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.

Reconfigurable and nonvolatile terahertz lithography-free photonic devices based on phase change films

High-performance terahertz(THz)devices with reconfigurable features are highly desirable in many promising THz applications.However,most of the existing reconfigurable THz elements are still limited to volatile responses,single functionality,and time-consuming multistep manufacturing procedures.In this paper,we report a lithography-free approach to create reconfigurable and nonvolatile THz components by exploring the reversible,nonvolatile,and continuous THz modulation capability of the phase change material Ge_(2)Sb_(2)Te_(5).As a proof of concept,THz gratings with significant Rayleigh anomalies and diffraction as well as ultrathin THz flat lenses with subwavelength and ultra-broadband focusing capabilities are designed and fabricated on ultrathin Ge_(2)Sb_(2)Te_(5)films using the presented photo-imprint strategy.Moreover,such a method can also be adopted to create more complex THz devices,such as Pancharatnam–Berry phase metasurfaces and grayscale holographic plates.With these findings,the proposed method will provide a promising solution to realize reconfigurable and nonvolatile THz elements.

Meta-optics inspired surface plasmon devices

Surface plasmons(SPs)are electromagnetic surface waves that propagate at the interface between a conductor and a dielectric.Due to their unique ability to concentrate light on two-dimensional platforms and produce very high local-field intensity,SPs have rapidly fueled a variety of fundamental advances and practical applications.In parallel,the development of metamaterials and metasurfaces has rapidly revolutionized the design concepts of traditional optical devices,fostering the exciting field of meta-optics.This review focuses on recent progress of meta-optics inspired SP devices,which are implemented by the careful design of subwavelength structures and the arrangement of their spatial distributions.Devices of general interest,including coupling devices,on-chip tailoring devices,and decoupling devices,as well as nascent SP applications empowered by sophisticated usage of meta-optics,are introduced and discussed.

Reflective chiral meta-holography: multiplexing holograms for circularly polarized waves

By allowing almost arbitrary distributions of amplitude and phase of electromagnetic waves to be generated by a layer of sub-wavelength-size unit cells,metasurfaces have given rise to the field of meta-holography.However,holography with circularly polarized waves remains complicated as the achiral building blocks of existing meta-holograms inevitably contribute to holographic images generated by both left-handed and right-handed waves.Here we demonstrate how planar chirality enables the fully independent realization of high-efficiency meta-holograms for one circular polarization or the other.Such circular-polarization-selective meta-holograms are based on chiral building blocks that reflect either left-handed or right-handed circularly polarized waves with an orientation-dependent phase.Using terahertz waves,we experimentally demonstrate that this allows the straightforward design of reflective phase meta-holograms,where the use of alternating structures of opposite handedness yields independent holographic images for circularly polarized waves of opposite handedness with negligible polarization cross-talk.

Layered dissolving microneedles as a need-based delivery system to simultaneously alleviate skin and joint lesions in psoriatic arthritis

Psoriatic arthritis(PsA)is a complicated psoriasis comorbidity with manifestations of psoriatic skin and arthritic joints,and tailoring specific treatment strategies for simultaneously delivering different drugs to different action sites in PsA remains challenging.We developed a need-based layered dissolving microneedle(MN)system loading immunosuppressant tacrolimus(TAC)and antiinflammatory diclofenac(DIC)in different layers of MNs,i.e.,TD-MN,which aims to specifically deliver TAC and DIC to skin and articular cavity,achieving simultaneous alleviation of psoriatic skin and arthritic joint lesions in PsA.In vitro and in vivo skin permeation demonstrated that the inter-layer retained TAC within the skin of~100μm,while the tip-layer delivered DIC up to~300μm into the articular cavity.TD-MN not only efficiently decreased the psoriasis area and severity index scores and recovered the thickened epidermis of imiquimod-induced psoriasis but also alleviated carrageenan/kaolin-induced arthritis even better than DIC injection through reducing joint swelling,muscle atrophy,and cartilage destruction.Importantly,TD-MN significantly inhibited the serum TNF-αand IL-17 A in psoriatic and arthritic rats.The results support that this approach represents a promising alternative to multi-administration of different drugs for comorbidity,providing a convenient and effective strategy for meeting the requirements of PsA treatment.

Terahertz spoof surface-plasmon-polariton subwavelength waveguide

Surface plasmon polaritons(SPPs) with the features of subwavelength confinement and strong enhancements have sparked enormous interest. However, in the terahertz regime, due to the perfect conductivities of most metals, it is hard to realize the strong confinement of SPPs, even though the propagation loss could be sufficiently low. One main approach to circumvent this problem is to exploit spoof SPPs, which are expected to exhibit useful subwavelength confinement and relative low propagation loss at terahertz frequencies. Here we report the design,fabrication, and characterization of terahertz spoof SPP waveguides based on corrugated metal surfaces. The various waveguide components, including a straight waveguide, an S-bend waveguide, a Y-splitter, and a directional coupler, were experimentally demonstrated using scanning near-field terahertz microscopy. The proposed waveguide indeed enables propagation, bending, splitting, and coupling of terahertz SPPs and thus paves a new way for the development of flexible and compact plasmonic circuits operating at terahertz frequencies.

Comparative pharmacokinetics of tetramethylpyrazine phosphate in rat plasma and extracellular fluid of brain after intranasal,intragastric and intravenous administration

The purpose of this study was to compare the pharmacokinetic profiles of tetramethylpyrazine phosphate(TMPP)in plasma and extracellular fluid of the cerebral cortex of rats via three delivery routes:intranasal(i.n.),intragastric(i.g.)and intravenous(i.v.)administration.After i.n.,i.g.and i.v.administration of a single-dose at 10 mg/kg,cerebral cortex dialysates and plasma samples drawn from the carotid artery were collected at timed intervals.The concentration of TMPP in the samples was analyzed by HPLC.The area under the concentration-time curve(AUC)and the ratio of the AUCbrain to the AUCplasma(drug targeting efficiency,DTE)was calculated to evaluate the brain targeting efficiency of the drug via these different routes of administration.After i.n.administration,TMPP was rapidly absorbed to reach its peak plasma concentration within 5 min and showed a delayed uptake into cerebral cortex(t_(max)=15 min).The ratio of the AUCbrain dialysates value between i.n.route and i.v.injection was 0.68,which was greater than that obtained after i.g.administration(0.43).The systemic bioavailability obtained with i.n.administration was greater than that obtained by the i.g.route(86.33%vs.50.39%),whereas the DTE of the nasal route was 78.89%,close to that of oral administration(85.69%).These results indicate that TMPP is rapidly absorbed from the nasal mucosa into the systemic circulation,and then crosses the blood-brain barrier(BBB)to reach the cerebral cortex.Intranasal administration of TMPP could be a promising alternative to intravenous and oral approaches.

Polarization-independent all-silicon dielectric metasurfaces in the terahertz regime

Dielectric metasurfaces have achieved great success in realizing high-efficiency wavefront control in the optical and infrared ranges. Here, we experimentally demonstrate several efficient, polarization-independent, all-silicon dielectric metasurfaces in the terahertz regime. The metasurfaces are composed of cylindrical silicon pillars on a silicon substrate, which can be easily fabricated using etching technology for semiconductors. By locally tailoring the diameter of the pillars, full control over abrupt phase changes can be achieved. To show the controlling ability of the metasurfaces, an anomalous deflector, three Bessel beam generators, and three vortex beam generators are fabricated and characterized. We also show that the proposed metasurfaces can be easily combined to form composite devices with extended functionalities. The proposed controlling method has promising applications in developing low-loss, ultra-compact spatial terahertz modulation devices.

Nonvolatile reconfigurable dynamic Janus metasurfaces in the terahertz regime

Metasurfaces,especially tunable ones,have played a major role in controlling the amplitude,phase,and polarization of electromagnetic waves and attracted growing interest,with a view toward a new generation of miniaturized devices.However,to date,most existing reconfigurable devices are bounded in volatile nature with sustained external energy to maintain and single functionality,which restrict their further applications.Here,we demonstrate for the first time,to our knowledge,nonvolatile,reconfigurable,and dynamic Janus metasurfaces by incorporating phase-change material Ge_(2)Se_(2)Te_(5)(GST)in the terahertz(THz)regime.First,we experimentally show the reversible switching characteristic of GST on large areas by applying a single nanosecond laser pulse,which exhibits excellent contrast of THz properties in both states.Then,we present a multiplex metasurface scheme.In each metasurface,three sets of structures are adopted,in which two sets integrate GST.The effective structures can be reversely modulated by the amorphization and crystallization of GST.As a proof of concept,the dynamic beam splitter,bifocal metalens,dual-mode focusing optical vortex generators,and switchable metalens/focusing optical vortex generators are designed,fabricated,and experimentally characterized,and can be switched reversibly and repeatedly with the help of optical and thermal stimuli.Our scheme will pave the way toward the development of multifunctional and compact THz devices and may find use for applications in THz imaging,sensing,and communications.

Broadband terahertz rotator with an all-dielectric metasurface

Polarization manipulation is essential in developing cutting-edge photonic devices ranging from optical communication displays to solar energy harvesting. Most previous works for efficient polarization control cannot avoid utilizing metallic components that inevitably suffer from large ohmic loss and thus low operational efficiency.Replacing metallic components with Mie resonance-based dielectric resonators will largely suppress the ohmic loss toward high-efficiency metamaterial devices. Here, we propose an efficient approach for broadband, highquality polarization rotation operating in transmission mode with all-dielectric metamaterials in the terahertz regime. By separating the orthogonal polarization components in space, we obtain rotated output waves with a conversion efficiency of 67.5%. The proposed polarization manipulation strategy shows impressive robustness and flexibility in designing metadevices of both linear-and circular-polarization incidences.

All dielectric metasurfaces for spin-dependent terahertz wavefront control

Metasurfaces consisting of artificial subwavelength structure arrays have shown unprecedented ability to manipulate the phase,amplitude,and polarization of light.Separate and complete control over different spin states,namely the orthogonal circular polarizations,has proven more challenging as compared to the control over orthogonal linear polarizations.Here,we present and experimentally demonstrate several spin-dependent wavefront control metasurfaces in the terahertz regime using all-silicon dielectric structures.Such spin-dependent allsilicon metasurfaces are easy to fabricate and have potential applications in spin-involved ultracompact and miniaturized terahertz optical systems as well as terahertz communication systems.

Near-field manipulation of terahertz surface waves by metasurfaces [Invited]

Surface waves(SWs) are a special form of electromagnetic waves that travel along the boundary between a metal and a dielectric. The special optical properties of SWs render them very attractive in applications, such as subdiffractional lithography, novel biochemical sensors, and ultrafast integrated circuitries. Herein, we present a review of our recent progress in excitation and manipulation of terahertz SWs due to interference or coupling between a pair of slit resonators in metasurfaces, showing the ability to devise ultrathin and compact plasmonic components.