Kuang-Yu Yang

We combine theory and experiment to demonstrate that a carefully designed gradient meta-surface supports high-efficiency anomalous reflections for near-infrared light following the generalized Snell's law, and the reflected wave becomes a bounded surface wave as the incident angle exceeds a critical value. Compared to previously fabricated gradient meta-surfaces in infrared regime, our samples work in a shorter wavelength regime with a broad bandwidth (750-900 nm), exhibit a much higher conversion efficiency (∼80%) to the anomalous reflection mode at normal incidence, and keep light polarization unchanged after the anomalous reflection. Finite-difference-time-domain (FDTD) simulations are in excellent agreement with experiments. Our findings may lead to many interesting applications, such as antireflection coating, polarization and spectral beam splitters, high-efficiency light absorbers, and surface plasmon couplers.

Split-ring resonators (SRRs) have been the subject of investigation as plasmonic sensors that operate by sensing plasmon resonance shift δλ when exposed to a medium with a refractive index change δn. However, conventional planar SRRs have their plasmon fields spread into the substrates, reducing accessible sensing volume and its sensing performance. Such a limitation can be eradicated with vertical SRRs in which the plasmon fields localized in SRR gaps are lifted off from the substrate, allowing for greatly enhanced sensitivity. Here, we demonstrate the highest sensitivity among reported SRR-based sensors in optical frequencies.

We demonstrate a self-assembly strategy for fabricating three dimensional (3D) metamaterials. This strategy represents the desired 3D curving prongs of the split ring resonators (SRRs) erected by metal stress force with appropriate thin film parameters. Transmittance spectra and field patterns corresponding to each resonance modes are calculated by finite element method (FEM). The eigen-modes of the SRRs can be excited by normal illumination with polarization state parallel to the erected SRRs, which are unlike for the cases of planar SRRs. This method opens a promising fabrication process for the application of tailored 3D SRRs.

The preparation and properties of plasmonic gold nanostars (Au NSs) modified with a biopolymer chitosan are reported. The colloidal stability of Au NSs at the physiological pH of 7.5 and their performance in the photothermolysis of cancer cells in vitro were compared with those of gold nanorods (Au NRs). The optical characteristics of chitosan-modified Au NSs dispersed in a medium with pH = 7.5 had higher stability than those of chitosan-capped NRs because of the slower aggregation of NSs. At pH = 7.5, the chitosan-modified Au NRs formed aggregates with highly nonuniform sizes. On the other hand, Au NSs formed small chain-like clusters, in which individual NSs were connected to one another, preferably via association of branches with central cores. It is possible that the difference in areal charge density at these parts of NSs is responsible for their preferred association. Flow cytometry analysis showed the relatively nonequivalent distribution of the chitosan-capped Au NRs across the cell line compared with that of Au NSs because of the fast and nonuniform aggregation of NRs. An in-vitro photothermolysis experiment on J5 cancer cells showed that energy fluences of 23 and 33 mJ/cm2 are necessary to cause complete death of J5 cells incubated with 4 μg/mL chitosan-capped Au NSs and NRs, respectively. When chitosan was used as a surface-capping agent, the Au NSs exhibited higher colloidal stability at the physiological pH than the NRs and lower energy fluence necessary for cell photothermolysis because of more uniform cellular uptake.

Holograms, the optical devices to reconstruct pre-designed images, have been advanced dramatically with the development of today’s nanotechnology [1-2]. However, applications of hologram are still limited by the constituent materials, and their working range is rather narrow. In the past decade, plasmonic metamaterials [3] have attracted many attentions, which exhibit strong variations in their reflectance and/or transmittance spectra. Moreover, metasurfaces show the abilities to exhibit extraordinary light-manipulation abilities [4-5]. In this paper, we reported the high-efficiency and broadband meta-hologram consisted of plasmonic metamaterials, which functions for both coherent and incoherent light sources within a broad spectral range under a wide range of incidence angles [6].