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Efficient Focusing with Large Numerical Aperture Using a Hybrid Metalens

Physical Review Applied 2020年第4期13卷 044016-044016页

作者： Ming Kang Younes Ra'di Diego Farfan Andrea Alù Department of Electrical and Computer Engineering The University of Texas at Austin Austin Texas 78712 USA Photonics Initiative Advanced Science Research Center City University of New York New York 10031 USA Physics Program Graduate Center City University of New York New York 10016 USA Department of Electrical Engineering City College of The City University of New York New York 10031 USA

Focusing light using electrically thin layers is of paramount importance in several applications, from integrated optics to microwave engineering and sensing. Recently, gradient metasurfaces, which are electrically thin arrays of densely located polarizable particles, have been employed to perform different wave-front transformations, including focusing. In comparison to a bulk lens, these designs provide ultrathin geometries, but they suffer from fundamental limitations on their overall efficiency and achievable numerical aperture. Metagratings offer a solution for efficient beam steering at large angles, but it is challenging to utilize them in the small-angle limit. Here, we introduce a hybrid metalens design, which provides dramatic enhancement in lensing performance compared with that of state-of-the-art metasurfaces, combining metagratings and conventional gradient approaches. Our experimental prototype enables microwave focusing with large efficiency (η=0.479) and near-unity numerical aperture (NA=0.98), yielding a sharp focal point at the diffraction limit in the far field (FWHM=0.332λ). We propose a hybrid metalens design with exceptional performance in terms of efficiency and numerical aperture, opening up opportunities for high-throughput optical lithography, high-density data recording, focal plane arrays, radar, and communication systems.

关键词： Classical optics Integrated optics Metamaterials Optical & microwave phenomena Devices Surfaces

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Thermal Conductivity of BAs under Pressure

arXiv

引用

arXiv 2021年

作者： Hou, Songrui Sun, Bo Tian, Fei Cai, Qingan Xu, Youming Wang, Shanmin Chen, Xi Ren, Zhifeng Li, Chen Wilson, Richard B. Materials Science and Engineering University of California RiversideCA92521 United States Tsinghua Shenzhen International Graduate School Tsinghua University Guangdong Shenzhen518055 China School of Materials Science and Engineering Sun Yat-sen University Guangdong Guangzhou510275 China Department of Physics Texas Center for Superconductivity University of Houston HoustonTX77204 United States Department of Mechanical Engineering University of California RiversideCA92521 United States Department of Electrical and Computer Engineering University of California RiversideCA92521 United States Department of Physics Southern University of Science and Technology Guangdong Shenzhen518055 China

The thermal conductivity of boron arsenide (BAs) is believed to be influenced by phonon scattering selection rules due to its special phonon dispersion. Compression of BAs leads to significant changes in phonon dispersion, which allows for a test of first principles theories for how phonon dispersion affects three- and four-phonon scattering rates. This study reports the thermal conductivity of BAs from 0 to 30 GPa. Thermal conductivity vs. pressure of BAs is measured by time-domain thermoreflectance with a diamond anvil cell. In stark contrast to what is typical for nonmetallic crystals, BAs is observed to have a pressure independent thermal conductivity below 30 GPa. The thermal conductivity of nonmetallic crystals typically increases upon compression. The unusual pressure independence of BAs’s thermal conductivity shows the important relationship between phonon dispersion properties and three- and four-phonon scattering rates. © 2021, CC BY.

关键词： Thermal conductivity

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Thermal conductivity of BAs under pressure

Research Square

引用

Research Square 2021年

作者： Hou, Songrui Sun, Bo Tian, Fei Cai, Qingan Xu, Youming Wang, Shanmin Peng, Wanyue Chen, Xi Ren, Zhifeng Li, Chen Wilson, Richard Materials Science and Engineering University of California RiversideCA92521 United States Tsinghua Shenzhen International Graduate School Tsinghua University Guangdong Shenzhen518055 China School of Materials Science and Engineering Sun Yat-sen University Guangdong Guangzhou510275 China Department of Physics Texas Center for Superconductivity University of Houston HoustonTX77204 United States Department of Mechanical Engineering University of California RiversideCA92521 United States Department of Electrical and Computer Engineering University of California RiversideCA92521 United States Department of Physics Southern University of Science and Technology Guangdong Shenzhen518055 China

Boron arsenide (BAs) is an ultrahigh-thermal-conductivity material with special phonon-phonon scattering behaviors. At ambient pressure, the bunching of acoustic phonon branches in BAs is believed to result in a small phase space for three-phonon scattering. Density functional theory predicts that this acoustic phonon bunching effect is sensitive to pressure and leads to an unusual pressure dependence of thermal conductivity. To explore this physics, we measure the thermal conductivity of BAs from 0 to 25 GPa using time-domain thermoreflectance in a diamond anvil cell. We characterized two BAs samples with ambient thermal conductivities of 350 and 480 W m-1 K-1. Our experiments show that the thermal conductivity of both samples depends weakly on pressure from 0 to 25 GPa. We attribute the weak pressure dependence of the thermal conductivity of BAs to the weak pressure dependence of total phonon-phonon scattering rates. Our experimental results are consistent with DFT predictions that three-phonon scattering rates increase from 0 to 25 GPa, while four-phonon scattering rates decrease. © 2021, CC BY.

关键词： Thermal conductivity

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Persistent flat band splitting and strong selective band renormalization in a kagome magnet thin film

arXiv

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arXiv 2024年

作者： Ren, Zheng Huang, Jianwei Tan, Hengxin Biswas, Ananya Pulkkinen, Aki Zhang, Yichen Xie, Yaofeng Yue, Ziqin Chen, Lei Xie, Fang Allen, Kevin Wu, Han Ren, Qirui Rajapitamahuni, Anil Kundu, Asish K. Vescovo, Elio Kono, Junichiro Morosan, Emilia Dai, Pengcheng Zhu, Jian-Xin Si, Qimiao Minár, Ján Yan, Binghai Yi, Ming Department of Physics and Astronomy Rice University HoustonTX77005 United States Department of Condensed Matter Physics Weizmann Institute of Science Rehovot Israel New Technologies-Research Center University of West Bohemia Plzeň301 00 Czech Republic Applied Physics Graduate Program Smalley-Curl Institute Rice University HoustonTX77005 United States National Synchrotron Light Source II Brookhaven National Lab UptonNY United States Department of Electrical and Computer Engineering Rice University HoustonTX77005 United States Department of Materials Science and NanoEngineering Rice University HoustonTX77005 United States Smalley-Curl Institute Rice University HoustonTX77005 United States Department of Chemistry Rice University HoustonTX77005 United States Theoretical Division Center for Integrated Nanotechnologies Los Alamos National Laboratory Los AlamosNM United States

Magnetic kagome materials provide a fascinating playground for exploring the interplay of magnetism, correlation and topology. Many magnetic kagome systems have been reported including the binary FemXn (X=Sn, Ge;m:n = 3:1, 3:2, 1:1) family and the rare earth RMn6Sn6 (R = rare earth) family, where their kagome flat bands are calculated to be near the Fermi level in the paramagnetic phase. While partially filling a kagome flat band is predicted to give rise to a Stoner-type ferromagnetism, experimental visualization of the magnetic splitting across the ordering temperature has not been reported for any of these systems due to the high ordering temperatures, hence leaving the nature of magnetism in kagome magnets an open question. Here, we probe the electronic structure with angle-resolved photoemission spectroscopy in a kagome magnet thin film FeSn synthesized using molecular beam epitaxy. We identify the exchange-split kagome flat bands, whose splitting persists above the magnetic ordering temperature, indicative of a local moment picture. Such local moments in the presence of the topological flat band are consistent with the compact molecular orbitals predicted in theory. We further observe a large spin-orbital selective band renormalization in the Fe dxy+dx2-y2spin majority channel reminiscent of the orbital selective correlation effects in the iron-based superconductors. Our discovery of the coexistence of local moments with topological flat bands in a kagome system echoes similar findings in magic-angle twisted bilayer graphene, and provides a basis for theoretical effort towards modeling correlation effects in magnetic flat band systems. © 2024, CC BY.

关键词： Iron-based Superconductors

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Routing Optical Spin and Pseudospin with Metasurfaces

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Physical Review Applied 2020年第1期14卷 014029-014029页

作者： Yarden Mazor Andrea Alù Department of Electrical and Computer Engineering The University of Texas at Austin Austin Texas 78712 USA Photonics Initiative Advanced Science Research Center City University of New York New York New York 10031 USA Physics Program Graduate Center City University of New York New York New York 10026 USA

Controlling and guiding optical spins and pseudospins over an interface is of great importance in the emerging fields of spintronics and valleytronics, holding the promise for new degrees of freedom in the quest for efficient information transport. Here we explore the general possibilities offered by metasurfaces to route optical momentum, spin and helicity through surface waves. We show how anisotropy and bianisotropy can be engineered to impart extreme directionality to local spin excitations. While most previous works have focused on out-of-plane spins, in-plane excitations have become particularly important for valleytronic applications relying on two-dimensional materials, and they offer specific challenges addressed here with suitably engineered nonlocality in metasurfaces.

关键词： Metamaterials Optical vortices Photonics Valleytronics Devices Surfaces Transition metal dichalcogenides

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Exploiting Approximations in Supervisory Control with Distinguishers

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IFAC-PapersOnLine 2018年第7期51卷 13-18页

作者： Rosa, Marcelo Teixeira, Marcelo Malik, Robi Graduate Program in Electrical Engineering Federal University of Technology Paraná Pato Branco Brazil Department of Computer Science University of Waikato Hamilton New Zealand

Distinguishers have been used in Supervisory Control Theory (SCT) of Discrete Event Systems, as a way to simplify modeling tasks. Approximations complement this approach with an alternative to also reduce synthesis effort. Despite the advantages, supervisors obtained from approximated DES plants can be suboptimal, so that the modeling structure has to be reconstructed empirically, until the proper supervisor is found. In this paper we show how to construct suitable-approximations that always lead to least restrictive controllable synthesis. A manufacturing system example is provided to illustrate the approach. © 2018

关键词： Discrete event simulation Automation Control engineering Control theory Controllability Manufacture Models Supervisory personnel Controllable synthesis Distinguishers Modeling structures Modeling task Supervisory control Supervisory control theory

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THz Emission from Exchange-Coupled Fe/Ru/Ni Spintronic Emitters

THz Emission from Exchange-Coupled Fe/Ru/Ni Spintronic Emitt...

引用

international Conference on Infrared and Millimeter Waves

作者： R. Adam C. Greb D. E. Bürgler D. Cao S. Heidtfeld F. Wang J. Cheng D. Chakraborty I. Komissarov H. Hardtdegen M. Mikulics M. Büscher C. M. Schneider Roman Sobolewski Research Centre Jülich Peter Grünberg Institute (PGI-6) Jülich Germany Institut für Laser- und Plasmaphysik Heinrich Heine Universität Düsseldorf Düsseldorf Germany College of Physics Center for Marine Observation and Communications Qingdao University Qingdao China Materials Science Graduate Program University of Rochester Rochester New York USA Laboratory for Laser Energetics University of Rochester Rochester New York USA Department of Electrical and Computer Engineering University of Rochester Rochester New York USA Research Centre Jülich Ernst Ruska Centre for Microscopy and Spectroscopy with Electrons Jülich Germany Faculty of Physics University Duisburg-Essen Duisburg Germany Department of Physics University of California Davis Davis California USA

We explored THz emission from $\mathrm{Si}^{2} / \mathrm{SiO}_{2} / / \mathrm{Ta} / \mathrm{Fe} / \mathrm{Ru} /$ $\mathrm{Ni} / \mathrm{Al}_{2} \mathrm{O}_{3}$ spintronic emitters. We tuned magnetization alignment of Fe and Ni layers by varying the interlayer exchange coupling (IEC) strength using a range of Ru layer thickness t. Depending on IEC strength, magnetization hysteresis shows either ferromagnetic $(t=1.1 \mathrm{~nm}, 1.5 \mathrm{~nm})$, antiferromagnetic $(t=1.3 \mathrm{~nm})$ or canted $(t=1.7 \mathrm{~nm}, 1.9 \mathrm{~nm})$ relative alignment. Competition between IEC and an external magnetic field results in a dramatic difference in THz emission from the ferromagnetically (FM) and anti-ferromagnetically (AFM) coupled structures. The resulting THz emission from IEC structures is a result of an interference of THz transiens generated by the individual $\mathrm{Fe} / \mathrm{Ru}$ and $\mathrm{Ru} / \mathrm{Ni}$ emitters.

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Analysis of Negative Capacitance MOSFETs Characteristic with Spacer

Analysis of Negative Capacitance MOSFETs Characteristic with...

引用

international Symposium on VLSI Technology, Systems and Applications

作者： Yu-Chun Lee Sekhar Reddy Kola Chieh-Yang Chen Min-Hui Chuang Yiming Li Parallel and Scientific Computing Laboratory Institute of Biomedical Engineering EECS International Graduate Program Institute of Communications Engineering Department of Electrical and Computer Engineering National Chiao Tung University Hsinchu Taiwan Center for mmWave Smart Radar System and Technologies National Chiao Tung University 1001 Ta-Hsueh Rd Hsinchu Taiwan

ISBN: (数字)9781728142326

ISBN: (纸本)9781728142333

In this work, our study comprises of design and investigation on negative capacitance (NC), metal-oxide-semiconductor (MOS) field effects transistors (MOSFETs) with spacer and source/drain (S/D) overlap engineering. The scope of the work is to boost the performance and high-energy efficiency of the studied NC-MOSFETs by using the ferro electric material (FE). The NC-MOSFETs with the spacer technology can achieve the admirable I on /I off ratio and subthreshold swing (SS), compared with planar MOSFETs. It makes device scaling possible by eliminating the short channel effect (SCE). We further estimated the effect of FE thickness and spacer, which are another critical parameter of obtaining better electrical characteristics and reducing SS.

关键词： Capacitance Iron Semiconductor device modeling MOSFET Integrated circuit modeling Mathematical model Ferroelectric materials

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Corrections to "iPhantom: A Framework for Automated Creation of Individualized Computational Phantoms and its Application to CT Organ Dosimetry"

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IEEE journal of biomedical and health informatics 2022年第1期26卷 478页

作者： Wanyi Fu Shobhit Sharma Ehsan Abadi Alexandros-Stavros Iliopoulos Qi Wang Joseph Y Lo Xiaobai Sun William P Segars Ehsan Samei Department of Electrical and Computer Engineering and Carl E. Ravin Advanced Imaging Laboratories Duke University Durham NC USA Department of Physics and Carl E. Ravin Advanced Imaging Laboratories Duke University Durham NC USA Department of Computer Science Duke University Durham NC USA Computer Science and Artificial Intelligence Laboratory Massachusetts Institute of Technology Cambridge MA USA Department of Radiology the Fourth Clinical Hospital of Hebei Medical University Heibei China Departments of Electrical and Computer Engineering Biomedical Engineering Medical Physics Graduate Program and Carl E. Ravin Advanced Imaging Laboratories Duke University Durham NC USA Medical Physics Graduate Program and Radiology and the Carl E. Ravin Advanced Imaging Laboratories Departments of Biomedical Engineering Duke University Durham NC USA Carl E. Ravin Advanced Imaging Laboratories Medical Physics Graduate Program Department of Radiology Electrical and Computer Engineering Biomedical Engineering and Physics Duke University Durham NC USA

In [1], the dose estimation accuracy using the alternative baseline method under modulated tube current was not correctly calculated due to an unintentional simulation error.

关键词： Phantoms Image segmentation Computed tomography Image registration

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Extreme electrodynamics in time-varying media

arXiv

引用

arXiv 2025年

作者： Scalora, M. Vincenti, M.A. de Ceglia, D. Akozbek, N. Ferrera, M. Rizza, C. Alù, A. Litchinitser, N. Cojocaru, C. Trull, J. FCDD-AMT-MGR DEVCOM AvMC C. M. Bowden Research Center Redstone ArsenalAL35898-5000 United States Department of Information Engineering University of Brescia Brescia25123 Italy US Army Space & Missile Defense Command Tech Center Redstone ArsenalAL35898 United States Institute of Photonics and Quantum Sciences Heriot-Watt University SUPA EdinburghEH14 4AS United Kingdom Department of Physical and Chemical Sciences University of L’Aquila L’AquilaI-67100 Italy Photonics Initiative Advanced Science Research Center City University of New York New YorkNY10031 United States Physics Program Graduate Center City University of New York New YorkNY10016 United States Department of Electrical and Computer Engineering Duke University DurhamNC27708 United States Department of Physics Universitat Politècnica de Catalunya Barcelona Terrassa08222 Spain

Abrupt time variations of the properties of optical materials have been at the center of intense research efforts in recent years, with the prospect of enabling extreme wave transformations and of leveraging time as a degree of freedom for wave control. While the most viable approach to yield ultrafast variations of the optical material response is through optical pumping of nonlinear media, the complex dynamics in these systems are not yet fully understood. Here, as a relevant case study, we rigorously investigate the pump-probe dynamics in a 310nm-thick transparent conductive oxide etalon, using a weak 40 femtosecond probe and a pump that displays peak power densities in the TW/cm2 range with a duration of a few femtoseconds. We examine the pump-probe interaction using a hydrodynamic-Maxwell approach that accounts for diffraction, self-focusing and -defocusing, self- and cross-phase modulation, probe gain, and linear and nonlinear material dispersion expanded in the perturbative regime up to 9th order for both pump and probe. By allowing the intricacies of the pump-probe interaction to proceed in time, we can also define an effective spatio-temporal permittivity for a more direct evaluation of the material ultra-broadband optical behavior. The reported results challenge the conventional modeling of this kind of problem, which has so far overlooked pump dynamics, simplistically assigning a local time-dependent refractive index to the probe that may be designed to fit the experimental data, but has no physical connection to the complex pump-probe interaction. Our approach unveils new dynamics, pointing towards the possibility to achieve extreme pulse compression into the attosecond range and nonlinear diffraction over deeply subwavelength propagation distances, thus opening a possible new path towards novel and cost-effective tools for integrated photonics and attosecond science. © 2025, CC BY-NC-ND.

关键词： Probes

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