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.

Ionizing particles impacting the photosensing cell of an image sensor induces a current, and event rate statistics can be used to measure the extent of radiation contamination. This paper presents a simple algorithm for detecting ionizing radiation by using the image module of a smartphone. Ionizing radiation exposure experiments revealed that the proposed device has high sensitivity at radiation exceeding 10 μSv/h. Although the CMOS image sensor of a smartphone cannot be used to measure background radiation, it enables the convenient detection of ionizing radiation exceeding 10 μSv/h.

Simplified algorithm of ionizing radiation detecting based on image sensor

PROBLEM TO BE SOLVED: To provide a measurement system for gamma ray dose rate that increases convenience in useSOLUTION: A light shield device 100 filtrates light passing through the light shield device 100 by cutting off visible light An electronic device 200 includes a detection module 201, an image analysis module 203, and a display module 204 The detection module 201 detects gamma rays and generates a current signal The image analysis module 203 receives a current signal and analyzes the current signal, and then generates an analysis result including the total of gamma ray dose rates and a gamma ray energy spectrum A display module 204 displays the analysis result

Measurement system for gamma ray dose rate

Metasurfaces composed of artificial structures have attracted a huge number of interests due to their ability on controlling the electromagnetic phase and amplitude at subwavelength scale. Beside those promising characteristics, people now intend to discover the field of meta-devices, where we can attain optical functionalities through changing the features of metasurfaces in demand. In this talk, several metasurface based components for photonic applications will be performed and discussed, including versatile polarization control, pixel-scale metalens, and achromatic meta-devices.

Meta-Device for Photonics in Demand

Simulations and near-field measurements indicated that collective surface plasmons of silver nanoparticle clusters resulted in the super-resolution property of the AgOx-type super-resolution near-field structure. Randomly distributed metallic nanoparticle clusters transferred evanescent signals from subwavelength objects to propagating waves like a near-field probe and circumvented the diffraction limit.

Enhanced resolution with metallic nanoparticle clusters

We use a 60 × 60 dielectric achromatic metalens array to capture multidimensional optical information including both image and depth. The scene can be reconstructed slice by slice from a series of rendered full-color images. © 2019 The Author(s)

Din Ping Tsai

Papers

Simplified algorithm of ionizing radiation detecting based on image sensor

Measurement system for gamma ray dose rate

Meta-Device for Photonics in Demand

Enhanced resolution with metallic nanoparticle clusters

Metalens for light field imaging