Surface plasmons are coherent and collective electron oscillations confined at the dielectric–metal interface. Benefitting from the inherent subwavelength nature of spatial profile, surface plasmons can greatly accumulate the optical field and energy on the nanoscale and dramatically enhance various light–matter interactions. The properties of surface plasmons are strongly related to materials and structures, so that metals, semiconductors and two-dimensional materials with various morphologies and structures can have alternating plasmonic wavelengths ranging from ultraviolet, visible, near infrared to far infrared. Because the electric field can be enhanced by orders of magnitude within plasmonic structures, various light–matter interaction processes including fluorescence, Raman scattering, heat generation, photoacoustic effects, photocatalysis, nonlinear optical conversion, and solar energy conversion, can be significantly enhanced and these have been confirmed by both theoretical, computational and experimental studies. In this review, we present a concise introduction and discussion of various plasmon-enhanced light–matter interaction processes. We discuss the physical and chemical principles, influencing factors, computational and theoretical methods, and practical applications of these plasmon-enhanced processes and phenomena, with a hope to deliver guidelines for constructing future high-performance plasmonic devices and technologies.

On-site nano-kirigami enabled continuous shape transformation of gold nanofilm for 3D nanofabrication and giant optical chirality.

Advanced kirigami/origami provides an automated technique for modulating the mechanical, electrical, magnetic and optical properties of existing materials, with remarkable flexibility, diversity, functionality, generality, and reconfigurability. In this paper, we review the latest progress in kirigami/origami on the microscale/nanoscale as a new platform for advanced 3D microfabrication/nanofabrication. Various stimuli of kirigami/origami, including capillary forces, residual stress, mechanical stress, responsive forces, and focussed-ion-beam irradiation-induced stress, are introduced in the microscale/nanoscale region. These stimuli enable direct 2D-to-3D transformations through folding, bending, and twisting of microstructures/nanostructures, with which the occupied spatial volume can vary by several orders of magnitude compared to the 2D precursors. As an instant and direct method, ion-beam irradiation-based tree-type and close-loop nano-kirigami is highlighted in particular. The progress in microscale/nanoscale kirigami/origami for reshaping the emerging 2D materials, as well as the potential for biological, optical and reconfigurable applications, is briefly discussed. With the unprecedented physical characteristics and applicable functionalities generated by kirigami/origami, a wide range of applications in the fields of optics, physics, biology, chemistry and engineering can be envisioned.

Raman spectroscopy is a powerful analytical tool that probes vibrational fingerprints of molecules and enables high-content analysis of composite systems of physical, chemical, and biological interests by virtue of its inherent specificity. As an optical technique, Raman spectroscopy is noninvasive and versatile for studying solid, liquid, and gas samples and has been used for various applications, such as chemical detection, disease diagnosis, and environmental monitoring.¹ However, Raman spectroscopy suffers from low sensitivity, as spontaneous Raman scattering is intrinsically very weak. Only about 1 in $\sim {10}^7\text{photons}$ that interact with molecules undergoes Raman scattering.² The low sensitivity of Raman spectroscopy severely limits its practical applications, which range from trace-amount molecular detection to real-time bioimaging.

We report a two-dimensional heterogeneous Haldane model composed of alternately stacking modified Haldane lattices with opposite next-nearest-neighbor hoppings, and predict the emergence of robust one-way bulk states by an ab initio theoretical calculation. These unique bulk states transport unidirectionally and are robust against backscattering from impurities in the strip bulk. By analogy with the heterogeneous Haldane model, we further confirm by numerical simulations and experimental measurements the existence of robust one-way bulk states in a two-dimensional microwave gyromagnetic photonic crystal, and demonstrate their robust one-way property over a long-distance even in the presence of metallic obstacles. Our study provides the strong support for the generalization and application of band theories to fermionic and bosonic systems, and paves a way for the implementation of high-throughput robust energy transmission materials and devices.

We design and present a switchable slow light rainbow trapping (SLRT) state in a strongly coupling topological photonic system made from a magneto-optical photonic crystal waveguide channel. The waveguide channel supports slow light states with extremely small group velocity ($v_g=2.1\times {10}^{-6}c$), low group-velocity dispersion, and a broadband operation bandwidth (3.60–4.48 GHz, near 22% of bandwidth). These slow light states originate from the strong coupling between two counter propagating topological photonic states. Under a gradient magnetic field, different frequency components of a wave packet are separated and stored at different positions for a long temporal duration with high spatial precision (without crosstalk and overlap between the electric fields of different frequencies) to form SLRT. Besides, these SLRT states can be easily switched among the forbidden state, trapped state, and releasing state by tuning the external magnetic field. The results suggest that the topological photonic state can offer a precise route of spatial-temporal-spectral control upon a light signal and find applications for optical buffers, broadband slow light systems, optical filters, wavelength-division multiplexing, and other optical communication devices.