Laser-Induced Periodic Ag Surface Structure with Au Nanorods Plasmonic Nanocavity Metasurface for Strong Enhancement of Adenosine Nucleotide Label-Free Photoluminescence Imaging.
ABSTRACT: The label-free detection of biomolecules by means of fluorescence spectroscopy and imaging is topical. The developed surface-enhanced fluorescence technique has been applied to achieve progress in the label-free detection of biomolecules including deoxyribonucleic acid (DNA) bases. In this study, the effect of a strong enhancement of photoluminescence of 5'-deoxyadenosine-monophosphate (dAMP) by the plasmonic nanocavity metasurface composed of the silver femtosecond laser-induced periodic surface structure (LIPSS) and gold nanorods or nanospheres has been realized at room temperature. The highest value of 1220 for dAMP on the Ag-LIPSS/Au nanorod metasurface has been explained to be a result of the synergetic effect of the generation of hot spots near the sharp edges of LIPSS and Au nanorod tips together with the excitation of collective gap mode of the cavity due to strong near-field plasmonic coupling. A stronger plasmonic enhancement of the phosphorescence compared to the fluorescence is achieved due to a greater overlap of the phosphorescence spectrum with the surface plasmon spectral region. The photoluminescence imaging of dAMP on the metasurfaces shows a high intensity in the blue range. The comparison of Ag-LIPSS/Au nanorod and Ag-LIPSS/Au-nanosphere metasurfaces shows a considerably higher enhancement for the metasurface containing Au nanorods. Thus, the hybrid cavity metasurfaces containing metal LIPSS and nonspherical metal nanoparticles with sharp edges are promising for high-sensitive label-free detection and imaging of biomolecules at room temperature.
Project description:Quasi two-dimensional metasurfaces composed of subwavelength nanoresonator arrays can dramatically alter the properties of light in an ultra-thin planar geometry, enabling new optical functions such as anomalous reflection and refraction, polarization filtering, and wavefront modulation. However, previous metasurface-based nanostructures suffer from low efficiency, narrow bandwidth and/or limited field-of-view due to their operation near the plasmonic resonance. Here we demonstrate plasmonic metasurface-based nanostructures for high-efficiency, angle-insensitive polarization transformation over a broad octave-spanning bandwidth. The structures are realized by optimizing the anisotropic response of an array of strongly coupled nanorod resonators to tailor the interference of light at the subwavelength scale. Nanofabricated reflective half-wave and quarter-wave plates designed using this approach have measured polarization conversion ratios and reflection magnitudes greater than 92% over a broad wavelength range from 640 to 1290 nm and a wide field-of-view up to ± 40°. This work outlines a versatile strategy to create metasurface-based photonics with diverse optical functionalities.
Project description:Metasurfaces are two-dimensional nanoantenna arrays that can control the propagation of light at will. In particular, plasmonic metasurfaces feature ultrathin thicknesses, ease of fabrication, field confinement beyond the diffraction limit, superior nonlinear properties, and ultrafast performances. However, the technological relevance of plasmonic metasurfaces operating in the transmission mode at optical frequencies is questionable due to their limited efficiency. The state-of-the-art efficiency of geometric plasmonic metasurfaces at visible and near-infrared frequencies, for example, is ≤10%. Here, we report a multipole-interference-based transmission-type geometric plasmonic metasurface with a polarization conversion efficiency that reaches 42.3% at 744 nm, over 400% increase over the state of the art. The efficiency is augmented by breaking the scattering symmetry due to simultaneously approaching the generalized Kerker condition for two orthogonal polarizations. In addition, the design of the metasurface proposed in this study introduces an air gap between the antennas and the surrounding media that confines the field within the gap, which mitigates the crosstalk between meta-atoms and minimizes metallic absorption. The proposed metasurface is broadband, versatile, easy to fabricate, and highly tolerant to fabrication errors. We highlight the technological relevance of our plasmonic metasurface by demonstrating a transmission-type beam deflector and hologram with record efficiencies.
Project description:Metasurfaces are ultrathin, two-dimensional arrays of subwavelength resonators that have been demonstrated to control the flow of light in ways that are otherwise unattainable with natural materials. These arrays are typically composed of metallic Ag or Au nanostructures shaped like split rings, nanowire pairs or nanorods (commonly referred to as meta-atoms) that are arranged to produce a collective optical response spanning an impressive range of properties, from the perfect absorption of incident light to superresolution imaging. However, metasurfaces pose major challenges in their fabrication over large areas, which can be prohibitively expensive and time consuming using conventional nanolithography techniques. Here we show that differently shaped colloidal nanocrystals can be organized into metasurface architectures using robust, scalable assembly methods. These metasurfaces exhibit extreme in-plane electromagnetic coupling that is strongly dependent on nanocrystal size, shape and spacing. Colloidal metasurfaces that display near-ideal electromagnetic absorbance can be tuned from the visible into the mid-infrared wavelengths.
Project description:Given the development of nano/microscale patterning techniques, efforts are being made to use them for fabricating metasurfaces. In particular, by using abrupt phase discontinuities, it is possible to generate holographic images from two-dimensional nanoscale-patterned metasurfaces. However, the fabrication of metasurface holograms is hindered by the high costs and long fabrication time involved, because the process requires expensive equipment such as that for electron-beam lithography. Therefore, it is difficult to realize metasurface holograms in a fast and repetitive manner. In this study, we propose a method for fabricating metasurface holograms based on the nanotransfer printing of the desired nanoscale patterns, which is assisted by Au nanoclusters, while controlling the bonding energy based on the shape of the deposited Au layer. Robust covalent bonds are formed between the Si of the adhesive used and the O of the SiO2 layer in order to transfer the deposited Au onto the transparent substrate quickly. It was found that the fabricated metasurface hologram coincides with the one designed by computer-generated holography. The proposed method should lead to a significant breakthrough in the fabrication of holograms based on different types of metasurfaces at a low cost in a fast, repetitive manner with various metals.
Project description:A graphene-based plasmonic metasurface which can independently control different polarized electromagnetic waves with reasonably small losses in terahertz regime is proposed and demonstrated in this paper. This metasurface is composed of graphene based elements. Owing to anisotropic plasmonic resonance of the graphene-based elements, the reflected phases and magnitudes of orthogonally polarized waves can be independently controlled by varying dimensions of the element. Four types of graphene-based plasmonic metasurfaces with different reflected phases distributions are synthesized and simulated, exhibiting diverse functions such as polarized beam splitting, beam deflection, and linear-to-circular polarization conversion. The simulation results demonstrate excellent performances as theoretical expectation. The proposed graphene-based plasmonic metasurface can be applied to realize extremely light-weight, ultra-compact, and high-performances electromagnetic structures for diverse terahertz applications.
Project description:Metasurfaces enable manipulation of light propagation at an unprecedented level, benefitting from a number of merits unavailable to conventional optical elements, such as ultracompactness, precise phase and polarization control at deep subwavelength scale, and multifunctionalities. Recent progress in this field has witnessed a plethora of functional metasurfaces, ranging from lenses and vortex beam generation to holography. However, research endeavors have been mainly devoted to static devices, exploiting only a glimpse of opportunities that metasurfaces can offer. We demonstrate a dynamic metasurface platform, which allows independent manipulation of addressable subwavelength pixels at visible frequencies through controlled chemical reactions. In particular, we create dynamic metasurface holograms for advanced optical information processing and encryption. Plasmonic nanorods tailored to exhibit hierarchical reaction kinetics upon hydrogenation/dehydrogenation constitute addressable pixels in multiplexed metasurfaces. The helicity of light, hydrogen, oxygen, and reaction duration serve as multiple keys to encrypt the metasurfaces. One single metasurface can be deciphered into manifold messages with customized keys, featuring a compact data storage scheme as well as a high level of information security. Our work suggests a novel route to protect and transmit classified data, where highly restricted access of information is imposed.
Project description:Metasurfaces, as a two-dimensional (2D) version of metamaterials, have drawn considerable attention for their revolutionary capability in manipulating the amplitude, phase, and polarization of light. As one of the most important types of metasurfaces, geometric metasurfaces provide a versatile platform for controlling optical phase distributions due to the geometric nature of the generated phase profile. However, it remains a great challenge to design geometric metasurfaces for realizing spin-switchable functionalities because the generated phase profile with the converted spin is reversed once the handedness of the incident beam is switched. Here, we propose and experimentally demonstrate chiral geometric metasurfaces based on intrinsically chiral plasmonic stepped nanoapertures with a simultaneously high circular dichroism in transmission (CDT) and large cross-polarization ratio (CPR) in transmitted light to exhibit spin-controlled wavefront shaping capabilities. The chiral geometric metasurfaces are constructed by merging two independently designed subarrays of the two enantiomers for the stepped nanoaperture. Under a certain incident handedness, the transmission from one subarray is allowed, while the transmission from the other subarray is strongly prohibited. The merged metasurface then only exhibits the transmitted signal with the phase profile of one subarray, which can be switched by changing the incident handedness. Based on the chiral geometric metasurface, both chiral metasurface holograms and the spin-dependent generation of hybrid-order Poincaré sphere beams are experimentally realized. Our approach promises further applications in spin-controlled metasurface devices for complex beam conversion, image processing, optical trapping, and optical communications.
Project description:Metasurfaces are engineered interfaces that contain a thin layer of plasmonic or dielectric nanostructures capable of manipulating light in a desirable manner. Advances in metasurfaces have led to various practical applications ranging from lensing to holography. Metasurface holograms that can be switched by the polarization state of incident light have been demonstrated for achieving polarization multiplexed functionalities. However, practical application of these devices has been limited by their capability for achieving high efficiency and high image quality. Here we experimentally demonstrate a helicity multiplexed metasurface hologram with high efficiency and good image fidelity over a broad range of frequencies. The metasurface hologram features the combination of two sets of hologram patterns operating with opposite incident helicities. Two symmetrically distributed off-axis images are interchangeable by controlling the helicity of the input light. The demonstrated helicity multiplexed metasurface hologram with its high performance opens avenues for future applications with functionality switchable optical devices.
Project description:Metasurfaces offer exciting opportunities that enable precise control of light propagation, optical intensity, phase and polarization. Plasmonic metasurface based quarter-wave plates have been recently studied to realize the conversion between linear polarization and circular polarization. However, it is still quite challenging to directly measure the birefringent phase retardation introduced by metasurface wave plates with a reliable technique. Here, we report a high-performance broadband metasurface quarter-wave plate made of anisotropic T-shaped plasmonic antennas in near-infrared wavelength range, where the achromatic nearly 90° transmitted phase retardation through the metasurface is precisely characterized with an optical vortex based interferometric approach. Based on the measured transmission amplitude and phase of two orthogonal linear polarization components, nearly unit degree of linear polarization is extracted from the Stokes parameters, indicating excellent broadband polarization conversion between linearly and circularly polarized light through the metasurface. Our results will be an important step forward in the advancement of integrated metasurface devices for polarization conversion and beam manipulation, structured light control, as well as new spectroscopic and interferometric techniques for metasurface characterization.
Project description:Metamaterials are artificial materials made of subwavelength elementary cells that give rise to unexpected wave properties that do not exist naturally. However, these properties are generally achieved due to 3D patterning, which is hardly feasible at short wavelengths in the visible and near-infrared regions targeted by most photonic applications. To overcome this limitation, metasurfaces, which are the 2D counterparts of metamaterials, have emerged as promising platforms that are compatible with planar nanotechnologies and thus mass production, which platforms the properties of a metamaterial into a 2D sheet. In the linear regime, wavefront manipulation for lensing, holography, and polarization control has been achieved recently. Interest in metasurfaces operating in the nonlinear regime has also increased due to the ability of metasurfaces to efficiently convert incident light into harmonic frequencies with unusual polarization properties. However, to date, the nonlinear absorption of metasurfaces has been mostly ignored. Here, we demonstrate that plasmonic metasurfaces behave as saturable absorbers with modulation performances superior to the modulation performance of other 2D materials and exhibit unusual polarimetric nonlinear transfer functions. We quantify the link between saturable absorption, the plasmonic resonances of the unit cell and their distribution in a 2D metasurface, and finally provide a practical implementation by integrating the metasurfaces into a fiber laser cavity operating in pulsed regimes driven by the metasurface properties. As such, this work provides new perspectives on ultrathin nonlinear saturable absorbers for applications where tunable nonlinear transfer functions are needed, such as in ultrafast lasers or neuromorphic circuits.