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.

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 Ge2Sb2Te5. 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 Ge2Sb2Te5 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.

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 Ge2Se2Te5 (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.

Metamaterials composed of metallic antennae arrays are used as they possess extraordinary optical transmission (EOT) in the terahertz (THz) region, whereby a giant forward light propagation can be created using constructive interference of tunneling surface plasmonic waves. However, numerous applications of THz meta-devices demand an active manipulation of the THz beam in free space. Although some studies have been carried out to control the EOT for the THz region, few of these are based upon electrical modulation of the EOT phenomenon, and novel strategies are required for actively and dynamically reconfigurable EOT meta-devices. In this work, we experimentally present that the EOT resonance can be coupled to optically reconfigurable chalcogenide metamaterials which offers a reversible all-optical control of the THz light. A modulation efficiency of 88% in transmission at 0.85 THz is experimentally observed using the EOT metamaterials, which is composed of a gold (Au) circular aperture array sitting on a non-volatile chalcogenide phase change material (Ge₂Sb₂Te₅) film. This comes up with a robust and ultrafast reconfigurable EOT over 20 times of switching, excited by a nanosecond pulsed laser. The measured data have a good agreement with finite-element-method numerical simulation. This work promises THz modulators with significant on/off ratios and fast speeds.Metamaterials composed of metallic antennae arrays are used as they possess extraordinary optical transmission (EOT) in the terahertz (THz) region, whereby a giant forward light propagation can be created using constructive interference of tunneling surface plasmonic waves. However, numerous applications of THz meta-devices demand an active manipulation of the THz beam in free space. Although some studies have been carried out to control the EOT for the THz region, few of these are based upon electrical modulation of the EOT phenomenon, and novel strategies are required for actively and dynamically reconfigurable EOT meta-devices. In this work, we experimentally present that the EOT resonance can be coupled to optically reconfigurable chalcogenide metamaterials which offers a reversible all-optical control of the THz light. A modulation efficiency of 88% in transmission at 0.85 THz is experimentally observed using the EOT metamaterials, which is composed of a gold (Au) circular aperture array sitting on a non-volatile chalcogenide phase change material (Ge₂Sb₂Te₅) film. This comes up with a robust and ultrafast reconfigurable EOT over 20 times of switching, excited by a nanosecond pulsed laser. The measured data have a good agreement with finite-element-method numerical simulation. This work promises THz modulators with significant on/off ratios and fast speeds.

Radiation at terahertz frequencies can be used to analyze the structural dynamics of water and biomolecules, but applying the technique to aqueous solutions and tissues remains challenging since terahertz radiation is strongly absorbed by water. While this absorption enables certain analyses, such as the structure of water and its interactions with biological solutes, it limits the thickness of samples that can be analyzed, and it drowns out weaker signals from biomolecules of interest. We present a method for analyzing water-rich samples via time-domain terahertz optoacoustics over a 10⁴-fold thickness ranging from microns to centimeters. We demonstrate that adjusting the temperature to alter the terahertz optoacoustic (THz-OA) signal of water improves the sensitivity with which it can be analyzed and, conversely, can reduce or even “silence” its signal. Temperature-manipulated THz-OA signals of aqueous solutions allow detection of solutes such as ions with an order of magnitude greater sensitivity than terahertz time-domain spectroscopy, and potentially provide more characteristic parameters related to both terahertz absorption and ultrasonic propagation. Terahertz optoacoustics may be a powerful tool for spectroscopy and potential imaging of aqueous solutions and tissues to explore molecular interactions and biochemical processes.