fine structure. We analyzed the distribution of energy flows in triangular spiral beams and critical points' positions responsible for their structural stability. It was shown experimentally that a three-spot beam propagates without breaking the internal structure, while the intricate framing of a multiple-twisted triangular beam is distorted beyond the Rayleigh length. We associate such a structural violation with the imperfection of the holographic grating in the spatial light modulator. [ABSTRACT FROM AUTHOR]

Complex vector modes have become topical of late due to their fascinating properties and the many applications they have found across a broad variety of research fields. Even though such modes can be generated in a wide variety of ways, digital holography stands out as one of the most flexible and versatile. Along this line, digital micromirror devices (DMDs) have gained popularity in recent times due to their high refresh rates, which allows the generation of vector modes at kHz rates. Nonetheless, most techniques are limited either by the diversity of vector modes that can be generated or by the speed at which they can be switched. Here we propose a technique based on the concept of random encoding, which allows the generation of arbitrary vector beams at speeds limited only by the refresh rate of the DMD. Our technique will be of great relevance in research fields such as optical communications, laser material processing and optical manipulation, amongst others. [ABSTRACT FROM AUTHOR]

We analytically and numerically study the local dynamical characteristics of the Bessel beams reflected from an air—glass interface near the Brewster angle. A Taylor series expansion based on the angular spectrum component is applied to correct the reflection coefficients near the Brewster angle. Using a hybrid angular spectrum representation and vector potential method, the explicit expressions for the electric and magnetic field components of the reflected Bessel beams are derived analytically under paraxial approximation. The local energy, momentum, spin, and orbital angular momentum of the Bessel beams upon reflection near the Brewster angle are examined numerically by utilizing a canonical approach. Numerical simulation results show that the properties of these dynamical quantities for the Bessel beams near Brewster angle incidence change abruptly, and are significantly affected by their topological charge, half-cone angle, and polarization state. The present study has its importance in understanding the dynamical aspects of optical beams with vortex structure and diffraction-free nature during the reflection process. [ABSTRACT FROM AUTHOR]

A major puzzle of condensed-matter physics is the physics behind the linear-in-temperature law of resistivity in many exotic metallic systems, including cuprates, pnictides, and heavy fermions. In this work, we propose, based on a symmetry-breaking analysis, that the strange metal phase is a novel emergent mesoscopic quantum state, beyond Landau's quasiparticle excitation, which is composed of fluctuating vortices. The model predicts, in a straightforward way, the local magnetic field with a correlation time determined by the Coulomb potential, validated by observations of dynamic muon spin relaxation rates in both 3d cuprates and 5d iridate without fitting parameter. Furthermore, the model resolves the underlying quantum mechanism of the Planckian dissipation in terms of carrier scattering by fluctuating vortex, which predicts a scattering rate proportional to the vortex density, thus deriving both linear-in temperature and linear-in field laws, with a universal scattering coefficient validated by data of several dozens of samples for cuprates and iron pnictides. These findings offer a new phenomenology for non-Fermi liquid in strongly correlated materials. [ABSTRACT FROM AUTHOR]

A wide variety of emission processes by electron wave packets with an orbital angular momentum ℓℏ, called the vortex electrons, can be influenced by a nonparaxial contribution due to their intrinsic electric quadrupole moment. We study Smith–Purcell radiation from a conducting grating generated by a vortex electron, described as a generalized Laguerre–Gaussian packet, which has an intrinsic magnetic dipole moment and an electric quadrupole moment. By using a multipole expansion of the electromagnetic field of such an electron, we employ a generalized surface-current method, applicable for a wide range of parameters. The radiated energy contains contributions from the charge, from the magnetic moment, and from the electric quadrupole moment, as well as from their interference. The quadrupole contribution grows as the packet spreads while propagating, and it is enhanced for large ℓ. In contrast to the linear growth of the radiation intensity from the charge with a number of strips N, the quadrupole contribution reveals an N3 dependence, which puts a limit on the maximal grating length for which the radiation losses stay small. We study spectral-angular distributions of the Smith–Purcell radiation both analytically and numerically and demonstrate that the electron's vorticity can give rise to detectable effects for non-relativistic and moderately relativistic electrons. On a practical side, preparing the incoming electron's state in a form of a non-Gaussian packet with a quadrupole moment—such as the vortex electron, an Airy beam, a Schrödinger cat state, and so on—one can achieve quantum enhancement of the radiation power compared to the classical linear regime. Such an enhancement would be a hallmark of a previously unexplored quantum regime of radiation, in which non-Gaussianity of the packet influences the radiation properties much stronger than the quantum recoil. [ABSTRACT FROM AUTHOR]

It has been demonstrated that metasurfaces have the ability to manipulate the wavefront. However, most multifunctional metasurfaces reported to date only operate in either reflection or transmission mode. In this paper, a bilayer metasurface based on geometric phase is proposed to independently tailor the wavefronts of transmitted and reflected circularly polarized (CP) waves at two different terahertz frequencies. More specifically, the metasurface can transform the incident CP wave to its cross-polarization component with a high conversion coefficient of about 0.87 (0.92) after refraction (reflection) at 0.6 (1.67) THz. The full 2π phase shift can be obtained independently by varying the geometrical parameters of the unit-cell structure at two different operation modes. As proofs of concept, anomalous refraction and reflection, dual-band full-space cylindrical focusing metalens and vortex beam generation with different modes are numerically demonstrated. Our work provides an effective method to integrate two or more different functionalities into a simple metasurface-based device, and the independent phase modulation characteristic of our proposed metasurface also shows infinite potential in wavefront control of full space. [ABSTRACT FROM AUTHOR]

Vector modes represent the most general state of light in which the spatial and polarisation degrees of freedom are coupled in a non-separable way. Crucially, while polarisation is limited to a bi-dimensional space, the spatial degree of freedom can take any spatial profile. However, most generation and application techniques are mainly limited to spatial modes with polar cylindrical symmetry, such as Laguerre– and Bessel–Gauss modes. In this paper we put forward a novel class of vector modes whose spatial degree of freedom is encoded in the helical Mathieu–Gauss beams of the elliptical cylindrical coordinates. We first introduce these modes theoretically and outline their geometric representation on the higher-order Poincaré sphere. Later on, we demonstrate their experimental generation using a polarisation-insensitive technique comprising the use of a digital micromirror device. Finally, we provide a qualitative and a quantitative characterisation of the same using modern approaches based on quantum mechanics tools. It is worth mentioning that non-polar vector beams are highly desirable in various applications, such as optical trapping and optical communications. [ABSTRACT FROM AUTHOR]