arXiv subjects

Artur R. Davoyan

Publications and source records attributed to Artur R. Davoyan.

At least 19 recordsLinked to original sources

arXiv2024

Nonlinear van der Waals metasurfaces with resonantly enhanced light generation

Efficient nonlinear wave mixing is of paramount importance for a wide range of applications. However, weak optical nonlinearities pose significant challenges for accessing nonlinear light-matter interaction in compact systems. Here, we experimentally study second harmonic generation in deeply subwavelength 3R-MoS2 metasurfaces (<λ/13 thick). Our measurements, supported by theoretical analysis, reveal a complex interplay and coupling between geometric resonances, optical extinction, and strong nonlinear susceptibility dispersion near excitons. We further demonstrate >150-fold enhancement in second harmonic signal at 740 nm driven by the A exciton resonance. Additionally, our theoretical studies predict an enhancement of more than 10^6 in second harmonic generation in <100 nm thick structures exhibiting bound states in the continuum resonance. These findings provide insight into accessing and harnessing the unprecedented 3R-MoS2 nonlinearities at a subwavelength scale, paving the way for ultracompact nonlinear photonic devices.

physics.optics↗

arXiv2023

Near-unity light-matter interaction in mid-infrared van der Waals nanocavities

Accessing mid-infrared radiation is of great importance for a range of applications, including thermal imaging, sensing, and radiative cooling. Here, we study light interaction with hexagonal boron nitride nanocavities and reveal strong and tunable resonances across its hyperbolic transition. In addition to conventional phonon-polariton excitations, we demonstrate that the high refractive index of hexagonal boron nitride outside the Reststrahlen band allows enhanced light-matter interactions in deep subwavelength (<λ/15) nanostructures across a broad 7-8 μm range. Near-unity absorption and high quality (Q>80) resonance interaction in the vicinity of the transverse optical phonon is observed. Our study provides new avenues to design highly efficient and ultracompact structures for controlling mid-infrared radiation and accessing strong light-matter interaction.

physics.optics↗

arXiv2023

Anomalous Reflection Under Ambient Sunlight: Accessing In-Plane Radiation Pressure for Solar Sailing

Harnessing solar radiation pressure is key to transforming space exploration with multiple low cost sunlight propelled spacecraft to outer reaches of space. By controlling the direction of sunlight momentum transfer new missions and better maneuvering in space can be accessed. Here, we discuss design principles for taming in-plane radiation pressure under ambient sunlight. We propose and study theoretically ultra-wideband polarization insensitive metasurfaces for anomalous light reflection. Our design based on segmented tapered patch nanoantenna arrays allows reflection of >60% into one diffraction orders over a 400 nm band across larger part of the solar spectrum. Owing to a wideband nature and polarization insensitivity, our structures convert incident radiation into in-plane radiation pressure force with almost 30% efficiency. We discuss applications of our design to controlling solar sail spin. Beyond solar sailing, we envision that such anomalous metasurfaces for ambient sunlight will find use in solar concentration, spectrum splitting, and solar fuels.

astro-ph.IM↗

arXiv2023

Exciton Assisted Deeply Subwavelength Nano-Photonics

The wave nature of light sets a fundamental diffraction limit that challenges confinement and control of light in nanoscale structures with dimensions significantly smaller than the wavelength. Here, we demonstrate van der Waals MoS_2 nano-photonic devices with dimensions as small as ~ λ/16 (~60 nm at 1000 nm excitation wavelength). This deep subwavelength light confinement is achieved by exploiting the coupling between MoS_2 excitons and photons. We validate deep subwavelength light control via far- and near-field measurements. Our near-field measurements reveal detailed imaging of excitation, evolution, and guidance of fields in MoS_2 nanodevices, whereas our far-field study examines highly confined integrated photonics. Exciton-driven nano-photonics at a fraction of a wavelength demonstrated here could dramatically reduce the size of integrated photonic devices and opto-electronic circuits with potential applications in optical information science and engineering.

physics.optics↗

arXiv2022

Atomic-Void van der Waals Channel Waveguides

Layered van der Waals materials offer a unique platform for creating atomic-void channels with sub-nanometer dimensions. Coupling light into these channels may further advance sensing, quantum information, and single molecule chemistries. Here we examine limits of light guiding in atomic-void channels and show that van der Waals materials exhibiting strong resonances - excitonic and polaritonic - are ideally suited for deeply subwavelength light guiding. We demonstrate that excitonic transition metal dichalcogenides can squeeze > 70% of optical power in just < λ/100 thick channel in the visible and near-infrared. We also show that polariton resonances of hexagonal boron nitride allow deeply subwavelength (< λ/500) guiding in the mid-infrared. We further reveal effects of natural material anisotropy and discuss the influence of losses. Our analysis shows van der Waals channel waveguides while offering extreme optical confinement exhibit significantly lower loss compared to plasmonic counterparts. Such atomic void waveguides pave the way to low loss and deeply subwavelength optics.

physics.optics↗

arXiv2022

A Fast Response Mission to Rendezvous with an Interstellar Object

A solar sail propelled small satellite mission concept to intercept and potentially rendezvous with newly discovered transient interstellar objects (ISOs) is described. The mission concept derives from the proposal for a technology demonstration mission for exiting the solar system at high velocity, eventually to reach the focal region of the solar gravitational lens. The ISO mission concept is to fly a solar sail toward a holding orbit around the Sun and when the ISO orbit is confirmed, target the sailcraft to reach an escape velocity of over 6 AU/year. This would permit rapid response to a new ISO discovery and an intercept within 10 AU from the Sun. Two new proven interplanetary technologies are utilized to enable such a mission: i) interplanetary smallsats, such as those demonstrated by the MarCO mission, and ii) solar sails, such as demonstrated by LightSail and IKAROS missions and developed for NEA Scout and Solar Cruiser missions. Current technology work suggests that already within this decade such a mission could fly and reach an ISO moving through the solar system. It might enable the first encounter with an ISO to allow for imaging and spectroscopy, measurements of size and mass, potentially giving a unique information about the object's origin and composition. A similar approach may be used to allow for a sample return.

astro-ph.IM↗

arXiv2021

A Mission to Nature's Telescope for High-Resolution Imaging of an Exoplanet

The solar gravitational lens (SGL) provides a factor of $10^{11}$ amplification for viewing distant point sources beyond our solar system. As such, it may be used for resolved imaging of extended sources, such as exoplanets, not possible otherwise. To use the SGL, a spacecraft carrying a modest telescope and a coronagraph must reach the SGLs focal region, that begins at $\sim$550 astronomical units (AU) from the Sun and is oriented outward along the line connecting the distant object and the Sun. No spacecraft has ever reached even a half of that distance; and to do so within a reasonable mission lifetime (e.g., less than 25 years) and affordable cost requires a new type of mission design, using solar sails and microsats ($<100$~kg). The payoff is high -- using the SGL is the only practical way we can ever get a high-resolution, multi-pixel image of an Earth-like exoplanet, one that we identify as potentially habitable. This paper describes a novel mission design starting with a rideshare launch from the Earth, spiraling in toward the Sun, and then flying around it to achieve solar system exit speeds of over $20$ AU/year. A new sailcraft design is used to make possible high area to mass ratio for the sailcraft. The mission design enables other fast solar system missions, starting with a proposed very low cost technology demonstration mission (TDM) to prove the functionality and operation of the microsat-solar sail design and then, building on the TDM, missions to explore distant regions of the solar system, and those to study Kuiper Belt objects (KBOs) and the recently discovered interstellar objects (ISOs) are also possible.

astro-ph.IM↗

arXiv2021

A Framework for Discovering Optimal Solutions in Photonic Inverse Design

Photonic inverse design has emerged as an indispensable engineering tool for complex optical systems. In many instances it is important to optimize for both material and geometry configurations, which results in complex non-smooth search spaces with multiple local minima. Finding solutions approaching global optimum may present a computationally intractable task. Here, we develop a framework that allows expediting the search of solutions close to global optimum on complex optimization spaces. We study the way representative black box optimization algorithms work, including genetic algorithm (GA), particle swarm optimization (PSO), simulated annealing (SA), and mesh adaptive direct search (NOMAD). We then propose and utilize a two-step approach that identifies best performance algorithms on arbitrarily complex search spaces. We reveal a connection between the search space complexity and algorithm performance and find that PSO and NOMAD consistently deliver better performance for mixed integer problems encountered in photonic inverse design, particularly with the account of material combinations. Our results differ from a commonly anticipated advantage of GA. Our findings will foster more efficient design of photonic systems with optimal performance.

physics.optics↗

arXiv2021

Light-Matter Coupling in Scalable Van der Waals Superlattices

Two-dimensional (2D) crystals have renewed opportunities in design and assembly of artificial lattices without the constraints of epitaxy. However, the lack of thickness control in exfoliated van der Waals (vdW) layers prevents realization of repeat units with high fidelity. Recent availability of uniform, wafer-scale samples permits engineering of both electronic and optical dispersions in stacks of disparate 2D layers with multiple repeating units. We present optical dispersion engineering in a superlattice structure comprised of alternating layers of 2D excitonic chalcogenides and dielectric insulators. By carefully designing the unit cell parameters, we demonstrate > 90 % narrowband absorption in < 4 nm active layer excitonic absorber medium at room temperature, concurrently with enhanced photoluminescence in cm2 samples. These superlattices show evidence of strong light-matter coupling and exciton-polariton formation with geometry-tunable coupling constants. Our results demonstrate proof of concept structures with engineered optical properties and pave the way for a broad class of scalable, designer optical metamaterials from atomically-thin layers.

cond-mat.mtrl-sci↗

arXiv2021

Spatiotemporal Imaging of Thickness-Induced Band Bending Junctions

Van der Waals materials exhibit naturally passivated surfaces and can form versatile heterostructures, enabling observation of carrier transport mechanisms not seen in three-dimensional materials. Here we report observation of a "band bending junction", a new type of semiconductor homojunction whose surface potential landscape depends solely on a difference in thickness between the two semiconductor regions atop a buried heterojunction interface. Using MoS2 on Au to form a buried heterojunction interface, we find that lateral surface potential differences can arise in MoS2 from the local extent of vertical band bending in thin and thick MoS2 regions. Using scanning ultrafast electron microscopy, we examine the spatiotemporal dynamics of photogenerated charge carriers and find that lateral carrier separation is enabled by a band bending junction, which is confirmed with semiconductor transport simulations. Band bending junctions may therefore enable new electronic and optoelectronic devices in Van der Waals materials that rely on thickness variations rather than doping to separate charge carriers.

cond-mat.mes-hall↗

arXiv2020

All van der Waals Integrated Nanophotonics

Integrated optics is at the heart of a wide range of systems from remote sensing and communications to computing and quantum information processing. Demand for smaller and more energy efficient structures stimulates search for more advanced material platforms. Here, we propose a concept of an all van der Waals photonics, where we show that electronically bulk transition metal dichalcogenide (TMDC) semiconductors are well fitted for the design of key optical components for nanoscale and integrated photonics. Specifically, we demonstrate theoretically that owing to low optical loss and high refractive index across near-infrared and telecom frequency bands, components made of bulk TMDCs can potentially outperform counterparts made of conventional 3D semiconductors, such as Si and III/Vs. We discuss several key quantum and classical optical components and show that bulk TMDCs may pave the way to smaller footprint devices, more energy efficient electro-optical modulators, and stronger quantum light-materials interaction. Enhanced optical performance, ease of integration, and a wide selection of materials suggest that bulk TMDCs may complement and, potentially, replace existing integrated photonics systems.

physics.optics↗

arXiv2019

Hybrid Exciton-Plasmon-Polaritons in van der Waals Semiconductor Gratings

Van der Waals materials and heterostructures manifesting strongly bound room temperature exciton states exhibit emergent physical phenomena and are of a great promise for optoelectronic applications. Here, we demonstrate that nanostructured multilayer transition metal dichalcogenides by themselves provide an ideal platform for excitation and control of excitonic modes, paving the way to exciton-photonics. Hence, we show that by patterning the TMDCs into nanoresonators, strong dispersion and avoided crossing of excitons and hybrid polaritons with interaction potentials exceeding 410 meV may be controlled with great precision. We further observe that inherently strong TMDC exciton absorption resonances may be completely suppressed due to excitation of hybrid photon states and their interference. Our work paves the way to a next generation of integrated exciton optoelectronic nano-devices and applications in light generation, computing, and sensing.

cond-mat.mes-hall↗

arXiv2017

Van der Waals Materials for Atomically-Thin Photovoltaics: Promise and Outlook

Two-dimensional (2D) semiconductors provide a unique opportunity for optoelectronics due to their layered atomic structure, electronic and optical properties. To date, a majority of the application-oriented research in this field has been focused on field-effect electronics as well as photodetectors and light emitting diodes. Here we present a perspective on the use of 2D semiconductors for photovoltaic applications. We discuss photonic device designs that enable light trapping in nanometer-thickness absorber layers, and we also outline schemes for efficient carrier transport and collection. We further provide theoretical estimates of efficiency indicating that 2D semiconductors can indeed be competitive with and complementary to conventional photovoltaics, based on favorable energy bandgap, absorption, external radiative efficiency, along with recent experimental demonstrations. Photonic and electronic design of 2D semiconductor photovoltaics represents a new direction for realizing ultrathin, efficient solar cells with applications ranging from conventional power generation to portable and ultralight solar power.

physics.optics↗

arXiv2017

Purcell Enhancement of Parametric Luminescence: Bright and Broadband Nonlinear Light Emission in Metamaterials

Single-photon and correlated two-photon sources are important elements for optical information systems. Nonlinear downconversion light sources are robust and stable emitters of single photons and entangled photon pairs. However, the rate of downconverted light emission, dictated by the properties of low-symmetry nonlinear crystals, is typically very small, leading to significant constrains in device design and integration. In this paper, we show that the principles for spontaneous emission control (i.e. Purcell effect) of isolated emitters in nanoscale structures, such as metamaterials, can be generalized to describe the enhancement of nonlinear light generation processes such as parametric down conversion. We develop a novel theoretical framework for quantum nonlinear emission in a general anisotropic, dispersive and lossy media. We further find that spontaneous parametric downconversion in media with hyperbolic dispersion is broadband and phase-mismatch-free. We predict a 1000-fold enhancement of the downconverted emission rate with up to 105 photon pairs per second in experimentally realistic nanostructures. Our theoretical formalism and approach to Purcell enhancement of nonlinear optical processes, provides a framework for description of quantum nonlinear optical phenomena in complex nanophotonic structures.

physics.optics↗

arXiv2017

High Photovoltaic Quantum Efficiency in Ultrathin van der Waals Heterostructures

We report experimental measurements for ultrathin (< 15 nm) van der Waals heterostructures exhibiting external quantum efficiencies exceeding 50%, and show that these structures can achieve experimental absorbance > 90%. By coupling electromagnetic simulations and experimental measurements, we show that pn WSe2/MoS2 heterojunctions with vertical carrier collection can have internal photocarrier collection efficiencies exceeding 70%.

cond-mat.mes-hall↗

arXiv2016

Gate-Variable Mid-Infrared Optical Transitions in a $(Bi_{1-x}Sb_x)_2Te_3$ Topological Insulator

We report mid-infrared spectroscopy measurements of an electrostatically gated topological insulator, in which we observe several percent modulation of transmittance and reflectance of (Bi1-xSbx)2Te3 films as gating shifts the Fermi level. Infrared transmittance measurements of gated (Bi1-xSbx)2Te3 films were enabled by use of an epitaxial lift-off method for large-area transfer of topological insulator films from infrared-absorbing SrTiO3 growth substrates to thermal oxidized silicon substrates. We combine these optical experiments with transport measurements and angle-resolved photoemission spectroscopy to identify the observed spectral modulation as a gate-driven transfer of spectral weight between both bulk and topological surface channels and interband and intraband channels. We develop a model for the complex permittivity of gated (Bi1-xSbx)2Te3, and find a good match to our experimental data. These results open the path for layered topological insulator materials as a new candidate for tunable infrared optics and highlight the possibility of switching topological optoelectronic phenomena between bulk and spin-polarized surface regimes.

cond-mat.mes-hall↗

arXiv2016

Near Unity Absorption in Van der Waals Semiconductors for Ultrathin Optoelectronics

We demonstrate near unity, broadband absorbing optoelectronic devices using sub-15 nm thick transition metal dichalcogenides (TMDCs) of molybdenum and tungsten as van der Waals semiconductor active layers. Specifically, we report that near-unity light absorption is possible in extremely thin (< 15 nm) Van der Waals semiconductor structures by coupling to strongly damped optical modes of semiconductor/metal heterostructures. We further fabricate Schottky junction devices using these highly absorbing heterostructures and characterize their optoelectronic performance. Our work addresses one of the key criteria to enable TMDCs as potential candidates to achieve high optoelectronic efficiency.

cond-mat.mtrl-sci↗

arXiv2012

Nonreciprocal rotating power flow within plasmonic nanostructures

We theoretically explore the notion of nonreciprocal near-zone manipulation of electromagnetic fields within subwavelength plasmonic nanostructures embedded in magneto-optical materials. We derive an analytical model predicting a strong, magneto-optically induced time-reversal symmetry breaking of localized plasmonic resonances in topologically symmetric structures. Our numerical simulations of plasmon excitations reveal a considerable near-zone power flow rotation within such hybrid nanostructures, demonstrating nanoscale nonreciprocity. This can be considered as another mechanism for tuning plasmonic phenomena at the nanoscale.

physics.optics↗