Metamaterials are artificially fabricated materials that allow for the control of light and acoustic waves in a manner that is not possible in nature. This Review covers the recent developments in the study of so-called metasurfaces, which offer the possibility of controlling light with ultrathin, planar optical components. Conventional optical components such as lenses, waveplates and holograms rely on light propagation over distances much larger than the wavelength to shape wavefronts. In this way substantial changes of the amplitude, phase or polarization of light waves are gradually accumulated along the optical path. This Review focuses on recent developments on flat, ultrathin optical components dubbed 'metasurfaces' that produce abrupt changes over the scale of the free-space wavelength in the phase, amplitude and/or polarization of a light beam. Metasurfaces are generally created by assembling arrays of miniature, anisotropic light scatterers (that is, resonators such as optical antennas). The spacing between antennas and their dimensions are much smaller than the wavelength. As a result the metasurfaces, on account of Huygens principle, are able to mould optical wavefronts into arbitrary shapes with subwavelength resolution by introducing spatial variations in the optical response of the light scatterers. Such gradient metasurfaces go beyond the well-established technology of frequency selective surfaces made of periodic structures and are extending to new spectral regions the functionalities of conventional microwave and millimetre-wave transmit-arrays and reflect-arrays. Metasurfaces can also be created by using ultrathin films of materials with large optical losses. By using the controllable abrupt phase shifts associated with reflection or transmission of light waves at the interface between lossy materials, such metasurfaces operate like optically thin cavities that strongly modify the light spectrum. Technology opportunities in various spectral regions and their potential advantages in replacing existing optical components are discussed.

Flat Optics With Designer Metasurfaces

Recent years have seen a renewed interest in the harvesting and conversion of solar energy. Among various technologies, the direct conversion of solar to chemical energy using photocatalysts has received significant attention. Although heterogeneous photocatalysts are almost exclusively semiconductors, it has been demonstrated recently that plasmonic nanostructures of noble metals (mainly silver and gold) also show significant promise. Here we review recent progress in using plasmonic metallic nanostructures in the field of photocatalysis. We focus on plasmon-enhanced water splitting on composite photocatalysts containing semiconductor and plasmonic-metal building blocks, and recently reported plasmon-mediated photocatalytic reactions on plasmonic nanostructures of noble metals. We also discuss the areas where major advancements are needed to move the field of plasmon-mediated photocatalysis forward.

Plasmonic-metal nanostructures for efficient conversion of solar to chemical energy

Since its discovery, the asymmetric Fano resonance has been a characteristic feature of interacting quantum systems. The shape of this resonance is distinctively different from that of conventional symmetric resonance curves. Recently, the Fano resonance has been found in plasmonic nanoparticles, photonic crystals, and electromagnetic metamaterials. The steep dispersion of the Fano resonance profile promises applications in sensors, lasing, switching, and nonlinear and slow-light devices.

The Fano resonance in plasmonic nanostructures and metamaterials

We present an introduction to surface-enhanced Raman scattering (SERS) which reviews the basic experimental facts and the essential features of the mechanisms which have been proposed to account for the observations. We then review very recent fundamental developments which include: SERS from single particles and single molecules; SERS from fractal clusters and surfaces; and new insights into the chemical enhancement mechanism of SERS.

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Surface-enhanced Raman scattering

Plasmons in strongly coupled metallic nanostructures.

Silver nanorods have an excellent effect on the transmitted wave localizing, especially, the intensity of the transmitted wave is strong enough below the bottom of the nanorods. Based on this property, we offer a non-touched optical nanolithographic imaging method, and the structure of the mask is made by silver nanorods which are embedded in a silica block. We numerically prove the availability of the nanolithography in visible domain, and a high resolution of nanolithographic image can be built by a multi-exposures process.

None-touched Near-field Optical Nanolithography

Alpha-Fe2O3 (α-Fe2O3) is cheap and abundant and has potential to be a highly efficient photocatalyst for water splitting. According to the report, there are a huge amount of disposable heating pads being created every year, and the pads are used one time then thrown away. We found that the main product of used heating pads is α-Fe2O3. Here, we collect and purify the α-Fe2O3 powder in the used heating pads using low power consumption processes. It is shown that the recycled heating pads can be used as a cost-effective photocatalyst for H2 energy and for decomposition of organic pollutants as well. Additionally, the plasmonic enhanced photocatalysis reaction of α-Fe2O3 is also investigated. It is found that H2 evolution rate can be enhanced 15% using α-Fe2O3 nanoparticles coated with a thin Au layer. The degradation of methylene blue can also enhance 12% compared to photocatalyst α-Fe2O3 nanoparticles coated without Au layer.

Visible light active photocatalyst from recycled disposable heating pads

In this paper we investigate the change of surface plasma (SP) resonance of a left-handed material (LHM) nano-slab. 
The intrinsic parameters of the LHM slab are suitable chose so that it has both negative permittivity and permeability in a
frequency range of visible light. We calculate the attenuated total reflection (ATR) spectra of the LHM slab by use of 
the transfer matrix method. The spectra of different cases with various slab thickness and surrounding dielectrics of the 
LHM slab have been studied. The variations of SP resonance wavenumber and the corresponding resonance strength are 
discussed from the results of calculated ATR spectra.

Behavior of surface plasmon resonance at a left-handed material nano slab

Dataset supports: Savinov, V. et al (2019). Optical Anapoles. Communications Physics.PLY files (Polygon File Format) of the logarithm of the value of ellipticity for the negative and positive ellipticities of the light emitted by the accelerated electric dipole. PLY files contain the surface that gives the log-value of the ellipticity as the function of angle. Fig. 4b in the paper.

Dataset for: Optical Anapoles

We show that Landau damping presents the most practically-relevant limit to the achievable plasmonic enhancement inside the narrow gaps of plasmonic dimers and other similarly-shaped plasmonic nanoantennas.

Din Ping Tsai

Papers

None-touched Near-field Optical Nanolithography

Visible light active photocatalyst from recycled disposable heating pads

Behavior of surface plasmon resonance at a left-handed material nano slab

Dataset for: Optical Anapoles

Impact of Landau damping on field enhancement in plasmonic dimers