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Performance Limits of Graphene Hot Electron Emission Photoemitters

Physical Review Applied 2020年第2期13卷 024060-024060页

作者： Ragib Ahsan Mashnoon Alam Sakib Hyun Uk Chae Rehan Kapadia Department of Electrical and Computer Engineering University of Southern California Los Angeles 90089 CA United States

Hot electron emission from waveguide-integrated graphene has been recently shown to occur at optical power densities multiple orders of magnitude lower than that of metal tips excited by sub-work-function photons. However, the experimentally observed electron emission currents are small, which limits the practical uses of such a mechanism. Here, we explore the performance limits of hot electron emission in graphene through experimentally calibrated simulations. Two regimes of nonequilibrium emission in graphene are identified, (i) single particle hot electron emission, where an electron is excited by a photon and emitted before losing significant energy through scattering; and (ii) ensemble hot electron emission, where the photon source causes nonequilibrium heating of the electron population beyond the electron lattice temperature. It is shown that, through appropriate selection of photon energy, optical power density, and applied electric field, hot electron emission can be used to create ultrahigh current electron emitters with ultrafast temporal responses in both the single particle and ensemble heating regimes. These results suggest that, through appropriate design, hot electron emitters may overcome the limitations of thermionic and field emitters.

关键词： Electron beams & optics Field emission Photoemission Thermionic emission Graphene Waveguides Boltzmann theory Monte Carlo methods

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X-ray microscopy instrumentation developments at NSLS-ii: recent progress and future directions 4

X-ray microscopy instrumentation developments at NSLS-II: re...

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Conference on X-Ray Nanoimaging - Instruments and Methods IV held at SPIE optical engineering + Applications Conference

作者： Nazaretski, E. Xu, W. Yan, H. Huang, X. Xu, Wei Bouet, N. Zhou, J. Coburn, D. S. Lee, W. -K. Ge, M. Huang, L. Idir, M. Chu, Y. S. Brookhaven Natl Lab Upton NY 11973 USA

ISBN: (数字)9781510629189

ISBN: (纸本)9781510629189

X-ray microscopy is a mature characterization tool routinely used to answer various questions of science, technology and engineering. The high penetration power of X-rays allows to utilize different characterization methods and reveal elemental composition, crystalline phases, strain distribution, oxidation states etc. in macroscopic and microscopic samples. To obtain comprehensive chemical and structural information at the nanometer scale an X-ray microscope must be equipped with adequate capabilities and allow acquisition of multiple datasets simultaneously. Full-field or scanning X-ray microscopes usually serve this purpose and complement each other. In the recent years, a number of X-ray microscopes have been designed, constructed and commissioned at NSLS-ii. In this work we provide an overview of the microscopy instrumentation developments at NSLS-ii. It includes the multilayer Laue Lens based nanoprobe optimized for 10 nm spatial resolution imaging, it's current status and future upgrades;the zone plate based full-field imaging system capable of nano-tomography measurements in less than 1 minute;a laser scanning system optimized for ptychography measurements along with algorithms development, and a new Kirkpatrick-Baez based scanning microscope designed for sub-100 nm spatial resolution experiments.

关键词： X-ray focusing MLLs X-ray microscopy Nano-positioning

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Integrated multi-objective optimisation of the support structure of heliostats in concentrated solar power plants using a genetic algorithm

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IOP Conference Series: Materials Science and engineering 2022年第1期1214卷

作者： L Lomazzi F Cadini M Giglio C Cancro G Ciniglio G Graditi A Pontecorvo Politecnico di Milano Department of Mechanical Engineering Via La Masa n.1 Milan Italy Italian National Agency for New Technologies Energy and Sustainable Economic Development ENEA – Research Center Piazza E. Fermi 1 80055 Portici (NA) Italy

The optimisation of the support structure of heliostats in concentrating solar power plants is a fundamental task aimed at attempting to reduce the high levelised cost of energy (LCOE) of current configurations. In this work, an integrated multi-objective optimisation framework is presented, which relies on the combination of a lean and fast structural model with a genetic algorithm to simultaneously minimise both the overall mass of the support structure and the mean angle of rotation of the mirror surface, which directly affects the optical efficiency of the component. A particular feature of the proposed framework is that it represents an integrated solution, i.e., it allows to simultaneously optimise the main components of the heliostat support structure, i.e., the pedestal, the truss and the back support structure, assuming they are off-the-shelf components easily available on the market. The optimisation problem is set up selecting as design variables (i) the number of elements in the back support structure and (ii) the relevant characteristics of all the components considered, i.e., section shape and dimensions, according to the components commercial datasheets. At each iteration of the optimisation process, the structural model is fed with the current design variables values and, according to some computed aerodynamic loads, it allows evaluating the displacement and rotation of the points of interest within the mirror surface. An aerodynamic model present in the literature based on experimental wind tunnel tests is used to estimate the wind forces acting on the heliostat as a function both of the mirror inclination angle with respect to the ground and of the wind direction with respect to the mirror orientation. In this work, the proposed methodology is demonstrated on a realistic case study and the results commented in detail, highlighting possible future developments and the limitations of the framework.

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optical designs of the objectives for special studies in polarizing microscope 19

Optical designs of the objectives for special studies in pol...

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19th Conference on current developments in Lens design and optical engineering

作者： Frolov, Dmitry N. Vinogradova, Olga A. Frolov, Alexey D. Tabachkov, Alexey G. Project Labor Microscopes Zapovednaya St 51A St Petersburg 194356 Russia

Presents the results of the optical design of lens objectives for polarization light microscopes, including to ensure that the special techniques. Sometimes such methods require the use of objectives similar magnifica... 详细信息

ISBN: (数字)9781510620629

ISBN: (纸本)9781510620629

关键词： Microscopy Lens system design optical design and fabrication Objectives for microscopes Lens objectives system design Objectives for polarizing microscopes Polarizing microscopy

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Modular plug-in extension enabling cross-dispersed spectroscopy for Large Binocular Telescope 2

Modular plug-in extension enabling cross-dispersed spectrosc...

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Symposium on Astronomical Optics - design, Manufacture, and Test of Space and Ground Systems ii held at SPIE optical engineering + Applications Conference

作者： Kang, Hyukmo Thompson, David Conrad, Al Vogel, Conrad Lamdan, Ariel Kim, Dae Wook Univ Arizona James C Wyant Coll Opt Sci 1630 E Univ Blvd Tucson AZ 85721 USA Large Binocular Telescope Observ 933 N Cherry Ave Tucson AZ 85721 USA Univ Arizona Dept Astron 933 N Cherry Ave Tucson AZ 85721 USA

ISBN: (数字)9781510629264

ISBN: (纸本)9781510629257;9781510629264

The LUCI (LBT Utility Camera in the Infrared) instruments are a pair of near infrared (NIR) imagers and spectrographs for the Large Binocular Telescope (LBT) that include a set of cryogenic exchangeable focal plane masks. Although LUCI covers the NIR zJHK bands at different resolutions with existing gratings, it is not currently possible to get zJHK in a single exposure with a single LUCI which is required for some planetary science programs. To produce a simultaneous zJHK spectrum with a single LUCI, we designed a system consisting of small and simple optical elements to fit within the limited space in the focal plane mask frame to cross-disperse fixed short slits. This system, called MOBIUS (Mask-Oriented Breadboard Implementation for Unscrambling Spectra), consists of a double-folding mirror, a collimating spherical mirror with 180 mm radius of curvature, and a dispersing prism with the rear surface mirror-coated. MOBIUS disperses the input slit perpendicular to the dispersion direction of the gratings in LUCI. The resulting order separation is at least similar to 2.7 arcsecond, allowing a slit length of up to similar to 2.3 arcsec without mixing orders at the LUCI image plane. Since MOBIUS would be introduced into the existing light path via the exchangeable slit mask mechanism, no modification to the current LUCI instrument is needed. Eventually, binocular observations combining one of the Multi-Object Double Spectrographs (MODS) with LUCI+MOBIUS at the LBT will provide simultaneous coverage from 0.3 to 2.4 mu m for studies of asteroids and other faint solar system bodies.

关键词： LBT LUCI Spectrograph Cross dispersion Instrument design

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optical design of CCF PlanApo microobjectives 50 mm observation and super long working distance 19

Optical design of CCF PlanApo microobjectives 50 mm observat...

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19th Conference on current developments in Lens design and optical engineering

作者： Frolov, Dmitry N. Vinogradova, Olga A. Frolov, Alexey D. Wen, Liyun Jing, Fanhua Project Labor Microscopes Zapovednaya St 51A St Petersburg 194356 Russia Kozo Opt Ltd 19E18 Zhenghong St Nanjing Jiangsu Peoples R China

The main difference is a significant expansion of the linear field, which reaches 50 mm in the image plane. However, in this case, a planapochromatic correction must be achieved for the usual visible spectral range. S... 详细信息

ISBN: (数字)9781510620629

ISBN: (纸本)9781510620629

关键词： Lens system design optical design and fabrication Microscopy Objectives for microscopes

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optical design of LED Marine Beacons 19

Optical Design of LED Marine Beacons

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19th Conference on current developments in Lens design and optical engineering

作者： Lin, Shih-Kang Jen, Yung-Chang Lee, Xuan-Hao Yu, Yeh-Wei Yang, Tsung-Hsun Sun, Ching-Cherng Natl Cent Univ Dept Opt & Photon Chungli 32001 Taiwan Natl Cent Univ Opt Sci Ctr Taoyuan 32001 Taiwan

ISBN: (数字)9781510620629

ISBN: (纸本)9781510620629

Two optical designs for marine beacon based on Direct In-line Package (DIP) LED is proposed and demonstrated. The luminous intensity of the marine beacon using DIP LED can achieve to the IALA recommendation's requirement of 5 nautical miles. The measurement of color coordinates can also fit the IALA recommendation's requirement. By the surface-structured TIR lens, we successfully keep the divergence angle to 68 degrees in the horizontal direction and converge to 8 degrees in the vertical direction.

关键词： DIP LED optical design marine beacons IALA

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design and Prototyping of a Freeform Light-Guide for Automotive Lighting 19

Design and Prototyping of a Freeform Light-Guide for Automot...

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19th Conference on current developments in Lens design and optical engineering

作者： Brand, Audrey C. Alisafaee, Hossein Rose Hulman Inst Technol Dept Phys & Opt Engn 5500 Wabash Ave Terre Haute IN 47803 USA

ISBN: (数字)9781510620629

ISBN: (纸本)9781510620629

We have designed a light-guide for lighting applications, including automotive headlamps. The light-guide is designed based on a free-form slab. Our intention has been to optimize the design for creating legal patterns. One of our objectives has been to investigate how the changes in the shape of the freeform light-guide affects the light pattern, and how the light source geometry affects the design. For prototyping purpose, we use a particular polymer that exhibits optical performance close to acrylic (PMMA).

关键词： Automotive Lighting Lighting Light-guide optical design Illumination

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Coronary artery segmentation from intravascular optical coherence tomography using deep capsules

arXiv

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arXiv 2020年

作者： Balaji, Arjun Kelsey, Lachlan J. Majeed, Kamran Schultz, Carl J. Doyle, Barry J. Vascular Engineering Laboratory Harry Perkins Institute of Medical Research QEII Medical Centre Nedlands and Centre for Medical Research The University of Western Australia Perth Australia School of Engineering The University of Western Australia Perth Australia Department of Cardiology Royal Perth Hospital Perth Australia School of Medicine The University of Western Australia Perth Australia University of Ottawa Heart Institute OttawaON Canada Australian Research Council Centre for Personalised Therapeutics Technologies Australia British Heart Foundation Centre for Cardiovascular Science The University of Edinburgh United Kingdom

The segmentation and analysis of coronary arteries from intravascular optical coherence tomography (IVOCT) is an important aspect of diagnosing and managing coronary artery disease. current image processing methods are hindered by the time needed to generate expert-labelled datasets and the potential for bias during the analysis. Therefore, automated, robust, unbiased and timely geometry extraction from IVOCT, using image processing, would be beneficial to clinicians. With clinical application in mind, we aim to develop a model with a small memory footprint that is fast at inference time without sacrificing segmentation quality. Using a large IVOCT dataset of 12,011 expert-labelled images from 22 patients, we construct a new deep learning method based on capsules which automatically produces lumen segmentations. Our dataset contains images with both blood and light artefacts (22.8%), as well as metallic (23.1%) and bioresorbable stents (2.5%). We split the dataset into a training (70%), validation (20%) and test (10%) set and rigorously investigate design variations with respect to upsampling regimes and input selection. We show that our developments lead to a model, DeepCap, that is on par with state-of-the-art machine learning methods in terms of segmentation quality and robustness, while using as little as 12% of the parameters. This enables DeepCap to have per image inference times up to 70% faster on GPU and up to 95% faster on CPU compared to other state-of-the-art models. DeepCap is a robust automated segmentation tool that can aid clinicians to extract unbiased geometrical data from IVOCT. © 2020, CC BY.

关键词： optical tomography

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design and analysis of the mirror system with off-axis field-of-view 19

Design and analysis of the mirror system with off-axis field...

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19th Conference on current developments in Lens design and optical engineering

作者： Romanova, Galina E. Rodionova (Butylkina), Kseniia D. ITMO Univ 49 Kronverkskiy Pr St Petersburg 197101 Russia

ISBN: (数字)9781510620629

ISBN: (纸本)9781510620629

Nowadays, the development of the space apparatus with high optical characteristics still stays the important task. The simplest systems which can provide the required characteristics for remote monitoring from the space are the three-mirror systems. It can be shown that in many cases, classical three-mirror systems have critical value of obscuration that leads to decreasing of resolution. Using off-axis field of view in the systems provides the way to avoid the obscuration influence. We present a technique for designing the three-mirror telescope objectives based on the systems with axial symmetry with an off-axis field of view.

关键词： mirror telescopes off-axis field of view optical design

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