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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Predictable third harmonic generation in GaAs metasurfaces through group theory inverse design of meta-atoms

Here we report the group theory-based inverse design of meta-atoms for a dielectric metasurface in GaAs with predictable optical linear response and third harmonic generation (THG). Six sharp Fano resonances have been observed with a corresponding polarization dependence as predicted by group theory and the meta-atom’s symmetry in the D2h point group. THG has been observed for two modes under x-polarization excitation and one mode for y-polarization, in agreement with theoretical symmetry predictions. The polarization-dependent THG aspect ratio was observed to reach as high as 108. Through strategic structural or symmetry-preserving perturbations, it was shown that the THG can be enhanced or reduced by a factor of 7. The highest THG conversion efficiency was estimated to be 3.1×10-7 at the pump intensity of 1.51 MW/cm2. This high THG conversion efficiency indicates that our group theory approach to modal engineering opens a new path towards optical nonlinearity tuning in dielectric metasurfaces.

Aoueille, Andrew↗
DOE OSTI2024

Spinning metasurface stack for spectro-polarimetric thermal imaging

Spectro-polarimetric imaging in the long-wave infrared (LWIR) region plays a crucial role in applications from night vision and machine perception to trace gas sensing and thermography. However, the current generation of spectro-polarimetric LWIR imagers suffers from limitations in size, spectral resolution, and field of view (FOV). While meta-optics-based strategies for spectro-polarimetric imaging have been explored in the visible spectrum, their potential for thermal imaging remains largely unexplored. In this work, we introduce an approach for spectro-polarimetric decomposition by combining large-area stacked meta-optical devices with advanced computational imaging algorithms. The co-design of a stack of spinning dispersive metasurfaces along with compressive sensing and dictionary learning algorithms allows simultaneous spectral and polarimetric resolution without the need for bulky filter wheels or interferometers. Our spinning-metasurface-based spectro-polarimetric stack is compact (<10×10×10cm) and robust, and it offers a wide field of view (20.5°). We show that the spectral resolving power of our system substantially enhances performance in machine learning tasks such as material classification, a challenge for conventional panchromatic thermal cameras. Our approach represents a significant advance in the field of thermal imaging for a wide range of applications including heat-assisted detection and ranging (HADAR).

Optics↗
DOE OSTI2023

Beyond Conventional Sensing: Hybrid Plasmonic Metasurfaces and Bound States in the Continuum

Fano resonances result from the strong coupling and interference between a broad background state and a narrow, almost discrete state, leading to the emergence of asymmetric scattering spectral profiles. Under certain conditions, Fano resonances can experience a collapse of their width due to the destructive interference of strongly coupled modes, resulting in the formation of bound states in the continuum (BIC). In such cases, the modes are simultaneously localized in the nanostructure and coexist with radiating waves, leading to an increase in the quality factor, which is virtually unlimited. In this work, we report on the design of a layered hybrid plasmonic-dielectric metasurface that facilitates strong mode coupling and the formation of BIC, resulting in resonances with a high quality factor. We demonstrate the possibility of controlling Fano resonances and tuning Rabi splitting using the nanoantenna dimensions. We also experimentally demonstrate the generalized Kerker effect in a binary arrangement of silicon nanodisks, which allows for the tuning of the collective modes and creates new photonic functionalities and improved sensing capabilities. Our findings have promising implications for developing plasmonic sensors that leverage strong light-matter interactions in hybrid metasurfaces.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Metasurface-assisted 3D beam shaping for desired phase, amplitude, and polarization

Cascaded metasurfaces can control the phase, amplitude and polarization of an electromagnetic beam, shaping it in three dimensional configuration not achievable with other methods. Each cascaded metasurface has dielectric or metallic scatterers arranged in a period array. The shape of the scatterers determines the three dimensional configuration of the output beam and is determined with iterative calculations through computational simulations.

Kamali, Seyedeh Mahsa↗
DOE OSTI2022

Tunable infrared pixels having unpatterned graphene layer and conductive metasurface

A monolithically integrated, tunable infrared pixel comprises a combined broadband detector and graphene-enabled tunable metasurface filter that operate as a single solid-state device with no moving parts. Functionally, tunability results from the plasmonic properties of graphene that are acutely dependent upon the carrier concentration within the infrared. Voltage induced changes in graphene's carrier concentration can be leveraged to change the metasurface filter's transmission thereby altering the “colors” of light reaching the broadband detector and hence its spectral responsivity. The invention enables spectrally agile infrared detection with independent pixel-to-pixel spectral tunability.

Beechem, III, Thomas Edwin↗
DOE OSTI2023

Birefringent waveplate and method for forming a waveplate having a birefringent metasurface

The present disclosure relates to a waveplate having a substrate forming an optic. The substrate may have an integral portion forming a plurality of angled columnar features on an exposed surface thereof. The plurality of angled columnar features may further be aligned parallel with a directional plane formed non-parallel to a reference plane, with the reference plane being normal to a surface of the substrate. The metasurface forms a birefringent metasurface.

Feigenbaum, Eyal↗
DOE OSTI2023

Metasurface-assisted 3D beam shaping using array of scatterers

Cascaded metasurfaces can control the phase, amplitude and polarization of an electromagnetic beam, shaping it in three dimensional configuration not achievable with other methods. Each cascaded metasurface has dielectric or metallic scatterers arranged in a period array. The shape of the scatterers determines the three dimensional configuration of the output beam and is determined with iterative calculations through computational simulations.

Kamali, Seyedeh Mahsa↗
DOE OSTI2021

Large aperture and durable glass-engraved optical metasurfaces using nanoparticle etching masks: prospects and future directions

Abstract Metasurfaces (MSs), or surfaces consisting of engineered spatially oriented sub-wavelength elements—also known as meta-atoms—are quickly becoming a burgeoning field of interest due to their seemingly unparalleled control over the propagation of light. This article will discuss the emergence of a MS technology that is based on dewetting thin metal films to form dry etching masks for MS fabrication. The novelty this process presents is the ability to spatially vary mask features—which translates into spatially varying index of the finished surface—in a way that, rather than writing subwavelength elements one-by-one, writes entire areas at once to provide a route to easily scale the process up to meter-sized optics. Glass-engraved MSs have shown to be laser damage resistant, with damage thresholds close to the parent substrate damage thresholds. Furthermore, these surfaces have proven to be mechanically durable and capable of handling normal loads two orders of magnitude higher than that of an average fingerprint pressure. This indicates that accidental handling contact is not detrimental to the MS optical performance. Also discussed are the foreseeable technological challenges, potential solutions for those obstacles, and some currently unexplored directions for future efforts.

47 OTHER INSTRUMENTATION↗
DOE OSTI2024

The Toughness of Interlocking Metasurfaces

Interlocking metasurfaces (ILMs) are arrays of autogenous latching unit cells patterned across a surface. These create structural joints similar to bioinspired suture joints but patterned over a 2D surface rather than a 1D seam. This enables ILMs to be an alternative to conventional joining technologies such as bolts, welds, and adhesives. However, compared to conventional joining methods, relatively little is known of the engineering considerations for designing structural ILMs. Herein, the interfacial toughness of an archetypal ILM is examined for the first time. Under the conditions studied here, the ILM is substantially tougher than the material from which it is made, in this case, exhibiting up to a 50% increase in interfacial crack initiation energy over the solid base material, a photocured 3D‐printed polymer. Through experimental tests using in‐situ digital image correlation along with complementary computational analyses, the mechanism of toughening in the ILM structure and the origins of toughness anisotropy are revealed. The increase in toughness is associated with cross‐cell interactions, that is, load‐sharing across unit cells, which give rise to a finite process zone length with different effective material properties. In this way, ILM toughening is analogous to crack blunting in ductile materials or fiber bridging in composites; yet here, the ILM is composed of a single‐phase base material and so the architected toughening is geometric in nature and hence amenable to future topological optimization.

fracture↗
DOE OSTI2023

All-Glass Metasurfaces for Ultra-Broadband and Large Acceptance Angle Antireflectivity: from Ultraviolet to Mid-Infrared

For many optics technologies, such as display screens, solar cells, laser systems, and eyeglasses, antireflective (AR) coatings are well integrated; these applications frequently benefit from the ability to function as broadband AR. Here, in this work, all-glass metasurfaces are reported on, exhibiting a measured reflectance of 0.18% ± 0.23% per interface, averaged across wavelengths spanning from 350 nm (ultraviolet) to 2350 nm (mid-infrared); to the best of knowledge, this is the first-ever demonstration of an AR layer capable of this. Furthermore, acceptance angles up to 100° (angle of incidence = ±50°) results in % R < 0.6% per interface over the band 350–1300 nm for P-polarization and S-polarization, with wavelength averaged reflectance values 0.04% ± 0.05% and 0.11% ± 0.15%, respectively – another technological first. The process advancements presented here allow for reflectance suppression over a broad range of wavelengths, angles, and polarizations.

36 MATERIALS SCIENCE↗
DOE OSTI2025

MetaHeart: Metasurface enabled biometrics camouflage

Privacy-invading biometrics monitoring is becoming a prominent security threat as modern sensing systems move to higher operating frequencies (mmWave, sub-THz), increasing sensing resolution and accuracy. As such, developing systems that can protect or obfuscate biometrics from adversarial intrusion becomes pivotal to preserving user privacy. In this work, we develop and implement MetaHeart, a real-time biometrics misinformation system based on reflective, programmable metasurfaces and dynamic phase-front manipulation of radar inferences. MetaHeart’s key goal is to prevent the leakage of a legitimate user’s heartbeat biometrics by spoofing fake heartbeat signals at a malicious, radar-equipped, heart rate sensing intruder. Furthermore, we experimentally demonstrate MetaHeart’s ability to fake Alice’s presence when she is not there and to fool Trudy’s inferences even when Alice is present, achieving an overall accuracy above 98%. Finally, we conduct a robustness analysis to determine MetaHeart’s required spatial placement within the intruder’s monitoring area that would allow for effective spoofing.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2024

Active interlocking metasurfaces enabled by shape memory alloys

Interlocking metasurfaces (ILMs) are a newly developed joining technology that relies on arrays of interlocking features that transmit force and constrain motion between adjoining bodies in one or more directions. This study explores harnessing the shape memory effect (SME) in Nickel-Titanium shape memory alloys (NiTi SMAs) in structures fabricated using additive manufacturing (AM) to advance the development of active ILMs by creating unit cells that open or close at specific temperatures. The study encompasses designing and fabricating two distinct interlocking array configurations using near-equiatomic NiTi powder and the laser powder bed fusion (L-PBF) AM technique, following a previously developed AM process optimization framework to manufacture defect-free parts. To guide the design process, finite element analysis (FEA) was employed to predict strain values during engage-disengage cycles. The martensitic transformation characteristics of the ILMs were characterized. Thermomechanical testing revealed that the ILMs demonstrate high locking force once engaged, coupled with complete shape recovery and good cyclic stability. Digital image correlation (DIC) was also employed to validate the FEA predictions during the engage-disengage cycles. The results indicate that NiTi SMA-based ILMs can be designed and fabricated into complex shapes using L-PBF. By leveraging the SME, the functionality of an ILM can be improved upon. The combination of computational modeling, additive manufacturing, and thermomechanical and physical property characterization provides a framework for designing future ILMs out of active materials.

Additive manufacturing↗
DOE OSTI2025

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-MoS 2 metasurfaces (<λ/13 thick). Our measurements, supported by theoretical analysis, reveal a complex interplay and coupling between geometric resonances, optical extinction, and exciton-driven strong nonlinear susceptibility dispersion. We further demonstrate >150-fold enhancement in second harmonic signal at 740 nm mediated 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-MoS 2 nonlinearities at a subwavelength scale, paving the way to ultracompact nonlinear photonic devices.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2025

Bio-inspired interlocking metasurfaces

Interlocking metasurfaces (ILMs) are patterned arrays of mating features that enable the joining of bodies by constraining motion and transmitting force. They offer an alternative to traditional joining solutions such as mechanical fasteners, welds, and adhesives. This study explores the development of bio-inspired ILMs using a problem-driven bioinspired design (BID) framework. We develop a taxonomy of attachment solutions that considers both biological and engineered systems and derive conventional design principles for ILM design. We conceptualize two engineering implementations to demonstrate concept development using the taxonomy and ILM conventional design principle through the BID framework: one for rapidly assembled bridge truss members and another for modular microrobots. These implementations highlight the potential of BID to enhance performance, functionality, and tunability in ILMs.

attachment↗
NASA NTRS2016

Silicon Micromachined Modulated Metasurface Antennas in the Terahertz Range

This paper explores the capabilities of a class of metasurface (MTS), which consists of metalized cylinders on a ground plane, for the realization of modulated MTS antennas at terahertz (THz) frequencies. The proposed structure is particularly appropriate for being micromachined out of a silicon wafer by means of deep reactive ion etching (DRIE). The constraints that DRIE imposes in the design of the MTS unit cell are discussed, along with the advantages of silicon micromachined modulated MTSs with respect to other fabrication approaches in the THz range.

deep-reactive ion etching↗
NASA NTRS2017

Design, Fabrication and Testing of a Modulated Metasurface Antenna at 300 GHz

This paper describes the design and realization of a modulated metasurface (MTS) antenna at 300 GHz. To overcome the hurdles associated with the use of dielectric substrates in the sub-millimeter wave range, we propose an MTS structure which consists of an array of metalized cylinders placed on a ground plane. The metal cylinders are arranged in a square lattice with sub-wavelength unit cell size. This MTS topology has been successfully used to design a spiral MTS antenna. The resulting structure has been micromachined out of a silicon wafer by means of deep reactive ion etching (DRIE). The performance of the antenna has been verified by full-wave simulations, and measurements will be available at the time of the conference.

surface waves↗
NASA NTRS2017

Shared Aperture Metasurface Antennas for Multibeam Patterns

This paper describes various possibilities for designing multibeam antennas using a single metasurface (MTS) aperture. Both single-source and multi-source feeding schemes are considered. For the single-source case, two approaches are investigated: i) division of the aperture in several angular sectors (one per beam) and ii) superposition of the individual modulations required to obtain the beams in the desired directions. A configuration based on a multi-source feeding scheme is also tailored by a superposition of modulation patterns. Numerical results based on the Method of Moments are presented for validation.

leaky waves↗