Plasmonic Vortex Research Articles

Tailoring spatiotemporal dynamics of plasmonic vortices

Plasmonic vortices confining orbital angular momentums to surface have aroused wide research interest in the last decade. Recent advances of near-field microscopes have enabled the study on the spatiotemporal dynamics of plasmonic vortices, providing a better understanding of optical orbital angular momentums in the evanescent wave regime. However, these works only focused on the objective characterization of plasmonic vortex and have not achieved subjectively tailoring of its spatiotemporal dynamics for specific applications. Herein, it is demonstrated that the plasmonic vortices with the same topological charge can be endowed with distinct spatiotemporal dynamics by simply changing the coupler design. Based on a near-field scanning terahertz microscopy, the surface plasmon fields are directly obtained with ultrahigh spatiotemporal resolution, experimentally exhibiting the generation and evolution divergences during the whole lifetime of plasmonic vortices. The proposed strategy is straightforward and universal, which can be readily applied into visible or infrared frequencies, facilitating the development of plasmonic vortex related researches and applications.

Dynamic single microparticle manipulation in the far-field region using plasmonic vortex lens multiple arms with a circular groove.

Recent development of particle manipulation has led to high demand for dynamic optical tweezer structures. However, confining and rotating a single microparticle in the far-field region with a uniform potential distribution remains a complicated task. A plasmonic vortex lens (PVL) has been proven to easily rotate the dielectric particle owing to its effect on orbital angular momentum (OAM). Here we propose and demonstrate PVL multiple arms with a circular groove (CG). The device consists of a multiple arm spiral slit that generates a plasmonic vortex (PV) and a circular groove to bring the PV from the surface to the far-field region. Numerical simulations are performed to calculate the intensity distribution of the primary ring, the optical force and potential. The primary ring size can be adjusted using different polarization directions. PVL 2-arms with a CG has primary ring sizes of 1082 nm under right-handed circular polarization (RCP) and 517 nm under left-handed circular polarization (LCP). Based on these primary ring sizes, a 1 μm polystyrene (PS) bead can be rotated under RCP with a minimum required power of 7.45 mW and trapped under LCP with a minimum required power of 11.84 mW. For PVL 4-arms with a CG under RCP illumination, we optimize the uniform potential distribution by carefully selecting the radius of the groove. Using a groove radius of 1050 nm, we obtain the potential difference between the smallest and largest depth along the x- and y-directions of only 70 k B T/W with a minimum required power of 14.86 mW. The method and design discussed here offer an efficient way to manipulate microparticles for micro-rotors, cell dynamic analysis, etc.

Generation of spatiotemporal optical vortices in ultrashort laser pulses using rotationally interleaved multispirals.

Ultrashort optical vortex pulses carrying spatiotemporal orbital angular momentum (OAM) have inspired versatile applications such as the micromachining of integrated quantum chips and discoveries such as optical toroidal structures and OAM-carrying X-waves. Generating high-quality ultrashort vortices with controllable topological charges remains a crucial issue. Thus, we propose a rotationally interleaved multispiral to generate such vortices. A multispiral comprises multiple identical spirals rotated around the center in the equal-azimuthal interval and interleaved in equal-radius increments; this structure overcomes the previous structural asymmetry of the single spiral and improves the vortex quality. Accordingly, we conducted theoretical analyses, numerical simulations, and experimental investigations that demonstrated the feasibility of multispirals in generating the ultrashort vortices with symmetric distributions and flexibly controlling the topological charges. The proposed study is significant for broader applications involving ultrashort vortices and extensive investigations in related areas such as research on electron vortices, plasmonic vortices, and other matter vortices.

Generation of Tunable Plasmonic Vortices by Varying Wavelength of Incident Light

Surfaces plasmon polaritons carrying orbital angular momentum (OAM), known as plasmonic vortex, hold potential applications for on-chip information multiplexing. However, a traditional plasmonic vortex lens was usually designed for monochromatic incident light and encountered challenges in generating multiple vortices. Here, we demonstrated a wavelength-tunable plasmonic vortex generator that ameliorates these limits, relying on the simultaneous design of a geometric metasurface on an Archimedean spiral. Through this design strategy, both the topological charges and the location of vortices can be controlled with different wavelengths of incident beams. This design and concept can preserve incident wavelength information and can be further applied to integrated and high-dimensional on-chip devices.

On‐Chip Plasmonic Vortex Interferometers (Laser Photonics Rev. 16(10)/2022)

Optical Interferometers In article number 2200242, Yuan-Hao Lang, Quan Xu, and colleagues have developed a new form of optical interferometers by customizing the plasmonic vortex generation from two spin channels. In several square wavelengths, plasmonic vortex interferometer constructs interference field with subwavelength fine structure, demonstrating the measurement of polarization state, spin, and orbital angular momentum of the incident light beam.

On‐Chip Plasmonic Vortex Interferometers

AbstractSince the late 19th century, enormous endeavors have been made in extending the scope and capability of optical interferometers. Recently, plasmonic vortices that strongly confine the orbital angular momentum to surface have attracted considerable attention. However, current research interests in this area have focused on the mechanisms and dynamics of polarization‐dependent single plasmonic vortex generation and evolution, while the interference between different plasmonic vortices for practical applications has been unexplored. Here, a method for flexible on‐chip spin‐to‐orbital angular momentum conversion is introduced, resulting in exotic interferograms. Based on this method, a new form of interferometers that is realized by the interference between customized plasmonic vortices is demonstrated. Within wavelength‐scale dimension, the proposed plasmonic vortex interferometers exhibit superior performance to directly measure the polarization state, spin and orbital angular momentum of incident beams. The proposed interferometry is straightforward and robust, and can be expected to be applied to different scenarios, fueling fundamental advances and applications alike.

Plasmonic vortices: a review

Surface plasmon polaritons (SPPs), surface electromagnetic waves propagating along metal-dielectric interfaces, have found numerous applications in integrated photonic devices, optical storage, and optical sensing, etc. In recent years, there has been a surge of interest in the fundamental and applications of SPPs carrying orbital angular momentum, namely SPP vortices or plasmonic vortices. In this review, we summarize the fundamental concepts of plasmonic vortices, and highlight recent advances in the generation and applications of plasmonic vortices, from SPPs at lightwave frequencies to spoof SPPs at microwave and Terahertz frequencies.

Interactions between Plasmonic Nanoantennas and Vortex Beams.

The orbital angular momentum (OAM) of light offers a new degree of freedom for light-matter interactions, yet how to control such interactions with this physical dimension remains open. Here, by developing a numerical method enabling optical OAM simulations, we provide insights into complex plasmon behaviors with the physical dimension of OAM, and we prove in theory that plasmonic nanostructures can function as efficient antennas to intercept and directionally reradiate the power of OAM beams. The interplay between optical OAM and spin angular momentum (SAM) generates novel particle polarizations and radiations, which were inaccessible before. For arrayed nanoparticles, coherent surface plasmons with specific phase retardations determined by OAM of the beams enable directional power radiations, making a phased array antenna. These findings expand our knowledge of nanoplasmonics in the OAM area and are promising for quantum information processing and dynamic sensing of ultraweak biosignals.

Ultrafast microscopy of a twisted plasmonic spin skyrmion

We report a transient plasmonic spin skyrmion topological quasiparticle within surface plasmon polariton vortices, which is described by analytical modeling and imaging of its formation by ultrafast interferometric time-resolved photoemission electron microscopy. Our model finds a twisted skyrmion spin texture on the vacuum side of a metal/vacuum interface and its integral opposite counterpart in the metal side. The skyrmion pair forming a hedgehog texture is associated with co-gyrating anti-parallel electric and magnetic fields, which form intense pseudoscalar E·B focus that breaks the local time-reversal symmetry and can drive magnetoelectric responses of interest to the axion physics. Through nonlinear two-photon photoemission, we record attosecond precision images of the plasmonic vectorial vortex field evolution with nanometer spatial and femtosecond temporal (nanofemto) resolution, from which we derive the twisted plasmonic spin skyrmion topological textures, their boundary, and topological charges; the modeling and experimental measurements establish a quantized integer photonic topological charge that is stable over the optical generation pulse envelope.

Gold nanolens for chiral single molecule spectroscopy

High demand for techniques to study molecular chirality inspires us to develop a nanolens for light with orbital angular momentum (OAM). The proposed nanolens can efficiently focus light with OAM onto the nanoscale, and create a so-called plasmonic vortex, which is much smaller than the diffraction limited vortex focused by an ordinary lens. The generated plasmonic vortex can efficiently differentiate between left- and right-handed molecules and probe electronic dipole-forbidden transitions. The nanolens consists of several radially aligned rods, and exploits surface plasmons to generate a plasmonic vortex-like structure in the center. We optimize this design to be suitable for beams with various topological charges, and to be easy to manufacture for the visible wavelengths range. We prove that nanolens can work efficiently with both even and odd number of rods. We study the efficiency of the nanolens for both left- and right-handed light, and show the resultant electric field and phase distributions.

Generation of Tunable Plasmonic Vortices by Varying Wavelength of Incident Light

Generation of Tunable Plasmonic Vortices by Varying Wavelength of Incident Light

A topological lattice of plasmonic merons

Topology is an intrinsic property of the orbital symmetry and elemental spin–orbit interaction, but also, intriguingly, designed vectorial optical fields can break existing symmetries, to impose (dress) topology through coherent interactions with trivial materials. Through photonic spin–orbit interaction, light can transiently turn on topological interactions, such as chiral chemistry, or induce non-Abelian physics in matter. Employing electromagnetic simulations and ultrafast, time-resolved photoemission electron microscopy, we describe the geometric transformation of a normally incident plane wave circularly polarized light carrying a defined spin into surface plasmon polariton field carrying orbital angular momentum which converges into an array of plasmonic vortices with defined spin textures. Numerical simulations show how within each vortex domain, the photonic spin–orbit interaction molds the plasmonic orbital angular momentum into quantum chiral spin angular momentum textures resembling those of a magnetic meron quasiparticles. We experimentally examine the dynamics of such meron plasmonic spin texture lattice by recording the ultrafast nanofemto plasmonic field evolution with deep subwavelength resolution and sub-optical cycle time accuracy from which we extract the linear polarization, L-line singularity distribution, that defines the periodic lattice boundaries. Our results reveal how vectorial optical fields can impress their topologically nontrivial spin textures by coherent dressing or chiral excitations of matter.

Phyllotaxis-inspired nanosieves with multiplexed orbital angular momentum

Nanophotonic platforms such as metasurfaces, achieving arbitrary phase profiles within ultrathin thickness, emerge as miniaturized, ultracompact and kaleidoscopic optical vortex generators. However, it is often required to segment or interleave independent sub-array metasurfaces to multiplex optical vortices in a single nano-device, which in turn affects the device’s compactness and channel capacity. Here, inspired by phyllotaxis patterns in pine cones and sunflowers, we theoretically prove and experimentally report that multiple optical vortices can be produced in a single compact phyllotaxis nanosieve, both in free space and on a chip, where one meta-atom may contribute to many vortices simultaneously. The time-resolved dynamics of on-chip interference wavefronts between multiple plasmonic vortices was revealed by ultrafast time-resolved photoemission electron microscopy. Our nature-inspired optical vortex generator would facilitate various vortex-related optical applications, including structured wavefront shaping, free-space and plasmonic vortices, and high-capacity information metaphotonics.

Plasmonic vortex cavities multiply OAM

Nanooptics Orbital angular momentum (OAM) of light can be confined to metal surfaces in the form of plasmonic vortices, where nanoscale twisted light oscillates together with the free electrons in metal. Spektor et al. introduced the reflection from structural boundaries as a new degree of freedom to generate and control this surface-confined angular momentum. They designed vortex cavities with chiral boundaries, in which subsequent reflections increased the vortex OAM by multiples of the chiral cavity order. They then tracked the spatiotemporal dynamics of the plasmon pulse trains within the vortex cavities using time-resolved photoemission electron microscopy with sub-femtosecond resolution. These results may have applications in quantum initialization schemes and potentially achieve vortex lattice cavities with dynamically evolving topology. Sci.Adv. 10.1126/sciadv.abg5571 (2021).

Orbital angular momentum multiplication in plasmonic vortex cavities.

Orbital angular momentum of light is a core feature in photonics. Its confinement to surfaces using plasmonics has unlocked many phenomena and potential applications. Here, we introduce the reflection from structural boundaries as a new degree of freedom to generate and control plasmonic orbital angular momentum. We experimentally demonstrate plasmonic vortex cavities, generating a succession of vortex pulses with increasing topological charge as a function of time. We track the spatiotemporal dynamics of these angularly decelerating plasmon pulse train within the cavities for over 300 femtoseconds using time-resolved photoemission electron microscopy, showing that the angular momentum grows by multiples of the chiral order of the cavity. The introduction of this degree of freedom to tame orbital angular momentum delivered by plasmonic vortices could miniaturize pump probe-like quantum initialization schemes, increase the torque exerted by plasmonic tweezers, and potentially achieve vortex lattice cavities with dynamically evolving topology.

Demonstration of microwave plasmonic-like vortices with tunable topological charges by a single metaparticle

Light beams with helical wave fronts, also called optical vortices, have attracted great interest in the community of optics and photonics. They provide an additional degree of freedom for light manipulation, leading to wide-ranging potential applications in micro-particle trapping, optical microscopy, and even quantum information processing. Recently, metallic microstructures are introduced to confine the plasmonic vortices into deep subwavelength dimension, which benefits photonic integration on chip. In this Letter, exploiting the excitation of spoof surface plasmon, we experimentally demonstrate the near-field optical vortices with tunable topological charges supported by a single metaparticle in the microwave regime. These microwave plasmonic-like vortices are excited by surface waves with a spatial asymmetric distribution of electromagnetic field, which are launched by a metallic comb-shaped waveguide. Experimental characterization of highly localized and controllable near-field vortices with the nature of deep subwavelength confirms the numerical simulation. In addition, an equivalent physical model based on the coupled mode theory is proposed to understand the generation mechanism of these spoof plasmonic vortices. Our approach offers an efficient way to generate deterministic subwavelength optical vortices, which provides the potential for critical vortex elements on photonic integrated chip.

Bloch-type photonic skyrmions in optical chiral multilayers

Magnetic skyrmions are topological quasiparticles in magnetization. Recently, as one of their photonic counterparts, Néel-type photonic skyrmions were discovered in evanescent electromagnetic waves. The deep-subwavelength features of the photonic skyrmions suggest their potential in optical imaging quantum technologies and data storage. Here, by exploiting the photonic quantum spin Hall effect of a plasmonic vortex in a trilayered structure, we predict the existence of photonic twisted-Néel- and Bloch-type skyrmions in chiral materials. Their chirality-dependent features can be considered as additional degrees of freedom for future chiral sensing, information processing, and storage technologies. In particular, our findings enrich the formations of photonic skyrmions and reveal a remarkable resemblance of the feature of chiral materials in two seemingly distant fields: photonic skyrmions and magnetic skyrmions.2 MoreReceived 16 December 2020Accepted 9 April 2021DOI:https://doi.org/10.1103/PhysRevResearch.3.023109Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasChiralityLight-matter interactionNanophotonicsNear-field opticsPlasmonicsSkyrmionsTopological effects in photonic systemsAtomic, Molecular & Optical

Functional Meta Lenses for Compound Plasmonic Vortex Field Generation and Control.

Surface plasmon polaritons carrying orbital angular momentum are of great fundamental and applied interest. However, common approaches for their generation are restricted to having a weak dependence on the properties of the plasmon-generating illumination, providing a limited degree of control over the amount of delivered orbital angular momentum. Here we experimentally show that by tailoring local and global geometries of vortex generators, a change in helicity of light imposes arbitrary large switching in the delivered plasmonic angular momentum. Using time-resolved photoemission electron microscopy we demonstrate pristine control over the generation and rotation direction of high-order plasmonic vortices. We generalize our approach to create complex topological fields and exemplify it by studying and controlling a "bright vortex", exhibiting the breakdown of a high-order vortex into a mosaic of unity-order vortices while maintaining the overall angular momentum density. Our results provide tools for plasmonic manipulation and could be utilized in lab-on-a-chip devices.

High order plasmonic vortex generation based on spiral nanoslits

Highly localized plasmonic vortices carrying orbital angular momentum are of importance for many applications. Yet, it is a challenge to generating plasmonic vortex with a high topological charge because of no available technique. Here, a novel plasmonic vortex generator is proposed based on spiral nanoslits etched in a metal film, which can produce a high order plasmonic vortex. The consecutive spiral nanoslit can generate plasmonic vortex with high intensity and the segmented nanoslits enhances the controllability of the plasmonic vortex, which are demonstrated numerically and experimentally. High order plasmonic vortex generation will broaden the prospects for plasmonic vortices in practical applications for nanomanipulation and nanofabrication.

Localized Plasmonic Vortex Printing Technology Based on the Metaparticle and Spoof Surface Plasmon Polaritons

Plasmonic structures based on Archimedes spiral (AS) architectures have attracted great interest to generate plasmonic vortices (PVs) carrying controllable orbital angular momentum (OAM). Recently, researches based on the single deep‐subwavelength metaparticle have provided various methods to realize PVs. However, most of the PVs structures just realize single topological charge and only a few works have implemented vortex waves with multiple topological charges. Hence, it is still a big challenge to excite localized electromagnetic (EM) vortices with multimodal topological charges in single structure simultaneously. A potential design idea to create localized EM vortices with multimodal topological charges in single structure is proposed, which is called the printing technology for localized PVs. Taking advantages of the coplanar waveguide‐based spoof surface plasmon polaritons (CPW‐based SSPPs), localized multiple PVs modes that are strongly confined in the metaparticles can be excited simultaneously. The physical explanations and experiments are conducted to confirm this unique phenomenon. This localized PVs printing technology may be used for future microwave integrated elements and devices operating.