A moving charged particle, such as an electron, can radiate light due to the interaction between its Coulomb field and surrounding matter. This phenomenon has spawned great interest in the fields of physics, electron microscopy, optics, biology, and materials science. Since the radiation generated by the charged particles strongly depends on the surrounding matter, artificially engineered materials with exotic electromagnetic and optic properties, including metamaterials and metasurfaces, provide an unprecedented opportunity to tailor the interaction between the charged particle and matter, and ultimately enable to manipulate the radiated light. In this review, the fundamentals of Cherenkov radiation and Smith–Purcell radiation are presented. Subsequently, the recent advances in the control of Cherenkov radiation and Smith–Purcell radiation based on metamaterials and metasurfaces are summarized. Finally, the applications using these two physical phenomena, including electron‐driven photon sources and electron accelerators, are discussed in this review.

Graphene, a 2D material with tunable optical properties, has recently attracted intense interest for reconfigurable metasurfaces. So far, the working wavelength of graphene‐based or hybrid graphene metasurfaces has been limited in the mid‐infrared and terahertz spectra. In this paper, by combining graphene with Au nanostructures, the authors demonstrate a near‐infrared tunable metasurface with decent modulation efficiency, weak dependence on graphene's carrier mobility, and small gate voltages, attributing to the unique interband transition of graphene. The experimental results agree well with numerical simulations. It is also shown that by properly designing the structural parameters of Au nanostructures, the hybrid graphene metasurface can be tunable in both near‐infrared and mid‐infrared regions.

Over the past decades, optical manipulation of magnetization by ultrafast laser pulses has attracted extensive interest. It not only shows intriguing fundamental science arising from the interactions between spins, electrons, phonons and photons, but also manifests the potential to process and store data at a speed that is three orders of magnitude faster than the current technologies. In this paper, we experimentally demonstrate all-optical helicity-dependent switching (AO-HDS) in hybrid metalferromagnet thin films, which consist of Co/Pt multilayers with perpendicular magnetic anisotropy and an Au film capping layer on the top. We have systematically studied the switching behaviors of the hybrid Co/Pt-Au material, with various laser repetition rates, scanning speeds and fluences. In comparison with bare Co/Pt multilayers, the hybrid metal-ferromagnet thin films show pronounced AO-HDS when the number of laser pulses per along the scanning direction gradually increases. In addition, the AO-HDS effect is very robust against laser fluences. We have further proposed a possible mechanism based on numerical simulations of the opto-magnetic coupling model, which indicate that the benefits of the Au layer in the AO-HDS process are twofold: serving as a good heat sink and substantially prolonging the effective magnetic field induced by the inverse Faraday effect. Our findings promise a new material system that exhibits stable AO-HDS phenomena, and hence could transform future magnetic storage devices, especially with the addition of plasmonic nanostructures made of noble metals.

Integrating solid‐state electrolyte (SSE) into Li‐metal anodes has demonstrated great promise to unleash the high energy density of rechargeable Li‐metal batteries. However, fabricating a highly cyclable SSE/Li‐metal anode remains a major challenge because the densification of the SSE is usually incompatible with the reactive Li metal. Here, a liquid‐metal‐derived hybrid solid electrolyte (HSE) is proposed, and a facile transfer technology to construct an artificial HSE on the Li metal is reported. By tuning the wettability of the transfer substrates, electron‐ and ion‐conductive liquid metal is sandwiched between electron‐insulating and ion‐conductive LiF and oxides to form the HSE. The transfer technology renders the HSE continuous, dense, and uniform. The HSE, having high ion transport, electron shut‐off, and mechanical strength, makes the composite anode deliver excellent cyclability for over 4000 h at 0.5 mA cm−2 and 1 mAh cm−2 in a symmetrical cell. When pairing with LiFePO4 and sulfur cathodes, the HSE‐coated Li metal dramatically enhances the performance of full cells. Therefore, this work demonstrates that tuning the interfacial wetting properties provides an alternate approach to build a robust solid electrolyte, which enables highly efficient Li‐metal anodes.

In this paper, we report all-optical manipulation of magnetization in ferromagnetic Co/Pt thin films enhanced by plasmonic resonances. By annealing a thin Au layer, we fabricate large-area Au nanoislands on top of the Co/Pt magnetic thin films, which show plasmonic resonances around the wavelength of 606 nm. Using a customized magneto-optical Kerr effect setup, we experimentally observe an 18.5% decrease in the minimum laser power required to manipulate the magnetization, comparing the on- and off-resonance conditions. The results are in very good agreement with numerical simulations. Our research findings demonstrate the possibility to achieve an all-optical magnetic recording with low energy consumption, low cost, and high areal density by integrating plasmonic nanostructures with magnetic media.

of external perturbation, controllable mode conversion with polarization change can be implemented. Recently, several methods have been proposed to achieve this goal. For example, waveguides with asymmetric cross-sections, [13][14][15][16][17][18] including L shape and double-stair shape, as well as asymmetric metallic cover layers, [19][20][21] can break the orthogonality of TE 0 and TM 0 mode and hence produce direct conversion between them. Such devices can function as polarization rotators, since the input and output modes always share the same mode order but with different polarization directions. Another method for polarization manipulation is based on mode evolution, where a mode hybridization region is used to gradually convert the input mode into the orthogonal polarization with the same or higher order. [11,22] However, this strategy requires a large length of the mode hybridization region up to hundreds of micrometers because it should satisfy the adiabatic transition condition.Metasurfaces, which are made up of an array of artificial subwavelength structures to locally manipulate the amplitude, phase, and polarization of light, represent one frontier in photonics research. [23][24][25][26][27][28][29][30][31][32] Based on elaborately designed metasurfaces, novel applications such as holographic image display, [33][34][35][36][37][38][39][40][41] imaging with meta-lenses, [42][43][44][45][46][47] orbital angular momentum (OAM) beam generation, [48][49][50][51][52][53] and polarization manipulation [54][55][56][57][58][59] have been demonstrated. However, most of these metasurfaces operate in free space, and the entire systems still consist of bulky optical components including light sources, mirrors, polarizers, etc. To further reduce the overall size and complexity, researchers have recently investigated the hybrid platform by integrating metasurfaces with photonic waveguides that preserve the merits of each system. Applications like mode converters, polarization rotators, second-harmonic generation, on-chip wavefront shaping and OAM lasers have been reported. [60][61][62][63][64][65][66][67] With the assistance of metasurfaces, the wavevector of the guided mode can be modified and the mode coupling coefficient can be optimized, ensuring the efficient conversion from the fundamental mode to higher-order mode. On the other hand, 2D phase shaping of the input planar waveguide mode was realized by deliberately controlling the local phase or refractive index with metasurfaces. [66,68,69] However, to the best of our knowledge, a universal and straightforward method for arbitrarily converting TM modes to TE modes or wavefront shaping for the cross-polarized waves is still lacking.In this paper, we propose a new design strategy for mode converters and polarization rotators utilizing on-chip C-shaped In this work, mode conversion and wavefront shaping by integrating a metallic metasurface on top of a planar waveguide are proposed and demonstrated. The metasurface consists of C-shaped nanoantennas. By controll...

Polaritons are quasiparticles originating from strong interactions between photons and elementary excitations that could enable high tunability, tight electromagnetic field confinement, and large density of photonic states, making it possible to achieve novel and otherwise inaccessible functionalities. For these reasons, polaritons spawn great interest in the fields of physics, materials science, and optics for both fundamental studies as well as potential applications (e.g., modulators, photodetectors, photoluminescence, etc.). In recent years, the explosive growth of research in graphene and other 2D van der Waals materials is witnessed because they provide a new platform that substantially complements conventional metals, dielectrics, and semiconductors to investigate different polariton modes. This review highlights the works published in recent years on the topic of polariton photonics based on structured metals, graphene, and transition‐metal dichalcogenides (TMDs). The exotic optical properties of the polaritons in metallic structures and 2D van der Waals materials offer bright prospects for the development of high‐performance photonic and optoelectronic devices.

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