Dynamic control and manipulation of near-fields using direct feedback.

Shaping and controlling electromagnetic fields at the nanoscale is vital for advancing efficient and compact devices used in optical communications, sensing and metrology, as well as for the exploration of fundamental properties of light-matter interaction and optical nonlinearity. Real-time feedback for active control over light can provide a significant advantage in these endeavors, compensating for ever-changing experimental conditions and inherent or accumulated device flaws. Scanning nearfield microscopy, being slow in essence, cannot provide such a real-time feedback that was thus far possible only by scattering-based microscopy.

Topological Transitions and Surface Umklapp Scattering in Weakly Modulated Periodic Metasurfaces.

Controlling and manipulating surface waves is highly beneficial for imaging applications, nanophotonic device design, and light-matter interactions. While deep-subwavelength structuring of the metal-dielectric interface can influence surface waves by forming strong effective anisotropy, it disregards important structural degrees of freedom such as the interplay between corrugation periodicity and depth and its effect on the beam transport. Here, we unlock these degrees of freedom, introducing weakly modulated metasurfaces, structured metal-dielectric surfaces beyond effective medium.

Nonlinear Forced Response of Plasmonic Nanostructures.

Incorporating optical surface waves in nonlinear processes unlocks unique and sensitive nonlinear interactions wherein highly confined surface states can be accessed and explored. Here, we unravel the rich physics of modal-nonmodal state pairs of short-range surface plasmons in thin metal films by leveraging "dark nonlinearity"-a nonradiating nonlinear source. We control and observe the nonlinear forced response of these modal-nonmodal pairs and present nonlinearly mediated direct access to nonmodal plasmons in a lossless regime.

Emulating spin transport with nonlinear optics, from high-order skyrmions to the topological Hall effect.

Exploring material magnetization led to countless fundamental discoveries and applications, culminating in the field of spintronics. Recently, research effort in this field focused on magnetic skyrmions - topologically robust chiral magnetization textures, capable of storing information and routing spin currents via the topological Hall effect. In this article, we propose an optical system emulating any 2D spin transport phenomena with unprecedented controllability, by employing three-wave mixing in 3D nonlinear photonic crystals.

Miniaturizing nanoantennas with hybrid photonic-plasmonic modes for improved metasurfaces.

The increasing interest in manipulating light on scales much smaller than its wavelength has driven intensive research on designing high efficiency optical antennas for near and far field applications. In particular, such nanoantennas serve as the main building block of metasurfaces, which were identified as an emerging technology for their capability in constructing versatile optical and electromagnetic devices. Hence, reducing the antennas' dimensions without compromising on their scattering efficiency is of utmost importance.

Spin-Orbit Interaction of Light in Plasmonic Lattices.

In the past decade, the spin-orbit interaction (SOI) of light has been a driving force in the design of metamaterials, metasurfaces, and schemes for light-matter interaction. A hallmark of the spin-orbit interaction of light is the spin-based plasmonic effect, converting spin angular momentum of propagating light to near-field orbital angular momentum. Although this effect has been thoroughly investigated in circular symmetry, it has yet to be characterized in a noncircular geometry, where whirling, periodic plasmonic fields are expected.

Observation of Anderson localization in disordered nanophotonic structures.

Anderson localization is an interference effect crucial to the understanding of waves in disordered media. However, localization is expected to become negligible when the features of the disordered structure are much smaller than the wavelength. Here we experimentally demonstrate the localization of light in a disordered dielectric multilayer with an average layer thickness of 15 nanometers, deep into the subwavelength regime.

Double moiré structured illumination microscopy with high-index materials.

Structured illumination microscopy utilizes illumination of periodic light patterns to allow reconstruction of high spatial frequencies, conventionally doubling the microscope's resolving power. This Letter presents a structured illumination microscopy scheme with the ability to achieve 60 nm resolution by using total internal reflection of a double moiré pattern in high-index materials. We propose a realization that provides dynamic control over relative amplitudes and phases of four coherently interfering beams in gallium phosphide and numerically demonstrate its capability.

Linearly dichroic plasmonic lens and hetero-chiral structures.

We present an experimental study of Hetero-Chiral (HC) plasmonic lenses, comprised of constituents with opposite chirality, demonstrating linearly dichroic focusing. The lenses focus only light with a specific linear polarization and result in a dark focal spot for the orthogonal polarization state. We introduce the design concepts and quantitatively compare several members of the HC family, deriving necessary conditions for linear dichroism and several comparative engineering parameters.

Spin-patterned plasmonics: towards optical access to topological-insulator surface states.

Topological insulators (TI) are new phases of matter with topologically protected surface states (SS) possessing novel physical properties such as spin-momentum locking. Coupling optical angular momentum to the SS is of interest for both fundamental understanding and applications in future spintronic devices. However, due to the nanoscale thickness of the surface states, the light matter interaction is dominated by the bulk.

Metafocusing by a Metaspiral Plasmonic Lens.

We designed and realized a metasurface (manipulating the local geometry) spiral (manipulating the global geometry) plasmonic lens, which fundamentally overcomes the multiple efficiency and functionality challenges of conventional in-plane plasmonic lenses. The combination of spirality and metasurface achieves much more efficient and uniform linear-polarization-independent plasmonic focusing. As for functionality, under matched circularly polarized illumination the lens directs all of the power coupled to surface plasmon polaritons (SPPs) into the focal spot, while the orthogonal polarization excites only diverging SPPs that do not penetrate the interior of the lens, achieving 2 orders of magnitude intensity contrast throughout the entire area of the lens.

Subwavelength multilayer dielectrics: ultrasensitive transmission and breakdown of effective-medium theory.

We show that a purely dielectric structure made of alternating layers of deep subwavelength thicknesses exhibits novel transmission effects which completely contradict conventional effective medium theories exactly in the regime in which those theories are commonly used. We study waves incident at the vicinity of the effective medium's critical angle for total internal reflection and show that the transmission through the multilayer structure depends strongly on nanoscale variations even at layer thicknesses smaller than λ/50. In such deep subwavelength structures, we demonstrate dramatic changes in the transmission for variations in properties such as periodicity, order of the layers, and their parity.

Exact modeling of cylindrical metal-dielectric multilayers beyond the effective medium approximation.

We present a semi-analytical method for accurate modeling of wave propagation in cylindrically symmetric subwavelength metal-dielectric multilayers. Utilizing a cylindrical transfer matrix method, we compute the amplitude transfer function of cylindrical hyperlens, simulate the exact field distribution and propagation for a given source and compare it to that in effective hyperbolic medium. We investigate the conditions under which the effective medium theory (EMT) is valid and show that in cylindrical configuration, a new degree of freedom is present in the applicability of the EMT-the ratio between the inner radius of the structure and the unit cell size.

Field enhancement and resonance phenomena in complex three-dimensional nanoparticles: efficient computation using the source-model technique.

We present a semi-analytical method for computing the electromagnetic field in and around 3D nanoparticles (NP) of complex shape and demonstrate its power via concrete examples of plasmonic NPs that have nonsymmetrical shapes and surface areas with very small radii of curvature. In particular, we show the three axial resonances of a 3D cashew-nut and the broadband response of peanut-shell NPs. The method employs the source-model technique along with a newly developed intricate source distributing algorithm based on the surface curvature.

Plasmon-enhanced four-wave mixing for superresolution applications.

We introduce a nonlinear optical approach to transform spatial information stored in evanescent waves into propagating ones: we study analytically the use of partially degenerate four-wave mixing in thin metallic film to map a band of evanescent waves at a given frequency into a propagating-wave band at a different one. The relatively low efficiency of this process is compensated by setting the pump beam, mediating this transformation, to be a surface plasmon polariton, whose field enhancement increases the nonlinear interaction strength. This setting can be utilized for nonresonant plasmon-assisted superresolution applications that support transverse-electric polarization, in contrast to linear plasmonic imaging (such as superlens) that can only transfer transverse-magnetic waves.

Finite element simulation of a perturbed axial-symmetric whispering-gallery mode and its use for intensity enhancement with a nanoparticle coupled to a microtoroid.

We present an optical mode solver for a whispering gallery resonator coupled to an adjacent arbitrary shaped nano-particle that breaks the axial symmetry of the resonator. Such a hybrid resonator-nanoparticle is similar to what was recently used for bio-detection and for field enhancement. We demonstrate our solver by parametrically studying a toroid-nanoplasmonic device and get the optimal nano-plasmonic size for maximal enhancement.

Nonlinear hyperlens.

The performance of an optical hyperlens made of metal-dielectric layers can be improved by incorporating self-focusing nonlinearity in the dielectric layers. Using a modified beam propagation method in cylindrical coordinates, we show increased bandwidth and better propagation length, which can improve the spatial and temporal resolution of the device.

Anti-Hermitian plasmon coupling of an array of gold thin-film antennas for controlling light at the nanoscale.

Open quantum systems consisting of coupled bound and continuum states have been studied in a variety of physical systems, particularly within the scope of nuclear, atomic, and molecular physics. In the open systems, the effects of the continuum decay channels are accounted for by indirect non-Hermitian couplings among the quasibound states. Here we explore anti-Hermitian coupling in a plasmonic system for spatially manipulating light on the nanoscale.

Optical negative refraction by four-wave mixing in thin metallic nanostructures.

The law of refraction first derived by Snellius and later introduced as the Huygens-Fermat principle, states that the incidence and refracted angles of a light wave at the interface of two different materials are related to the ratio of the refractive indices in each medium. Whereas all natural materials have a positive refractive index and therefore exhibit refraction in the positive direction, artificially engineered negative index metamaterials have been shown capable of bending light waves negatively. Such a negative refractive index is the key to achieving a perfect lens that is capable of imaging well below the diffraction limit.

Design, fabrication and characterization of indefinite metamaterials of nanowires.

Indefinite optical properties, which are typically characterized by hyperbolic dispersion relations, have not been observed in naturally occurring materials, but can be realized through a metamaterial approach. We present here the design, fabrication and characterization of nanowire metamaterials with indefinite permittivity, in which all-angle negative refraction of light is observed. The bottom-up fabrication technique, which applies electrochemical plating of nanowires in porous alumina template, is developed and demonstrated in achieving uniform hyperbolic optical properties at a large scale.

Magnetized plasma for reconfigurable subdiffraction imaging.

We show that magnetized plasma with appropriately designed parameters supports nearly diffractionless propagation of electromagnetic waves along the direction of the applied magnetic field, arising from their unbounded equifrequency contour in the magnetized plasma. Such a unique feature can be utilized to construct subdiffraction imaging devices, which is confirmed by detailed numerical investigations. Subdiffraction imaging devices based on magnetic plasma do not require microfabrication normally entailed by construction of metamaterials; more importantly, they can be dynamically reconfigured by tuning the applied magnetic field or the plasma density, and therefore they represent a facile and powerful route for imaging applications.

Three-dimensional nanometer-scale optical cavities of indefinite medium.

Miniaturization of optical cavities has numerous advantages for enhancing light-matter interaction in quantum optical devices, low-threshold lasers with minimal power consumption, and efficient integration of optoelectronic devices at large scale. However, the realization of a truly nanometer-scale optical cavity is hindered by the diffraction limit of the nature materials. In addition, the scaling of the photon life time with the cavity size significantly reduces the quality factor of small cavities.