All‐inorganic perovskite nanocrystals (NCs) have attracted considerable attention due to their extensive photonic and optoelectronic properties. These NCs are shown to exhibit strong multiphoton absorption (MPA). However, studies on the MPA properties of perovskite NCs are only conducted on weakly confined perovskite cubic NCs, while the relevant influences of the geometry are never discussed. To the best of knowledge, this report describes the first comparison of the MPA properties of CsPbBr3 2D nanoplates (2D NPs) and cubic NCs. Based on the experimental results, it can be concluded that stronger quantum confinement effect of 2D NPs will strongly enhance their MPA with outstanding normalized‐volume two‐ and three‐photon absorption cross sections up to 1561 GM nm−3 and 7.2 × 10−78 cm6 s2 photon−2 nm−3, respectively. This work demonstrates that CsPbBr3 2D NPs are good candidates for exploring the influences of quantum confinement on MPA properties of perovskite NCs, which are also highly suitable for the applications of multiphoton imaging and nonlinear optoelectronics.

The use of microwave (MW) irradiation to increase the rate of chemical reactions has attracted much attention recently in nearly all fields of chemistry due to substantial enhancements in reaction rates. However, the intrinsic nature of the effects of MW irradiation on chemical reactions remains unclear. Herein, the highly effective conversion of NO and decomposition of H2S via MW catalysis were investigated. The temperature was decreased by several hundred degrees centigrade. Moreover, the apparent activation energy (Ea’) decreased substantially under MW irradiation. Importantly, for the first time, a model of the interactions between microwave electromagnetic waves and molecules is proposed to elucidate the intrinsic reason for the reduction in the Ea’ under MW irradiation, and a formula for the quantitative estimation of the decrease in the Ea’ was determined. MW irradiation energy was partially transformed to reduce the Ea’, and MW irradiation is a new type of power energy for speeding up chemical reactions. The effect of MW irradiation on chemical reactions was determined. Our findings challenge both the classical view of MW irradiation as only a heating method and the controversial MW non-thermal effect and open a promising avenue for the development of novel MW catalytic reaction technology.

No abstract

A high-sensitivity temperature sensor based on the enhanced Goos-Hänchen effect in a symmetrical metal-cladding waveguide is theoretically proposed and experimentally demonstrated. Owing to the high sensitivity of the ultrahigh-order modes, any minute variation of the refractive index and thickness in the guiding layer induced by the thermo-optic and thermal expansion effects will easily give rise to a dramatic change in the position of the reflected light. In our experiment, a series of Goos-Hänchen shifts are measured at temperatures varying from 50.0 °C to 51.2 °C with a step of 0.2 °C. The sensor exhibits a good linearity and a high resolution of approximately 5×10(-3) °C. Moreover, there is no need to employ any complicated optical equipment and servo techniques, since our transduction scheme is irrelevant to the light source fluctuation.

No abstract

Non-diffraction guiding modes covering the full broad band of a photonic crystal with elliptical rods for TM mode are reported in this paper. All such modes can be used to effectively guide electromagnetic waves since they have near-zero group velocity components along the X direction. In the fourth dispersion surface of the photonic crystal, the two wide flat regions spanning the first Brillouin zone possess unique properties: one dimension corresponds to a broad band, while the other corresponds to full incident angles of 0-90 •. These properties have many potential applications; as an example, here a broadband all-angle supercollimation with a bandwidth of 169 nm around 1550 nm is demonstrated. For the inverted structure of elliptical holes in a dielectric, similar results can be achieved over 140 nm around 1550 nm for TE mode.

In this paper, we propose an aerial reconfigurable intelligent surface (RIS) system to support the stringent constraints of ultra-reliable low latency communication (URLLC). Specifically, unmanned aerial vehicles (UAVs) employed onboard RIS panels can act as repeaters to reflect the signal from macro base station (MBS) to all users in the networks. To overcome the dense networks' interference, we propose to use zero-forcing beamforming and time division multiplexing access (TDMA) scheme where each UAV can serve a number of users in its own cluster. We formulate a optimisation framework in terms of UAVs' deployment, power allocation at MBS, phase-shift of RIS, and blocklength of URLLC. Due to highly nonconvex and complex optimisation problem, we first consider to use a deep neural network (DNN) to solve the optimal UAVs' deployment. Then, the optimal resource allocation is proposed to provide the maximal reliability of the considered system with respect to the users' fairness. From the representative numerical results, our proposed scheme is shown to superior to other benchmarks which exhibits the positive impact of aerial RIS in supporting stringent demands of URLLC.INDEX TERMS Ultra-reliable low-latency communications (URLLC), Reconfigurable Intelligent Surface (RIS), Unmanned aerial vehicle (UAV).

No abstract