Artificially designed modulators that enable a wealth of freedom in manipulating the terahertz (THz) waves at will are an essential component in THz sources and their widespread applications. Dynamically controlled metasurfaces, being multifunctional, ultrafast, integrable, broadband, high contrasting, and scalable on the operating wavelength, are critical in developing state-of-the-art THz modulators. Recently, external stimuli-triggered THz metasurfaces integrated with functional media have been extensively explored. The vanadium dioxide (VO₂)-based hybrid metasurfaces, as a unique path toward active meta-devices, feature an insulator–metal phase transition under the excitation of heat, electricity, and light, etc. During the phase transition, the optical and electrical properties of the VO₂ film undergo a massive modification with either a boosted or dropped conductivity by more than four orders of magnitude. Being benefited from the phase transition effect, the electromagnetic response of the VO₂-based metasufaces can be actively controlled by applying external excitation. In this review, we present recent advances in dynamically controlled THz metasurfaces exploiting the VO₂ phase transition categorized according to the external stimuli. THz time-domain spectroscopy is introduced as an indispensable platform in the studies of functional VO₂ films. In each type of external excitation, four design strategies are employed to realize external stimuli-triggered VO₂-based THz metasurfaces, including switching the transreflective operation mode, controlling the dielectric environment of metallic microstructures, tailoring the equivalent resonant microstructures, and modifying the electromagnetic properties of the VO₂ unit cells. The microstructures’ design and electromagnetic responses of the resulting active metasurfaces have been systematically demonstrated, with a particular focus on the critical role of the VO₂ films in the dynamic modulation processes.

Directionally scattered surface plasmon polaritons (SPPs) promote the efficiency of plasmonic devices by limiting the energy within a given spatial domain, which is one of the key issues to plasmonic devices. Benefitting from the magnetic response induced in high-index dielectric nanoparticles, unidirectionally scattered SPPs have been achieved via interference between electric and magnetic resonances excited in the particles. Yet, as the magnetic response in low-index dielectric nanoparticles is too weak, the directionally scattered SPPs are hard to detect. In this work, we demonstrate forward scattered SPPs in single low-index polystyrene (PS) nanospheres. We numerically illustrate the excitation mechanism of plasmonic induced electric and magnetic multipole modes, as well as their contributions to forward SPP scattering of single PS nanospheres. We also simulate the SPP scattering field distribution obtaining a forward-to-backward scattering intensity ratio of 50.26:1 with 1 μm PS particle. Then the forward scattered SPPs are experimentally visualized by Fourier transforming the real-space plasmonic imaging to k-space imaging. The forward scattered SPPs from low-index dielectric nanoparticles pave the way for SPP direction manipulation by all types of nanomaterials.

Due to their excellent physical and chemical properties, graphene sheets are widely used in industry, which makes detection important to guarantee their performance. Atomic force microscopy, scanning electron microscopy, and Raman spectroscopy are the most common detection methods, which is either time-consuming or easily destructive. In this work, we presented a fast and nondestructive method to detect single graphene sheets by using plasmonic imaging. Dual channel sampling plasmonic imaging combining the image processing algorithm is used to improve the deterioration from propagation length of surface plasmon polaritons and reconstruct the complete morphology of single graphene sheets. The fast and nondestructive detection method paves the way to applications of graphene, and can be extended to the detections of two-dimensional materials, single biological molecule, viruses, and nanomaterials.

In this erratum, the function λ S P P in the third page of Opt. Lett. 44, 5707 (2019)OPLEDP 0146-9592 10.1364/OL.44.005707 has been corrected.

We present systematic experimental studies of the impact of subwavelength structural geometries and electromagnetic field polarization on the resonance behavior of metallic metasurfaces at D-band frequencies. The measured influence of the photoconductive receiver antenna design in terahertz time-domain spectroscopy on the frequency-domain spectral features was analyzed. Numerical simulations reveal distinct resonance characteristics in the D-band regime, where extraordinary amplitude transmission is highly dependent on the array dimensions and field polarization orientation. The metasurface enables significant enhancements in surface electric fields and resonance response, attributed to the effective excitation of strong dipolar modes. These results demonstrate the extraordinary transmission capabilities of subwavelength metallic arrays and provide valuable insights for designing compact, low-loss, and tunable terahertz functional components needed in next-generation communications.

We present broadband terahertz studies of high-purity single-crystal diamond grown by chemical vapor deposition over a frequency range of 0.2–4.5 THz. The experimentally characterized conductivity exhibits a pronounced non-monotonic frequency dependence that cannot be described by the conventional Drude model. To capture this behavior, we employ a constrained Drude–Lorentz (CDL) model, which incorporates free-carrier transport and an effective off-resonant polarization contribution beyond the measured spectral window. The real part of the dielectric function yields ε1 ≈ 5.64, consistent with the known static dielectric constant of diamond. The CDL model accurately reproduces the broadband response, from which a carrier mobility of ∼2963 cm2/V s and a carrier density of ∼1.05 × 1013 cm−3 are obtained. These results show that the broadband nature of terahertz time-domain spectroscopy is essential for resolving coupled carrier–polarization dynamics in high-purity diamond.