With the rapid development of terahertz technology, tunable high-efficiency broadband functional devices have become a research trend. In this research, a dynamically tunable dual broadband terahertz absorber based on the metamaterial structure of vanadium dioxide (VO₂) is proposed and analyzed. The metamaterial is composed of patterned VO₂ on the top layer, gold on the bottom layer and silicon dioxide (SiO₂) as the middle dielectric layer. Simulation results show that two bandwidths of 90% absorption reach as wide as 2.32 THz from 1.87 to 4.19 THz and 2.03 THz from 8.70 to 10.73 THz under normal incidence. By changing the conductivity of VO₂, the absorptance dynamically tuned from 2% to 94%. Moreover, it is verified that absorptance is insensitive to the polarization angle. The physical origin of this absorber is revealed through interference theory and matching impedance theory. We further investigate the physical mechanism of dual broadband absorption through electric field analysis. This design has potential applications in imaging, modulation and stealth technology.

We use a single-layer thick metallic metasurface to design the 0-,45- and 90-degree polarizers with transmission efficiencies exceeding 95% based on the bright electric dipole resonance and dark magnetic dipole resonance. In addition, we utilize a bilayer metallic metasurface (forming an efficient Fabry-Perot resonator) to propose a circularly polarizing dichroism waveplate (CPDW). The circular polarization dichroism (CPD = I _RCP − I _LCP .) in the transmission mode at 1.6 µm wavelength reaches 89% and the extinction ratio (ER = I _RCP /I _LCP ) is 830:1. These four polarizing elements are integrated to form a full Stokes pixel that almost accurately measures arbitrary polarized light at λ₀ = 1.6 µm (including elliptically polarized light).

The solar wind plays important roles on terrestrial magnetosphere dynamics, including the particle population and plasma waves generation. Here we report an interesting event that ULF waves are enhanced right after solar wind compression and the compressional mode ULF wave subsequently modulates both the intensity and energy flux direction of whistler-mode waves. Quasi-periodic whistler-mode wave packets are observed around L=5.6 at noon sector by Van Allen Probes. Growth rate calculation demonstrates that the compressional mode ULF wave can modulate the whistler-mode wave intensity by modulating the energetic electron anisotropy. Moreover, the direction of wave energy flux is observed to alternate between northward and southward at equator, which is probably because the intense ULF waves periodically alter the relative direction of the wave source region respect to the spacecraft. The current results provide a chain of observational evidences to illustrate how the generation and propagation of whistler-mode waves in the inner magnetosphere are affected by ULF waves during the solar wind dynamic pressure enhancement.

Magnetosonic (MS) waves are generally considered as electromagnetic harmonic fluctuations below the lower hybrid frequency. Here we present a correlated observation of proton ring‐like distribution and low harmonic magnetosonic waves with undetectable magnetic components (called QEMS). We conduct fully thermal simulations (WHAMP) to investigate the wave properties. The calculated growth rates can reproduce the observed spectral characteristics and demonstrate that the QEMS waves are excited as ion Bernstein modes by proton ring‐like distribution. The ratios between the wave electric and magnetic amplitudes E/B given by WHAMP indicate that the magnetic spectral densities are below the instrument noise level, and the ratios are ∼7–80 times larger than the wave phase speeds V_ph, suggesting that the QEMS waves are essentially quasi‐electrostatic, not just visually quasi‐electrostatic due to the measurement limit. This study provides further insights into the QEMS natures.

The optical vortex (OV) has drawn considerable attention owing to its tremendous advanced applications, such as optical communication, quantum entanglement, and on-chip detectors. However, traditional OV generators suffer from a bulky configuration and limited performance, especially in the ultraviolet range. In this paper, we utilize a large bandgap dielectric material, niobium pentoxide (Nb₂O₅), to construct ultra-thin and compact transmission-type metasurfaces to generate and detect the OV at a wavelength of 355 nm. The meta-atom, which operates as a miniature half-wave plate and demonstrates a large tolerance to fabrication error, manipulates the phase of an incident right-handed circular polarized wave with high cross-polarized conversion efficiency (around 86.9%). The phase delay of $\pi$ between the orthogonal electric field component is attributed to the anti-parallel magnetic dipoles induced in the nanobar. Besides, focused vortex generation (topological charge l from 1 to 3) and multichannel detection (l from −2 to 2) are demonstrated with high efficiency, up to 79.2%. We envision that our devices of high flexibility may have potential applications in high-performance micron-scale integrated ultraviolet nanophotonics and meta-optics.

Whistler mode chorus waves play an important role in the radiation belt dynamics, which usually appear as discrete elements with frequency sweeping. Finer structure analysis shows that a chorus element is composed of several frequency‐sweeping subelements, and such two‐level structures can be successfully reproduced by modeling based on nonlinear theories. Previous observations and models suggest that an element and its subelements should have the same frequency‐sweep direction. However, we here present two unexpected chorus rising tone events within which the subelements exhibit clearly reversed, falling frequency‐sweep. Moreover, the subelements consist of several wave packets that also show falling frequency‐sweep features. The three‐level structured chorus elements are distinctly different from all the reported observations and seem to bring challenges to the existing theories. We propose a possible scenario that the falling tone subelements are formed by nonlinear process with much shorter timescale and the starting frequency of each subelement is controlled by fast varying electron distribution. This study may inspire more studies toward a thorough understanding of the chorus generation process.