The simultaneous realization of high Q-factor resonances and strong near-field enhancements around and inside of dielectric nanostructures is important for many applications in nanophotonics. However, the incident fields are often confined within dielectric nanoparticles, which results in poor optical interactions with external environment. Near-field enhancements can be extended outside of dielectric nanostructures with proper design, but the Q-factor is often reduced caused by additional radiation losses. This paper shows that the obstacles to achieve high Q-factor, that is, the radiative losses can be effectively suppressed by using dielectric nanodisk arrays, where the Q-factor is about one order larger than that of the single disks associated with the nonradiating anapole modes and the collective oscillations of the arrays. When the resonance energies of the electric dipole mode and the subradiant mode are degenerate with each other, the destructive interference produces an effect analogous to electromagnetically induced transparency. Furthermore, the Q-factor can be extremely enlarged with dielectric split nanodisk arrays, where the present of the split gap does not induce additional losses. Instead, the coupling between the two interfering modes is modified by adjusting the gap width, which makes it possible to achieve high Q-factor and strong near-field enhancements around and inside of the split disks simultaneously. It is shown that the Q-factor is approaching to 10 when the gap width is about 110 nm, and the near-field enhancements around and inside of the split disks are about two orders stronger than that of the single disk.

The nonradiating nature of anapole modes owing to the compositions of electric and toroidal dipole moments makes them distinct from conversional radiative resonances, and they have been suggested for the design of nanophotonic devices such as nanolasers based on light−matter interactions tailor by nanodisks. Therefore, the investigation of resonance coupling between molecular excitons and anapole modes is not only of fundamental interest, but is also promising for practical applications. To this end, a heterostructure composed of a silicon nanodisk and a uniform molecular J-aggregate ring is used to achieve the resonance coupling between the exciton transition and the anapole mode. In contrast with that of the conversional resonances, the resonance coupling is evidenced by a scattering peak around the exciton transition frequency, and the anapole mode splits into a pair of eigenmodes characterized as pronounced scattering dips, which are termed as the formation of two hybrid anapole modes caused by the coherent energy exchange in the heterostructure, and it has been verified by the multipole decompositions and the near-field distributions. An anticrossing behavior with a mode splitting of 161 meV is observed on the energy diagram, indicating that the strong coupling regime is achieved. Furthermore, due to the unique near-field distribution associated with the anapole mode, there is a much larger upper limit value for the width of the J-aggregate ring to enhance the resonance coupling, and the molecules located around the apexes of the disk perpendicular to the incident polarization play the dominate role for the resonance coupling.

Solar steam generation provides a renewable and environmentally friendly approach to solve the water shortage issue. The pursuit of efficient, stable, and cheap photothermal agents is thus of great significance. In this work, Cu nanoparticles (NPs) fabricated simply by a substitution reaction, exhibit a near-unity (∼97.7%) light absorption, covering a broad incident angle and wavelength range (200–1300 nm). Thereby, a high photothermal conversion efficiency of 93% is achieved. The excellent photothermal performance offers a unique opportunity for the development of solar steam generation. By coating the Cu NPs on a cellulose membrane, a solar steam generation efficiency up to 73% is acquired at a low irradiation power density of 2 kW m−2 (1 kW m−2 = 1 sun). Moreover, the Cu NPs are recyclable with the high stability being resistant to heat, photoirradiation and corrosion of brine.

Fano resonances in plasmonic nanostructures suppress radiative losses effectively, but non-radiative Ohmic losses limit the performance of many important applications. In addition, it is hard to generate strong Fano resonances in a single plasmonic homogeneous nanoparticle with high structural symmetry. Dielectric nanostructures offer a potential solution to the above issues. There are various subradiant hybrid modes in a single dielectric nanoparticle, making it possible to generate Fano resonances. This study shows that due to the excitation of the subradiant hybrid EH 12δ mode, a strong Fano resonance is generated in a single silicon nanodisk. Higher order subradiant hybrid modes (EH 13δ and EH 14δ ) are excited by manipulating the disk radius, and multiple Fano resonances arise in spectra. These optical responses are not dependent on retardation effect, and strong Fano resonances are generated even for a very thin disk. One can get similar results in a single dielectric triangle, square, or rectangle nanoplate. The simple geometry and high structural symmetry make these dielectric nanoparticles promising for practical implementations in biosensing and optoelectronics.

Spectral-based methods are often used for label-free biosensing. However, practical implementations with plasmonic nanostructures suffer from a broad line width caused by strong radiative and nonradiative losses, and the sensing performance characterized by figure of merit is poor for these spectral-based methods. This study provides a polarization state-based method using plasmonic nanostructures to improve the sensing performance. Instead of the intensity spectrum, the polarization state of the transmitted field is monitored to analyze variations of the surrounding medium. The polarization state of incidence is strongly modified due to the excitation of surface plasmons, and the ellipticity of the transmitted field changes dramatically around plasmon resonances. Sharp resonances with line widths down to sub-nanometer are achieved by plotting the spectra of the reciprocal of ellipticity. Therefore, the sensing performance can be significantly improved, and a theoretical value of the figure of merit exceeding 1700 is achieved by using the polarization state-based sensing approach.