An ultrawideband perfect absorber (UPA) is designed via a four-layer dielectric/refractory metal structure, which can produce near-unity absorption in the midinfrared region. The maximal absorption is up to 99.6%. Moreover, the absorber can maintain excellent absorption in a wide angle range, which indicates the angle-insensitive absorption and holds potential applications in complex electromagnetic situations. The ultrawideband spectral absorption mainly results from the intrinsic broadband plasmonic resonances by the refractory metals and the combination of the different plasmonic resonances by the resonators, and the cavity resonances by the layered nanostructures. Furthermore, due to the high melting point of titanium and chromium materials, the UPA is with highly thermal stability. The proposed absorber platform is therefore with both advantageous on the absorption properties and material features, which could pave ways for a wide application prospect in solar harvesting, infrared detection, and others.
Spectral coloring glass and its application on the surface-enhanced Raman scattering are demonstrated experimentally via a simple and moderate heat-treating of the top ultrathin gold film to create discrete nanoparticles, which can produce localized surface plasmon resonances and strong plasmonic near-field coupling effects. Ultrathin metal films with a wide range of thicknesses are investigated by different heat-treatment processes. The annealed metal films have been demonstrated with a series of spectral coloring responses. Moreover, the microscopy images of the metal film structures confirm the formation of distinct geometry features in these operation procedures. Densely packed nanoparticles are observed for the ultrathin metal film with the single-digit level of thickness. With increasing the film thickness over 10 nm, metallic clusters and porous morphologies can be obtained. Importantly, the metallic resonators can provide enhanced Raman scattering with the detection limit down to 10 − 7 molL − 1 of Rhodamine 6G molecules due to the excitation of plasmon resonances and strong near-field coupling effects. These features hold great potential for large-scale and low-cost production of colored glass and Raman substrate.
We present a theoretical investigation of the transmission properties of light through a metallic film perforated with different arrays of compound triangular holes. The extraordinary optical transmission (EOT) in the optical region is obtained by employing the finite-difference time-domain method. The excitation of localized surface plasmon resonances (LSPRs) at the top corners and surface plasmon polaritons (SPPs) on the metal surface, plasmon coupling effects between adjacent apertures, and the waveguide modes for delivering light mainly contribute to the EOT in such structures. The optical characteristics can be effectively tailored by changing the arrangement of triangular holes and the structural parameters. This study may be helpful for plasmonic nanostrucutres based on EOT, and has potential applications in optoelectronic devices.
We propose a thin metallic film perforated with a hexagonal periodic array of cubic holes and calculate its optical properties through the three-dimensional finite-difference time-domain method. Perfect superbroadband optical transparency from visible to near-infrared is achieved with the transmittance up to 99% due to the excitation of surface plasmon polaritons on the nanopatterned metal surface, localized surface plasmons at the edges of the cubic holes, and their cooperative interaction. The perfect superbroadband optical transparency of the proposed structure mainly depends on the size of holes and the period of the cubic hole array, and the proposed structure with perfect superbroadband optical transparency can resist to the interference of surrounding dielectric environment, which would provide fascinating potential applications in absorbers, solar cells, and transparent electrodes.
A double-time model software correlator with 5ns time resolution was presented. This correlator includes 12 independent linear correlators. A simple algorithm used for counting the number of photon signals and computing the correlation function on line, was complied by using the graphical programming language Labview8.2. By using of a photomultiplier tube (PMT), a National Instruments Model PXI-5152 high-speed acquisition board, a National Instruments Model PXI-8105 control system, correlation functions can be worked out in real time over time scales of 5μs and processing in blocks down to time scales of ~10ms. Its performances were tested by using polystyrene spheres and silicon dioxide spheres diluted in water. These two kinds of nanoparticles are in different sizes. The correlation functions computed indicate that our correlator is feasible to compute the correlation functions in photon correlation spectroscopy (PCS).