Abstract-Nonlinearity in the Dark: Broadband Terahertz Generation with Extremely High Efficiency

Ming Fang, Nian-Hai Shen, Wei E. I. Sha, Zhixiang Huang, Thomas Koschny, and Costas M. Soukoulis

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.027401

Plasmonic metamaterials and metasurfaces offer new opportunities in developing high performance terahertz emitters and detectors beyond the limitations of conventional nonlinear materials. However, simple meta-atoms for second-order nonlinear applications encounter fundamental trade-offs in the necessary symmetry breaking and local-field enhancement due to radiation damping that is inherent to the operating resonant mode and cannot be controlled separately. Here we present a novel concept that eliminates this restriction obstructing the improvement of terahertz generation efficiency in nonlinear metasurfaces based on metallic nanoresonators. This is achieved by combining a resonant dark-state metasurface, which locally drives nonlinear nanoresonators in the near field, with a specific spatial symmetry that enables destructive interference of the radiating linear moments of the nanoresonators, and perfect absorption via simultaneous electric and magnetic critical coupling of the pump radiation to the dark mode. Our proposal allows eliminating linear radiation damping, while maintaining constructive interference and effective radiation of the nonlinear components. We numerically demonstrate a giant second-order nonlinear susceptibility $\sim {10}^{-11}m/V$, a one order improvement compared with the previously reported split-ring-resonator metasurface, and correspondingly, a 2 orders of magnitude enhanced terahertz energy extraction should be expected with our configuration under the same conditions. Our study offers a paradigm of high efficiency tunable nonlinear metadevices and paves the way to revolutionary terahertz technologies and optoelectronic nanocircuitry.

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Abstract-Terahertz polarization converter based on all-dielectric high birefringence metamaterial with elliptical air holes

Jianchen Zi, Quan Xu, Qiu Wang, Chunxiu Tian, Yanfeng Li, Xixiang Zhang, Jiaguang Han, Weili Zhang

https://www.sciencedirect.com/science/article/pii/S0030401818301007

Metamaterials have been widely applied in the polarization conversion of terahertz (THz) waves. However, common plasmonic metamaterials usually work as reflective devices and have low transmissions. All-dielectric metamaterials can overcome these shortcomings. An all-dielectric metamaterial based on silicon with elliptical air holes is reported to achieve high artificial birefringence at THz frequencies. Simulations show that with appropriate structural parameters the birefringence of the dielectric metamaterial can remain flat and is above 0.7 within a broad band. Moreover, the metamaterial can be designed as a broadband quarter wave plate. A sample metamaterial was fabricated and tested to prove the validity of the simulations, and the sample could work as a quarter wave plate at 1.76 THz. The all-dielectric metamaterial that we proposed is of great significance for high performance THz polarization converters.

Abstract-Extreme sensitive metasensor for targeted biomarkers identification using colloidal nanoparticles-integrated plasmonic unit cells

Arash Ahmadivand, Burak Gerislioglu, Asahi Tomitaka, Pandiaraj Manickam, Ajeet Kaushik, Shekhar Bhansali, Madhavan Nair, and Nezih Pala

https://www.osapublishing.org/boe/abstract.cfm?uri=boe-9-2-373&origin=search

Engineered terahertz (THz) plasmonic metamaterials have emerged as promising platforms for quick infection diagnosis, cost-effective and real-time pharmacology applications owing to their non-destructive and harmless interaction with biological tissues in both in vivo and in vitroassays. As a recent member of THz metamaterials family, toroidal metamaterials have been demonstrated to be supporting high-quality sharp resonance modes. Here we introduce a THz metasensor based on a plasmonic surface consisting of metamolecules that support ultra-narrow toroidal resonances excited by the incident radiation and demonstrate detection of an ultralow concertation targeted biomarker. The toroidal plasmonic metasurface was designed and optimized through extensive numerical studies and fabricated by standard microfabrication techniques. The surface then functionalized by immobilizing the antibody for virus-envelope proteins (ZIKV-EPs) for selective sensing. We sensed and quantified the ZIKV-EP in the assays by measuring the spectral shifts of the toroidal resonances while varying the concentration. In an improved protocol, we introduced gold nanoparticles (GNPs) decorated with the same antibodies onto the metamolecules and monitored the resonance shifts for the same concentrations. Our studies verified that the presence of GNPs enhances capturing of biomarker molecules in the surrounding medium of the metamaterial. By measuring the shift of the toroidal dipolar momentum (up to Δω~0.35 cm−1) for different concentrations of the biomarker proteins, we analyzed the sensitivity, repeatability, and limit of detection (LoD) of the proposed toroidal THz metasensor. The results show that up to 100-fold sensitivity enhancement can be obtained by utilizing plasmonic nanoparticles-integrated toroidal metamolecules in comparison to analogous devices. This approach allows for detection of low molecular-weight biomolecules (≈13 kDa) in diluted solutions using toroidal THz plasmonic unit cells.

© 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Defect-Induced Fano Resonances in Corrugated Plasmonic Metamaterials

http://onlinelibrary.wiley.com/doi/10.1002/adom.201600960/abstract

A novel defect-induced planar meta-atom that supports multiple Fano resonances in a defective corrugated metallic disk (CMD) structure is proposed. Numerical and experimental results reveal that multiple Fano resonances can be excited at terahertz frequencies when the symmetry of the CMD is broken by introducing a small angular defect. These multiple Fano resonances result from mutual coupling between the bright dipolar mode evoked by the edge of the wedge-shaped slice and dark multipole spoof localized surface plasmon modes. Furthermore, the influence of the angle of defect on the Q-factor and the resonance intensity of the quadrupolar resonance peak is investigated. Large values of figure of merit are obtained due to higher Fano resonance intensity and Q-factor. Results from two defective slices in the CMD structure validate the mechanism of the observed phenomenon. The findings of this work would enable a defect-induced Fano resonance platform for biosensing, terahertz domain filtering, and strong light–matter interactions.