Showing papers by "Nader Engheta published in 2023"
Peer Review•
13 Jan 2023
TL;DR: The role of structured wave fields in various areas of wave physics is surveyed in this paper , where the role of wave fields with inhomogeneities in the amplitude, phase, and polarization is discussed.
Abstract: Structured waves are ubiquitous for all areas of wave physics, both classical and quantum, where the wavefields are inhomogeneous and cannot be approximated by a single plane wave. Even the interference of two plane waves, or a single inhomogeneous (evanescent) wave, provides a number of nontrivial phenomena and additional functionalities as compared to a single plane wave. Complex wavefields with inhomogeneities in the amplitude, phase, and polarization, including topological structures and singularities, underpin modern nanooptics and photonics, yet they are equally important, e.g., for quantum matter waves, acoustics, water waves, etc. Structured waves are crucial in optical and electron microscopy, wave propagation and scattering, imaging, communications, quantum optics, topological and non-Hermitian wave systems, quantum condensed-matter systems, optomechanics, plasmonics and metamaterials, optical and acoustic manipulation, and so forth. This Roadmap is written collectively by prominent researchers and aims to survey the role of structured waves in various areas of wave physics. Providing background, current research, and anticipating future developments, it will be of interest to a wide cross-disciplinary audience.
3 citations
TL;DR: In this paper , the dimension of "time" is introduced into material parameters, which can change with time in addition to (or instead of ) their variation in three-dimensional (3D) space.
Abstract: Description Optical platforms using material parameters that change with time have diverse applications For optics, like semiconductor heterostructures, the interfaces and inhomogeneities in materials can manipulate optical waves and fields. Numerous photonic devices and components—for example, waveguides, lenses, and cavities—function owing to the presence of such interfaces and material spatial variations. Such parameter inhomogeneity is generally in three dimensions of space (spatial inhomogeneities). But what if the dimension of “time” could be introduced into material parameters? This would mean that parameters can change with time in addition to (or instead of ) their variation in three-dimensional (3D) space. Such 4D material platforms for optics (or for any other wave and field phenomena) offer additional degrees of freedom in manipulating light–matter interaction, providing exciting opportunities such as in new approaches to frequency manipulation, signal amplification, and beam forming.
3 citations
07 Apr 2023
TL;DR: In this paper , the authors introduce a mechanism that can both hold and amplify electromagnetic waves by rapidly changing the permittivity of the medium during the wave travel from a positive to a dispersionless (i.e., non-Foster) negative value and then back again.
Abstract: We introduce a mechanism that can both hold and amplify electromagnetic waves by rapidly changing the permittivity of the medium during the wave travel from a positive to a dispersionless (i.e. non-Foster) negative value and then back again. The underlying physics behind this phenomenon is theoretically explored by considering a plane wave in an unbounded medium. Interestingly, we show that a rapid positive-to-negative temporal change of {\epsilon}(t) causes the propagation of the wave to stop (observed by a frozen phase in time) while the amplitude of the frozen field exponentially grows. Stepping the permittivity back to the original (or a new) positive value will cause the wave to thaw and resume propagation with the original (or the new) frequency, respectively. We numerically study the case of dipole radiation in such time-varying non-Foster structures. As a possible implementation, we propose a parallel plate waveguide platform loaded with time-dependent media emulating parallel lumped non-Foster negative capacitors. Such non-Foster time-varying structures may open new venues in controlling and manipulating wave-matter interaction.
2 citations
TL;DR: In this paper , a top-down lithographic patterning and deposition process is reported for producing nanoparticles (NPs) with well-defined sizes, shapes, and compositions that are often not accessible by wet-chemical synthetic methods.
Abstract: A top-down lithographic patterning and deposition process is reported for producing nanoparticles (NPs) with well-defined sizes, shapes, and compositions that are often not accessible by wet-chemical synthetic methods. These NPs are ligated and harvested from the substrate surface to prepare colloidal NP dispersions. Using a template-assisted assembly technique, fabricated NPs are driven by capillary forces to assemble into size- and shape-engineered templates and organize into open or close-packed multi-NP structures or NP metamolecules. The sizes and shapes of the NPs and of the templates control the NP number, coordination, interparticle gap size, disorder, and location of defects such as voids in the NP metamolecules. The plasmonic resonances of polygonal-shaped Au NPs are exploited to correlate the structure and optical properties of assembled NP metamolecules. Comparing open- and close-packed architectures highlights that introduction of a center NP to form closed-packed assemblies supports collective interactions, altering magnetic optical modes and multipolar interactions in Fano resonances. Decreasing the distance between NPs strengthens the plasmonic coupling, and the structural symmetries of the NP metamolecules determine the orientation-dependent scattering response. This article is protected by copyright. All rights reserved.
1 citations
01 Feb 2023
TL;DR: U.S.A. as mentioned in this paper , U.S., USA, USA, 2003, p. 7, 6, 7, 9, 1, 6.1, 2
Abstract: U.S.A
TL;DR: Temporal modulation of material parameters provides a new degree of freedom for metamaterials, metasurfaces and wave-matter interactions as a whole as mentioned in this paper , which can lead to novel physical effects with potential applications.
Abstract: Temporal modulation of material parameters provides a new degree of freedom for metamaterials, metasurfaces and wave-matter interactions as a whole. In time-varying media the electromagnetic energy may not be conserved, and the time reversal symmetry may be broken, which may lead to novel physical effects with potential applications. Currently, theoretical and experimental aspects of this field are rapidly advancing, expanding our understanding of wave propagation in such complex spatiotemporal platforms. This field promises novel possibilities and directions in research, innovation and exploration.
TL;DR: In this paper , a general effective medium theory that combines spatial multilayered media with temporal multistepped changes of the permittivity is proposed, which represents a combination of spatial and temporal inhomogeneities in a single structure.
Abstract: While wave-matter interactions can be tailored in space via spatial inhomogeneities in material parameters, temporal and spacetime media are becoming increasingly popular as they may enable the full control of electromagnetic (EM) waves in four dimensions (4D). Here, expanding our previous work on the effective medium concept of temporal media, we develop more general effective medium theories that combine spatial multilayered media with temporal multistepped changes of the permittivity. This work represents a combination of spatial and temporal inhomogeneities in a single structure. As the temporal modulation is applied within certain spatial multilayers (not all the layers), our approach may relax the need for temporally modulating the whole medium where the wave travels while still achieving frequency conversion (a key feature of temporal multistepped media). The theoretical formulation and closed-form expressions for the effective permittivity of such spacetime effective media are presented. The proposed structure is studied via numerical simulations, demonstrating the possibility of designing spacetime effective media using a combination of temporally and spatially modulated materials. The increased degrees of freedom provided by our approach may open new possibilities for manipulating wave-matter interaction in 4D.
TL;DR: In this paper , the authors developed a formulation governing the rest frame electrodynamics in rotating electromagnetic systems and circuits, which revealed new rotation-induced effects such as fictitious charges, gain, energy harvesting, and new device functionalities, e.g., positive or negative memristors and their dualities.
Abstract: The omnipresence of rotation, often observed in its own rest frame of reference, profoundly affects human experience, science and technology. Here, the authors develop a formulation governing the rest frame electrodynamics in rotating electromagnetic systems and circuits. This study reveals new rotation-induced effects such as fictitious charges, gain, energy harvesting, and new device functionalities, e.g., positive or negative memristors and their dualities. These effects may potentially offer pathways to new technologies and materials.