Experimental demonstration of ultra-large-scale terahertz all-dielectric metamaterials

All-dielectric metamaterials have emerged as a promising platform for low-loss and highly efficient terahertz devices. However, existing fabrication methods have difficulty in achieving a good balance between precision and cost. Here, inspired by the nano-template-assisted self-assembly method, we develop a micro-templateassisted self-assembly(MTAS) method to prepare large-scale, high-precision, and flexible ceramic microsphere all-dielectric metamaterials with an area exceeding 900 cm × 900 cm. Free from organic solvents, vacuum, and complex equipment, the MTAS method ensures low-cost and environmentally friendly fabrication. The ceramic microsphere resonators can be readily assembled into nearly arbitrary arrangements and complex aggregates, such as dimers, trimers, quadrumers, and chains. Finally, using the heat-shrinkable substrate and dipole coupling effect, a broadband reflector with a bandwidth of 0.15 THz and a reflection of up to 95% is demonstrated.This work provides a versatile and powerful platform for terahertz all-dielectric metamaterials, with potential to be applied in a wide variety of high-efficiency terahertz devices.

Real-time monitoring of hydrogel phase transition in an ultrahigh Q microbubble resonator

The ability to sense dynamic biochemical reactions and material processes is particularly crucial for a wide range of applications,such as early-stage disease diagnosis and biomedicine development.Optical microcavities-based label-free biosensors are renowned for ultrahigh sensitivities,and the detection limit has reached a single nanoparticle/molecule level.In particular,a microbubble resonator combined with an ultrahigh quality factor(Q)and inherent microfluidic channel is an intriguing platform for optical biosensing in an aqueous environment.In this work,an ultrahigh Q microbubble resonator-based sensor is used to characterize dynamic phase transition of a thermosensitive hydrogel.Experimentally,by monitoring resonance wavelength shift and linewidth broadening,we(for the first time to our knowledge)reveal that the refractive index is increased and light scattering is enhanced simultaneously during the hydrogel hydrophobic transition process.The platform demonstrated here paves the way to microfluidical biochemical dynamic detection and can be further adapted to investigating single-molecule kinetics.

A Small-Divergence-Angle Orbital Angular Momentum Metasurface Antenna

Electromagnetic waves carrying an orbital angular momentum (OAM) are of great interest. However, most OAM antennas presentdisadvantages such as a complicated structure, low efficiency, and large divergence angle, which prevents their practicalapplications. So far, there are few papers and research focuses on the problem of the divergence angle. Herein, a metasurfaceantenna is proposed to obtain the OAM beams with a small divergence angle. The circular arrangement and phase gradient wereused to simplify the structure of the metasurface and obtain the small divergence angle, respectively. The proposed metasurfaceantenna presents a high transmission coefficient and effectively decreases the divergence angle of the OAM beam. All thetheoretical analyses and derivation calculations were validated by both simulations and experiments. This compact structurepaves the way to generate OAM beams with a small divergence angle.

A VO_(2) film-based multifunctional metasurface in the terahertz band

We proposed a multifunctional terahertz metasurface based on a double L-shaped pattern and a vanadium dioxide(VO_(2)) film separated by polyimide.When the VO_(2)film is an insulator,a dual-band electromagnetically induced transparency effect is obtained,and the physical mechanism is investigated based on the current distribution and "two-particle" model.When the VO_(2)film is a metal,a dual-band linear-to-circular polarization converter,in which the y-polarized linear wave can be effectively converted to left-handed circularly polarized(LCP) and right-handed circularly polarized simultaneously in different bands,can be achieved.By arranging the metal pattern rotating 30°,a multifunctional antenna can be obtained.When the VO_(2)is an insulator,the radiation of the LCP wave is divided into four beams,with two beams reflected and two beams transmitted.When the VO_(2)is in the metallic state,we can only get the co-polarized reflected wave with a 21° angle.Moreover,in our design,the VO_(2)film does not need lithography to obtain certain patterns,which improves the convenience of fabrication and experiment.Our design opens a new way for the development of multifunctional terahertz devices and has potential applications in the terahertz communication field.

Anti-Jahn-Teller effect induced ultrafast insulator to metal transition in perovskite BaBiO_(3)

The Jahn-Teller(JT)effect involves the ions M with a degenerate electronic state distorting the corner-sharing MO_(6)octahedra to lift the degeneracy,inducing strong coupling of electrons to lattice,and mediating the exotic properties in perovskite oxides.Conversely,the anti-Jahn–Teller(AJT)effect refers to the deformation against the Jahn-Teller-distorted MO_(6)octahedra.However,it is difficult to experimentally execute both effects descending from the fine-tuning of crystal structures.We propose the AJT can be introduced by THz laser illumination at 11.71 THz in a candidate superconducting perovskite material BaBiO_(3)near room temperature.The illumination coherently drives the infrared-active phonon that excites the Raman breathing mode through the quadratic-linear nonlinear interaction.The process is characterized by the emergence of an AJT effect,accompanied by an insulator-to-metal transition occurring on the picosecond timescale.This study underlines the important role of crystal structure engineering by coherent phonon excitation in designing optoelectronic devices.