scholarly journals Quasi-Continuous Metasurface Beam Splitters Enabled by Vector Iterative Fourier Transform Algorithm

Materials ◽  
2021 ◽  
Vol 14 (4) ◽  
pp. 1022 ◽  
Author(s):  
Jinzhe Li ◽  
Fei Zhang ◽  
Mingbo Pu ◽  
Yinghui Guo ◽  
Xiong Li ◽  
...  
Keyword(s):  
Fourier Transform ◽  
Computational Cost ◽  
Three Dimensional ◽  
Diffraction Theory ◽  
Optical Systems ◽  
Subwavelength Structures ◽  
Beam Splitters ◽  
Scalar Diffraction ◽  
Target Energy ◽  
Diffraction Patterns

Quasi-continuous metasurfaces are widely used in various optical systems and their subwavelength structures invalidate traditional design methods based on scalar diffraction theory. Here, a novel vector iterative Fourier transform algorithm (IFTA) is proposed to realize the fast design of quasi-continuous metasurface beam splitters with subwavelength structures. Compared with traditional optimization algorithms that either require extensive numerical simulations or lack accuracy, this method has the advantages of accuracy and low computational cost. As proof-of-concept demonstrations, several beam splitters with custom-tailored diffraction patterns and a 7 × 7 beam splitter are numerically demonstrated, among which the maximal diffraction angle reaches 70° and the best uniformity error reaches 0.0195, showing good consistency with the target energy distribution and these results suggest that the proposed vector IFTA may find wide applications in three-dimensional imaging, lidar techniques, machine vision, and so forth.

DIFFRACTION OF 3.2 CM. ELECTROMAGNETIC WAVES BY CYLINDRICAL OBJECTS

1954 ◽  
Vol 32 (6) ◽  
pp. 372-380 ◽  
Author(s):  
A. B. McLay ◽  
S. T. Wiles
Keyword(s):  
Electromagnetic Waves ◽  
Incident Beam ◽  
Diffraction Theory ◽  
Central Peak ◽  
Beam Direction ◽  
Cylinder Axis ◽  
Scalar Diffraction ◽  
Conducting Cylinder ◽  
Scalar Diffraction Theory ◽  
Diffraction Patterns

Diffraction patterns of a brass tube and a hard rubber rod, each a cylinder of 1 in. diameter, in a nearly plane beam of square-wave modulated 3 cm. waves with electric vector parallel to the cylinder axis, have been measured in several planes transverse to the incident beam direction. Experimental results for the conducting cylinder agree closely with calculations based on scalar diffraction theory. Patterns of the dielectric rod show a pronounced central peak immediately behind the rod and other intensity effects differing from the conducting cylinder patterns, particularly in the vicinity of the shadow.

Nouvelles conditions aux limites exactes pour les champs électromagnétiques à la surface des matériaux absorbants

1983 ◽  
Vol 61 (2) ◽  
pp. 332-347 ◽  
Author(s):  
Pierre Langlois ◽  
Alberic Boivin
Keyword(s):  
Boundary Conditions ◽  
Diffraction Theory ◽  
Visible Range ◽  
Scalar Diffraction ◽  
Edge Diffraction ◽  
Conditions Aux Limites ◽  
Exact Boundary ◽  
Good Conductor ◽  
Diffraction Patterns ◽  
Materials Used

Recent experiments using laser light by Langlois et al. have shown for the first time that actual diffraction patterns from edges do depend on the material and ridge shape of the scatterer, as well as on the polarization of the incident wave. These results have brought out the inadequacy of the scalar diffraction theory for diffraction angles larger than about 1°. Farther out one must use exact electromagnetic theory, with the attendant requirement that exact boundary conditions be known for the fields on the surface of the scattering object. These boundary conditions are well known for perfect conductors (Neumann's or Dirichlet's conditions) or even for good conductors (Leontovich's conditions). However, in the visible range one finds that copper is not a good conductor. Therefore, we develop in the present paper new exact boundary conditions, which generalize those of Leontovieh. In actual fact our new boundary conditions have enabled us to perform edge diffraction calculations for a considerably larger range of complex refraction indices covering the materials used. More generally one may claim that our boundary conditions do apply for all usual materials (copper, aluminium, ebonite … ), in as much as they are absorbing and the local ridge curvature of the scattering objects is far larger than the wavelength.

Scalar diffraction in terms of coherence

1959 ◽  
Vol 249 (1259) ◽  
pp. 574-588 ◽  
Keyword(s):  
Transfer Function ◽  
Fourier Transforms ◽  
Monochromatic Light ◽  
Diffraction Theory ◽  
Optical Systems ◽  
Coherence Transfer ◽  
Transfer Factors ◽  
Scalar Diffraction ◽  
Partially Coherent ◽  
Special Cases

In scalar diffraction theory, an optical instrument can be treated as a linear system for the two limiting cases of coherent and incoherent illumination of the object, these treatments being in terms of complex amplitude and intensity, respectively. But when the illumination of the object is partially coherent, the system is no longer linear in either of these quantities and a two-stage treatment involving both quantities has been customary. Wolf has indicated the advantages of formulating diffraction theory in terms of an observable correlation function, here called the ‘coherence’, rather than in quantities such as amplitude which are not observable at optical frequencies. A Fourier theory of diffraction is developed here based on the coherence between radiation at pairs of points. As in general the coherence across a plane is a function of four spatial co-ordinates, the Fourier transforms used are in four dimensions for monochromatic light and in five for light of a finite spectral bandwidth. This diffraction theory is linear for all optical systems with illumination of any degree of coherence and leads to the concept of a ‘coherence transfer function’ to describe the performance of the instrument. In special cases, this reduces to the well-known ‘contrast transfer function' for incoherent illumination and to the transfer factors used in Hopkins’s treatment of partially coherent illumination. The theory also gives the transfer properties and the compensations required for two-beam interferometers and shows how the wave-shearing interferometer serves as an instrument for measuring coherence.

scholarly journals DF-Fit: A Robust Algorithm for Detection of Crystallographic Information in Atom Probe Tomography Data

2019 ◽  
Vol 25 (2) ◽  
pp. 331-337
Author(s):  
Daniel Haley ◽  
Paul A. J. Bagot ◽  
Michael P. Moody
Keyword(s):  
Fourier Transform ◽  
Spatial Data ◽  
Atom Probe Tomography ◽  
Computational Cost ◽  
Three Dimensional ◽  
Atom Probe ◽  
Real Space ◽  
Distribution Functions ◽  
Quality Data ◽  
Error Metric

AbstractWe report on a new algorithm for the detection of crystallographic information in three-dimensional, as retained in atom probe tomography (APT), with improved robustness and signal detection performance. The algorithm is underpinned by one-dimensional distribution functions (DFs), as per existing algorithms, but eliminates an unnecessary parameter as compared to current methods.By examining traditional DFs in an automated fashion in real space, rather than using Fourier transform approaches, we utilize an error metric based upon the expected value for a spatially random distribution for detecting crystallography. We show cases where the metric is able to successfully obtain orientation information, and show that it can function with high levels of additive and displacive background noise. We additionally compare this metric to Fourier transform methods, showing fewer artifacts when examining simulated datasets. An extension of the approach is used to aid the automatic detection of high-quality data regions within an entire dataset, albeit with a large increase in computational cost.This extension is demonstrated on acquired aluminum and tungsten APT datasets, and shown to be able to discern regions of the data which have relatively improved spatial data quality. Finally, this program has been made available for use in other laboratories undertaking their own analyses.

Cryomicroscopy of crotoxin complex crystals at 400 KV

1989 ◽  
Vol 47 ◽  
pp. 826-827
Author(s):  
Jaap Brink ◽  
Wah Chiu
Keyword(s):  
Signal To Noise Ratio ◽  
3D Structure ◽  
Three Dimensional ◽  
Carbon Films ◽  
Depth Of Field ◽  
Basic Subunit ◽  
Ewald Sphere ◽  
Diffraction Patterns ◽  
Complex Crystals ◽  
Acidic Subunit

The crotoxin complex is a potent neurotoxin composed of a basic subunit (Mr = 12,000) and an acidic subunit (M = 10,000). The basic subunit possesses phospholipase activity whereas the acidic subunit shows no enzymatic activity at all. The complex's toxocity is expressed both pre- and post-synaptically. The crotoxin complex forms thin crystals suitable for electron crystallography. The crystals diffract up to 0.16 nm in the microscope, whereas images show reflections out to 0.39 nm2. Ultimate goal in this study is to obtain a three-dimensional (3D-) structure map of the protein around 0.3 nm resolution. Use of 100 keV electrons in this is limited; the unit cell's height c of 25.6 nm causes problems associated with multiple scattering, radiation damage, limited depth of field and a more pronounced Ewald sphere curvature. In general, they lead to projections of the unit cell, which at the desired resolution, cannot be interpreted following the weak-phase approximation. Circumventing this problem is possible through the use of 400 keV electrons. Although the overall contrast is lowered due to a smaller scattering cross-section, the signal-to-noise ratio of especially higher order reflections will improve due to a smaller contribution of inelastic scattering. We report here our preliminary results demonstrating the feasability of the data collection procedure at 400 kV.Crystals of crotoxin complex were prepared on carbon-covered holey-carbon films, quench frozen in liquid ethane, inserted into a Gatan 626 holder, transferred into a JEOL 4000EX electron microscope equipped with a pair of anticontaminators operating at −184°C and examined under low-dose conditions. Selected area electron diffraction patterns (EDP's) and images of the crystals were recorded at 400 kV and −167°C with dose levels of 5 and 9.5 electrons/Å, respectively.

Atomic Resolution in Crystal Aperture Stem

1990 ◽  
Vol 48 (1) ◽  
pp. 236-237
Author(s):  
J T Fourie
Keyword(s):  
Optical System ◽  
Spherical Aberration ◽  
Three Dimensional ◽  
Transmission Function ◽  
Optical Systems ◽  
Bragg Angle ◽  
Electron Optical System ◽  
Intimate Contact ◽  
Diffraction Effects ◽  
Design Aspect

The attempts at improvement of electron optical systems to date, have largely been directed towards the design aspect of magnetic lenses and towards the establishment of ideal lens combinations. In the present work the emphasis has been placed on the utilization of a unique three-dimensional crystal objective aperture within a standard electron optical system with the aim to reduce the spherical aberration without introducing diffraction effects. A brief summary of this work together with a description of results obtained recently, will be given.The concept of utilizing a crystal as aperture in an electron optical system was introduced by Fourie who employed a {111} crystal foil as a collector aperture, by mounting the sample directly on top of the foil and in intimate contact with the foil. In the present work the sample was mounted on the bottom of the foil so that the crystal would function as an objective or probe forming aperture. The transmission function of such a crystal aperture depends on the thickness, t, and the orientation of the foil. The expression for calculating the transmission function was derived by Hashimoto, Howie and Whelan on the basis of the electron equivalent of the Borrmann anomalous absorption effect in crystals. In Fig. 1 the functions for a g220 diffraction vector and t = 0.53 and 1.0 μm are shown. Here n= Θ‒ΘB, where Θ is the angle between the incident ray and the (hkl) planes, and ΘB is the Bragg angle.

Handheld Laser Scanner Research

2019 ◽  
Vol 952 (10) ◽  
pp. 47-54
Author(s):  
A.V. Komissarov ◽  
A.V. Remizov ◽  
M.M. Shlyakhova ◽  
K.K. Yambaev
Keyword(s):  
Point Cloud ◽  
Three Dimensional ◽  
Laser Scanner ◽  
Test Site ◽  
Optical Systems ◽  
Advantages And Disadvantages ◽  
Site Survey ◽  
Laser Scanners ◽  
Three Dimensional Models ◽  
The Stability

The authors consider hand-held laser scanners, as a new photogrammetric tool for obtaining three-dimensional models of objects. The principle of their work and the newest optical systems based on various sensors measuring the depth of space are described in detail. The method of simultaneous navigation and mapping (SLAM) used for combining single scans into point cloud is outlined. The formulated tasks and methods for performing studies of the DotProduct (USA) hand-held laser scanner DPI?8X based on a test site survey are presented. The accuracy requirements for determining the coordinates of polygon points are given. The essence of the performed experimental research of the DPI?8X scanner is described, including scanning of a test object at various scanner distances, shooting a test polygon from various scanner positions and building point cloud, repeatedly shooting the same area of the polygon to check the stability of the scanner. The data on the assessment of accuracy and analysis of research results are given. Fields of applying hand-held laser scanners, their advantages and disadvantages are identified.

scholarly journals Hyperspectral Three-Dimensional Fluorescence Imaging Using Snapshot Optical Tomography

Sensors ◽  
2021 ◽  
Vol 21 (11) ◽  
pp. 3652
Author(s):  
Cory Juntunen ◽  
Isabel M. Woller ◽  
Yongjin Sung
Keyword(s):  
Fourier Transform ◽  
3D Imaging ◽  
Optical Tomography ◽  
Three Dimensional ◽  
High Spectral Resolution ◽  
Functional Information ◽  
Fluorescent Beads ◽  
Different Depths ◽  
Projection Images ◽  
Imaging Performance

Hyperspectral three-dimensional (3D) imaging can provide both 3D structural and functional information of a specimen. The imaging throughput is typically very low due to the requirement of scanning mechanisms for different depths and wavelengths. Here we demonstrate hyperspectral 3D imaging using Snapshot projection optical tomography (SPOT) and Fourier-transform spectroscopy (FTS). SPOT allows us to instantaneously acquire the projection images corresponding to different viewing angles, while FTS allows us to perform hyperspectral imaging at high spectral resolution. Using fluorescent beads and sunflower pollens, we demonstrate the imaging performance of the developed system.

scholarly journals “Perfect” Terahertz Vortex Beams Formed Using Diffractive Axicons and Prospects for Excitation of Vortex Surface Plasmon Polaritons

2021 ◽  
Vol 11 (2) ◽  
pp. 717
Author(s):  
Boris Knyazev ◽  
Valery Cherkassky ◽  
Oleg Kameshkov
Keyword(s):  
Surface Plasmon ◽  
Surface Plasmon Polaritons ◽  
Bessel Beam ◽  
Diffraction Theory ◽  
Terahertz Range ◽  
High Resistivity ◽  
Visible Range ◽  
Optical Elements ◽  
Scalar Diffraction ◽  
Plasmon Polaritons

Transformation of a Bessel beam by a lens results in the formation of a “perfect” vortex beam (PVB) in the focal plane of the lens. The PVB has a single-ring cross-section and carries an orbital angular momentum (OAM) equal to the OAM of the “parent” beam. PVBs have numerous applications based on the assumption of their ideal ring-type structure. For instance, we proposed using terahertz PVBs to excite vortex surface plasmon polaritons propagating along cylindrical conductors and the creation of plasmon multiplex communication lines in the future (Comput. Opt. 2019, 43, 992). Recently, we demonstrated the formation of PVBs in the terahertz range using a Bessel beam produced using a spiral binary silicon axicon (Phys. Rev. A 2017, 96, 023846). It was shown that, in that case, the PVB was not annular, but was split into nested spiral segments, which was obviously a consequence of the method of Bessel beam generation. The search for methods of producing perfect beams with characteristics approaching theoretically possible ones is a topical task. Since for the terahertz range, there are no devices like spatial modulators of light in the visible range, the main method for controlling the mode composition of beams is the use of diffractive optical elements. In this work, we investigated the characteristics of perfect beams, the parent beams being quasi-Bessel beams created by three types of diffractive phase axicons made of high-resistivity silicon: binary, kinoform, and “holographic”. The amplitude-phase distributions of the field in real perfect beams were calculated numerically in the approximation of the scalar diffraction theory. An analytical expression was obtained for the case of the binary axicon. It was shown that a distribution closest to an ideal vortex was obtained using a holographic axicon. The resulting distributions were compared with experimental and theoretical distributions of the evanescent field of a plasmon near the gold–zinc sulfide–air surface at different thicknesses of the dielectric layer, and recommendations for experiments were given.

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