Browsing by Author "Anlage, Steven M."
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Item Deep Wavefront Shaping: Neural Network Enabled Wavefront Reconstruction of Complex Scattering Responses with a Programmable Metasurface}(2021) Frazier, Benjamin W.; Antonsen, Thomas M. Jr; Anlage, Steven M.; Ott, EdwardItem Measuring the Complex Optical Conductivity of Graphene by Fabry-Pérot Reflectance Spectroscopy(Nature Publishing Group, 2016-09-29) Ghamsari, Behnood G.; Tosado, Jacob; Yamamoto, Mahito; Fuhrer, Michael S.; Anlage, Steven M.We have experimentally studied the dispersion of optical conductivity in few-layer graphene through reflection spectroscopy at visible wavelengths. A laser scanning microscope (LSM) with a supercontinuum laser source measured the frequency dependence of the reflectance of exfoliated graphene flakes, including monolayer, bilayer and trilayer graphene, loaded on a Si/SiO2 Fabry-Pérot resonator in the 545–700 nm range. The complex refractive index of few-layer graphene, n − ik, was extracted from the reflectance contrast to the bare substrate. It was found that each few-layer graphene possesses a unique dispersionless optical index. This feature indicates that the optical conductivity does not simply scale with the number of layers, and that inter-layer electrodynamics are significant at visible energies.Item Perfect absorption in complex scattering systems with or without hidden symmetries(Springer Nature, 2020-11-17) Chen, Lei; Kottos, Tsampikos; Anlage, Steven M.Wavefront shaping (WFS) schemes for efficient energy deposition in weakly lossy targets is an ongoing challenge for many classical wave technologies relevant to next-generation telecommunications, long-range wireless power transfer, and electromagnetic warfare. In many circumstances these targets are embedded inside complicated enclosures which lack any type of (geometric or hidden) symmetry, such as complex networks, buildings, or vessels, where the hypersensitive nature of multiple interference paths challenges the viability of WFS protocols. We demonstrate the success of a general WFS scheme, based on coherent perfect absorption (CPA) electromagnetic protocols, by utilizing a network of coupled transmission lines with complex connectivity that enforces the absence of geometric symmetries. Our platform allows for control of the local losses inside the network and of the violation of time-reversal symmetry via a magnetic field; thus establishing CPA beyond its initial concept as the time-reversal of a laser cavity, while offering an opportunity for better insight into CPA formation via the implementation of semiclassical tools.Item Realization and Modeling of Metamaterials Made of rf Superconducting Quantum-Interference Devices(American Physical Society, 2013-12-18) Trepanier, M.; Zhang, Daimeng; Mukhanov, Oleg; Anlage, Steven M.We have prepared meta-atoms based on radio-frequency superconducting quantum-interference devices (rf SQUIDs) and examined their tunability with dc magnetic field, rf current, and temperature. rf SQUIDs are superconducting split-ring resonators in which the usual capacitance is supplemented with a Josephson junction, which introduces strong nonlinearity in the rf properties. We find excellent agreement between the data and a model that regards the Josephson junction as the resistively and capacitively shunted junction. A magnetic field tunability of 80 THz=G at 12 GHz is observed, a total tunability of 56% is achieved, and a unique electromagnetically induced transparency feature at intermediate excitation powers is demonstrated for the first time. An rf SQUID metamaterial is shown to have qualitatively the same behavior as a single rf SQUID with regard to dc flux and temperature tuning.Item Tunable Broadband Transparency of Macroscopic Quantum Superconducting Metamaterials(American Physical Society, 2015-12-18) Zhang, Daimeng; Trepanier, Melissa; Mukhanov, Oleg; Anlage, Steven M.Narrow-band invisibility in an otherwise opaque medium has been achieved by electromagnetically induced transparency (EIT) in atomic systems. The quantum EIT behavior can be classically mimicked by specially engineered metamaterials via carefully controlled interference with a “dark mode.” However, the narrow transparency window limits the potential applications that require a tunable wideband transparent performance. Here, we present a macroscopic quantum superconducting metamaterial with manipulative self-induced broadband transparency due to a qualitatively novel nonlinear mechanism that is different from conventional EIT or its classical analogs. A near-complete disappearance of resonant absorption under a range of applied rf flux is observed experimentally and explained theoretically. The transparency comes from the intrinsic bistability of the meta-atoms and can be tuned on and off easily by altering rf and dc magnetic fields, temperature, and history. Hysteretic in situ 100% tunability of transparency paves the way for autocloaking metamaterials, intensity-dependent filters, and fast-tunable power limiters.Item Tunable Superconducting Josephson Dielectric Metamaterial(American Institute of Physics, 2019-10-28) Trepanier, M.; Zhang, Daimeng; Filippenko, L. V.; Koshelets, V. P.; Anlage, Steven M.We demonstrate a low-dissipation dielectric metamaterial with tunable properties based on the Josephson effect. Superconducting wires loaded with regularly spaced Josephson junctions (critical current Ic ≈ 0.25 μA) spanning a K-band waveguide and aligned with the microwave electric fields create a superconducting dielectric metamaterial. Applied dc current tunes the cutoff frequency and effective permittivity of this unique electric metamaterial. The results are in agreement with an analytical model for microwave transmission through the artificial dielectric medium.