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Terahertz (THz) technologies hold great promise for nondestructive precision imaging and wireless communication. Active tailoring of the THz field is highly desired for enhancing the resolution of imaging and increasing communication capacity. However, most THz field manipulation devices are limited by passive modulation and single‐dimensional external triggers. In this study, an innovative spatiotemporally tunable metasurface is proposed for the multidimensional dynamic manipulation of the THz field. The device combines a metasurface and two‐dimensional perovskite materials: the metasurface is responsible for modulation of the THz field in the spatial dimension, while the perovskite is responsible for modulation of the THz field in the temporal dimension. The pumping wavelength is an extra dimension for selectively switching the transmission of the THz field owing to the bandgap tunability of the perovskite. Accordingly, the functions of the metadevice can be multistage‐switched utilizing the pump‐wavelength sensitive control scheme. Based on this platform, dynamic switching of a THz multifocal lens and a dynamic display of holographic characters are experimentally demonstrated. The proposed metasurface provides a new pathway for multiple orders to manipulate the THz field dynamically, which can be used to realize more multifunctional dynamic meta‐devices. [ABSTRACT FROM AUTHOR]

Owing to the fascinating and technologically useful electronic and optical properties, 2D van der Waals (vdW) materials are viewed as the key component for the next‐generation optoelectronic, photovoltaic, and nanoelectronic devices. Fully understanding the ultrafast carrier dynamics in 2D vdW materials is essential to study the fundamental physics and realize potential applications. Time‐resolved terahertz (THz) spectroscopy is a powerful tool used to investigate the ultrafast carrier dynamics and transport properties in semiconducting materials. In recent years, the time‐domain THz spectroscopy measurements, with or without photoexcitation on samples, are widely used to investigate the carrier dynamics of 2D vdW materials. A brief summary on the recent progress of time‐domain THz spectroscopy studies on ultrafast dynamics processes is provided. These include exciton formation and relaxation processes in semiconducting 2D materials, the relaxation of hot electrons in graphene layers, the conductivity of 2D materials modulated by femtosecond laser pulses, and their related physical properties. Finally, the physical properties of 2D vdW materials observed using the time‐domain THz spectroscopy approach are highlighted and the future challenges for time‐resolved THz spectroscopy investigations on 2D vdW materials are presented. [ABSTRACT FROM AUTHOR]

The further development of "lab on fiber" technology demands more powerful optical microsystems and optical fibers with special functions to create sensors with better performance. Whispering gallery microcavities (WGMs) made of different materials with high quality factors show very good sensitivity to gases, nanoparticles, and biocomponents. However, realizing the excitation and detection of the resonant modes of WGMs on the facets of optical fibers is still a great challenge. This work employs the advanced 3D manufacturing technology of two‐photon lithography to fabricate an optical microsystem on the end facet of a multicore optical fiber, which enables excitation and detection of whispering gallery modes on the end facet of an optical fiber. Whispering gallery modes with high quality factors are observed, and the sensing characterization of this device for vapors of three types of volatile organic compounds is investigated. Such optical fiber vapor sensors can be applied in the fields of medical care, environmental monitoring and chemical manufacturing. Additionally, the out‐of‐plane light coupling strategy may be useful for the design of integrated optical circuits on chips. [ABSTRACT FROM AUTHOR]