We perform a comprehensive analysis of multi-band absorption by exciting magnetic polaritons in the infrared region. According to the independent properties of the magnetic polaritons, we propose a parallel inductance and capacitance(PLC) circuit model to explain and predict the multi-band resonant absorption peaks, which is fully validated by using the multi-sized structure with identical dielectric spacing layer and the multilayer structure with the same strip width. More importantly, we present the application of the PLC circuit model to preliminarily design a radiative cooling structure realized by merging several close peaks together. This omnidirectional and polarization insensitive structure is a good candidate for radiative cooling application.

Near-field radiative heat transfer (RHT) between two bodies can significantly exceed the far-field limit set by Planck's law due to the evanescent wave tunneling, which typically can only occur when the two bodies are separated at subwavelength distances. We show that the RHT between two SiC nanoparticles with separation distances much larger than the thermal wavelength can still exceed the far-field limit when the particles are located within a subwavelength distance away from a SiC substrate. In this configuration, the localized surface phonon polariton (SPhP) of the particles couples to the propagating SPhP of the substrate which then provides a new channel for the near-field energy transport and enhances the RHT by orders of magnitude at large distances. The enhancement is also demonstrated to appear in a chain of closely spaced SiC nanoparticles located in the near field of a SiC substrate. The findings provide a way for the long-distance transport of near-field energy.

The many-body radiative heat transfer theory [P. Ben-Abdallah, S.-A. Biehs, and K. Joulain, Phys. Rev. Lett. 107, 114301 (2011)] considered only the contribution from the electric dipole moment. For metal particles, however, the magnetic dipole moment due to eddy current plays an important role, which can further couple with the electric dipole moment to introduce crossed terms. In this paper, we develop the coupled electric and magnetic dipole (CEMD) approach for the radiative heat transfer in a collection of objects in mutual interaction. Due to the coupled electric and magnetic interactions, four terms, namely the electric-electric, the electric-magnetic, the magnetic-electric, and the magnetic-magnetic terms, contribute to the radiative heat flux and the local energy density. The CEMD is applied to study the radiative heat transfer between various dimers of nanoparticles. It is found that each of the four terms can dominate the radiative heat transfer depending on the position and composition of particles. Moreover, near-field many-body interactions are studied by CEMD considering both dielectric and metallic nanoparticles. The near-field radiative heat flux and local energy density can be greatly increased when the particles are in coupled resonances. Surface plasmon polariton and surface phonon polariton can be coupled to enhance the radiative heat flux.

The optical properties of sodium chloride (NaCI) solution were experimentally determined by double optical pathlength transmission method in the spectral range from 300 to 2500 nm at the NaCl concentration range from 0 to 360 g/L. The results show that the refractive index of NaCl solution increases with NaCl concentrations and correlates nonlinearly with the concentration of NaCl solution. The absorption index of NaCl solution increases with NaCl concentrations in the visible spectral range of 300-700 nm, but varies little in the near-infrared spectral range of 700-2500 nm at room temperature. For the sake of applications, the fitted formulae of the refractive index and absorption index of NaCl solution as a function of wavelength and NaCl concentration are presented.

An infrared dual-band perfect absorber based on asymmetric T-shaped plasmonic array is designed and numerically investigated. Two distinct absorption peaks are achieved by localized surface plasmon polariton (LSPP) mode over a wide incident angular range. Both the absorption peaks can be finely tuned independently by varying the geometry of the structure. In our proposed structure, the period of the T-shaped structures becomes less and the multiple LSPP peaks are suppressed, which result in the sideband of absorption peaks very low. This dual-band perfect absorber has potential applications such as in infrared imaging devices, thermal bolometers, and wavelength selective radiators.