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Over the past decade, orbital angular momentum has garnered considerable interest in the field of plasmonics owing to the emergence of surface-confined vortices, known as plasmonic vortices. Significant progress has been made in the generation and manipulation of plasmonic vortices, which broadly unveil the natures of plasmonic spin–orbit coupling and provide accessible means for light–matter interactions. However, traditional characterizations in the frequency domain miss some detailed information on the plasmonic vortex evolution process. Herein, an exotic spin–orbit coupling phenomenon is demonstrated. More specifically, we theoretically investigated and experimentally verified a temporally deuterogenic vortex mode, which can be observed only in the time domain and interferes destructively in the intensity field. The spatiotemporal evolution of this concomitant vortex can be tailored with different designs and incident beams. This work extends the fundamental understanding of plasmonic spin–orbit coupling and provides a unique optical force manipulation strategy, which may fuel plasmonic research and applications in the near future.

With the drafting of the 6G white paper, terahertz (THz) modulators reshow profound significance in wireless communication, data storage, and imaging. Active tuning of THz waves through hybrid meta-structure incorporated with smart materials has attracted keen interest due to the deliberate structural design and dynamic transition of material properties. However, until now, these meta-devices have usually been responsive to a single driving field, such as electrical, thermal, or optical stimuli, which hinders their applicability for multidimensional manipulation of THz waves. Herein, to the best of our knowledge, a Ba0.6Sr0.4TiO3–silicon hybrid meta-modulator to achieve opposite tuning of the amplitude characteristic with two different types of stimuli is proposed for the first time. When driven by an external voltage, the proposed meta-modulator exhibits enhanced transmittance. In contrast, the transmission coefficient gradually decays as the external current increases. This outstanding performance is systematically studied by analyzing the carrier transport in the meta-structure as well as the change in the dielectric constant. Our research provides a novel idea for the development of actively tunable THz meta-devices and paves the way for robust multifunctionality in electrically controlled THz switching, and biosensors.

Cylindrical vector beams (CVBs), being a special kind of beams with spatially variant states of polarizations, are promising in photonics applications, including high-resolution imaging, plasmon excitation, optical trapping, and laser machining. Recently, generating CVBs using metasurfaces has drawn enormous interest owing to their highly designable, multifunctional, and integratable features. However, related studies remain unexplored in the terahertz regime. Here, a generic method for efficiently generating terahertz CVBs carrying orbital angular momentums (OAMs) is proposed and experimentally demonstrated using transmission-type spatial-variant dielectric metasurfaces, which is realized by designing the interference between the two circularly polarized transmission components. This method is based on spin-decoupled phase control allowed by simultaneously manipulating the dynamic phase and geometric phase of each structure, endowing more degree of freedom in designing the vector beams. Two types of metasurfaces which respectively generate polarization-dependent terahertz vector vortex beams (VVBs) and vector Bessel beams (VBBs) are experimentally characterized. The proposed method opens a new window to generate versatile vector beams, providing new capabilities in developing novel, compact, and high-performance devices applicable to broad electromagnetic spectral regimes.

For terahertz (THz) integrated systems, an intersection between waveguides is inevitable and is often accompanied by considerable crosstalk and loss. Here, we propose and experimentally demonstrate a novel type of crossing with a footprint less than 0.2 × 0.2 mm2 for THz surface plasmon polariton waveguiding. With an optimized crossover structure, the measured loss of the intersection is as low as 0.89 dB/crossing, and the crosstalk is less than −19.06 dB/crossing at 0.55 THz. The proposed crossing structure is compact and has low loss and crosstalk within a broad band, which will pave the way for a wide range of new applications for THz integrated systems.

Ion hydration plays a crucial role in numerous fundamental processes. Various spectroscopic methods are employed to investigate the slowing down of hydration bond dynamics in the proximity of both anions and cations. To date, most of these studies have primarily focused on the properties of binary systems. However, in comparison to ion–water binary systems, ternary systems that involve ions, water, and organic matter are more prevalent in nature and provide more realistic insights into biological processes. This study focuses on ion hydration in water and alcohol mixture using terahertz spectroscopy and x-ray diffraction (XRD). The results reveal a distinct behavior depending on the type of alcohol used. Specifically, the presence of both methanol and ethanol results in the disappearance of absorption peaks associated with NaCl hydrate at low temperatures. In contrast, tert-butanol does not exhibit such an effect, and isopropanol demonstrates a more complex response. By combining these terahertz spectroscopic findings with low-temperature XRD data, we gain insights into the formation, or lack thereof, of NaCl · 2H2O hydrate crystals. Crucially, our observations suggest a dominant correlation between the polarity of the alcohol molecules and its impact on the Na+ hydration. Strongly polar alcohols preferentially solvating the Na+ ion lead to the failure of hydrate formation, while weakly polar alcohols do not have this effect. [ABSTRACT FROM AUTHOR]