scholarly journals Broadband Achromatic Metasurfaces for Longwave Infrared Applications

Nanomaterials ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 2760
Author(s):  
Naitao Song ◽  
Nianxi Xu ◽  
Dongzhi Shan ◽  
Yuanhang Zhao ◽  
Jinsong Gao ◽  
...  
Keyword(s):  
Thermal Imaging ◽  
Chromatic Dispersion ◽  
Numerical Aperture ◽  
Chromatic Aberration ◽  
Average Intensity ◽  
Geometric Phases ◽  
Practical Applications ◽  
Chromatic Aberrations ◽  
Fabrication Costs ◽  
General Method

Longwave infrared (LWIR) optics are essential for several technologies, such as thermal imaging and wireless communication, but their development is hindered by their bulk and high fabrication costs. Metasurfaces have recently emerged as powerful platforms for LWIR integrated optics; however, conventional metasurfaces are highly chromatic, which adversely affects their performance in broadband applications. In this work, the chromatic dispersion properties of metasurfaces are analyzed via ray tracing, and a general method for correcting chromatic aberrations of metasurfaces is presented. By combining the dynamic and geometric phases, the desired group delay and phase profiles are imparted to the metasurfaces simultaneously, resulting in good achromatic performance. Two broadband achromatic metasurfaces based on all-germanium platforms are demonstrated in the LWIR : a broadband achromatic metalens with a numerical aperture of 0.32, an average intensity efficiency of 31%, and a Strehl ratio above 0.8 from 9.6 μm to 11.6 μm, and a broadband achromatic metasurface grating with a constant deflection angle of 30° from 9.6 μm to 11.6 μm. Compared with state-of-the-art chromatic-aberration-restricted LWIR metasurfaces, this work represents a substantial advance and brings the field a step closer to practical applications.

The Reduction of Chromatic Aberrations Due to Instrumental Instabilities

1971 ◽  
Vol 29 ◽  
pp. 14-15
Author(s):  
J. S. Lally ◽  
R. Evans
Keyword(s):  
Electron Microscope ◽  
High Voltage ◽  
Focal Length ◽  
Chromatic Aberration ◽  
Objective Lens ◽  
Usual Practice ◽  
Voltage Electron ◽  
Short Focal Length ◽  
Chromatic Aberrations ◽  
Electron Microscopes

One of the instrumental factors often limiting the resolution of the electron microscope is image defocussing due to changes in accelerating voltage or objective lens current. This factor is particularly important in high voltage electron microscopes both because of the higher voltages and lens currents required but also because of the inherently longer focal lengths, i.e. 6 mm in contrast to 1.5-2.2 mm for modern short focal length objectives.The usual practice in commercial electron microscopes is to design separately stabilized accelerating voltage and lens supplies. In this case chromatic aberration in the image is caused by the random and independent fluctuations of both the high voltage and objective lens current.

New Aspects in the Design of Electron Optical Magnification Systems

1972 ◽  
Vol 30 ◽  
pp. 606-607
Author(s):  
Willem H.J. Andersen
Keyword(s):  
Electron Microscope ◽  
Imaging System ◽  
Chromatic Aberration ◽  
Research Tool ◽  
Energy Losses ◽  
Objective Lens ◽  
Theoretical Limit ◽  
Optical Magnification ◽  
Chromatic Aberrations ◽  
High Degree

Electron microscope design, and particularly the design of the imaging system, has reached a high degree of perfection. Present objective lenses perform up to their theoretical limit, while the whole imaging system, consisting of three or four lenses, provides very wide ranges of magnification and diffraction camera length with virtually no distortion of the image. Evolution of the electron microscope in to a routine research tool in which objects of steadily increasing thickness are investigated, has made it necessary for the designer to pay special attention to the chromatic aberrations of the magnification system (as distinct from the chromatic aberration of the objective lens). These chromatic aberrations cause edge un-sharpness of the image due to electrons which have suffered energy losses in the object.There exist two kinds of chromatic aberration of the magnification system; the chromatic change of magnification, characterized by the coefficient Cm, and the chromatic change of rotation given by Cp.

Toward The Simultaneous Correction of Spherical and Chromatic Aberration in Electron Optics by Means of an Electrostatic Electron Mirror

1990 ◽  
Vol 48 (1) ◽  
pp. 206-207
Author(s):  
Gertrude. F. Rempfer
Keyword(s):  
Chromatic Aberration ◽  
Transverse Magnetic ◽  
Objective Lens ◽  
Ion Imaging ◽  
Corrected Image ◽  
Electric And Magnetic Fields ◽  
Chromatic Aberrations ◽  
Improved Performance ◽  
Electron Microscopes ◽  
Image Planes

Optimum performance in electron and ion imaging instruments, such as electron microscopes and probe-forming instruments, in most cases depends on a compromise either between imaging errors due to spherical and chromatic aberrations and the diffraction error or between the imaging errors and the current in the image. These compromises result in the use of very small angular apertures. Reducing the spherical and chromatic aberration coefficients would permit the use of larger apertures with resulting improved performance, granted that other problems such as incorrect operation of the instrument or spurious disturbances do not interfere. One approach to correcting aberrations which has been investigated extensively is through the use of multipole electric and magnetic fields. Another approach involves the use of foil windows. However, a practical system for correcting spherical and chromatic aberration is not yet available.Our approach to correction of spherical and chromatic aberration makes use of an electrostatic electron mirror. Early studies of the properties of electron mirrors were done by Recknagel. More recently my colleagues and I have studied the properties of the hyperbolic electron mirror as a function of the ratio of accelerating voltage to mirror voltage. The spherical and chromatic aberration coefficients of the mirror are of opposite sign (overcorrected) from those of electron lenses (undercorrected). This important property invites one to find a way to incorporate a correcting mirror in an electron microscope. Unfortunately, the parts of the beam heading toward and away from the mirror must be separated. A transverse magnetic field can separate the beams, but in general the deflection aberrations degrade the image. The key to avoiding the detrimental effects of deflection aberrations is to have deflections take place at image planes. Our separating system is shown in Fig. 1. Deflections take place at the separating magnet and also at two additional magnetic deflectors. The uncorrected magnified image formed by the objective lens is focused in the first deflector, and relay lenses transfer the image to the separating magnet. The interface lens and the hyperbolic mirror acting in zoom fashion return the corrected image to the separating magnet, and the second set of relay lenses transfers the image to the final deflector, where the beam is deflected onto the projection axis.

scholarly journals INVESTIGATION INTO THE BEHAVIOUR AND MODELLING OF CHROMATIC ABERRATIONS IN NON-METRIC DIGITAL CAMERAS

2019 ◽  
Vol XLII-2/W18 ◽  
pp. 99-106 ◽  
Author(s):  
D. D. Lichti ◽  
D. Jarron ◽  
M. Shahbazi ◽  
P. Helmholz ◽  
R. Radovanovic
Keyword(s):  
Digital Camera ◽  
Chromatic Aberration ◽  
Bundle Adjustment ◽  
Lens Distortion ◽  
Digital Cameras ◽  
Principal Point ◽  
Common Object ◽  
Chromatic Aberrations ◽  
The Impact ◽  
Orientation Parameters

Abstract. Chromatic aberration in colour digital camera imagery can affect the accuracy of photogrammetric reconstruction. Both longitudinal and transverse chromatic aberrations can be effectively modelled by making separate measurements in each of the blue, green and red colour bands and performing a specialized self-calibrating bundle adjustment. This paper presents the results of an investigation with two aims. The first aim is to quantify the presence of chromatic aberration in two sets of cameras: the six individual cameras comprising a Ladybug5 system, calibrated simultaneously in air; and four GoPro Hero 5 cameras calibrated independently under water. The second aim is to investigate the impacts of imposing different constraints in the self-calibration adjustment. To this end, four different adjustment cases were performed for all ten cameras: independent adjustment of the observations from each colour band; combined adjustment of all colour bands’ observations with common object points; combined adjustment of all colour bands with common object points and common exterior orientation parameters for each colour band triplet; and combined adjustment with common object points and certain common interior orientation parameters. The results show that the Ladybug5 cameras exhibit a small (1-2 pixel) amount of transverse chromatic aberration but no longitudinal chromatic aberration. The GoPro Hero 5 cameras exhibit significant (25 pixel) transverse chromatic aberration as well as longitudinal chromatic aberration. The principal distance was essentially independent of the adjustment case for the Ladybug5, but it was not for the GoPro Hero 5. The principal point position and precision were both affected considerably by adjustment case. Radial lens distortion was invariant to the adjustment case. The impact of adjustment case on decentring distortion was minimal in both cases.

scholarly journals High-efficiency broadband achromatic metalens for near-IR biological imaging window

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Yujie Wang ◽  
Qinmiao Chen ◽  
Wenhong Yang ◽  
Ziheng Ji ◽  
Limin Jin ◽  
...  
Keyword(s):  
Titanium Dioxide ◽  
Large Scale ◽  
Near Infrared ◽  
High Efficiency ◽  
Numerical Aperture ◽  
Biological Imaging ◽  
Material Loss ◽  
Practical Applications ◽  
Aspect Ratios ◽  
Polarization Insensitive

AbstractOver the past years, broadband achromatic metalenses have been intensively studied due to their great potential for applications in consumer and industry products. Even though significant progress has been made, the efficiency of technologically relevant silicon metalenses is limited by the intrinsic material loss above the bandgap. In turn, the recently proposed achromatic metalens utilizing transparent, high-index materials such as titanium dioxide has been restricted by the small thickness and showed relatively low focusing efficiency at longer wavelengths. Consequently, metalens-based optical imaging in the biological transparency window has so far been severely limited. Herein, we experimentally demonstrate a polarization-insensitive, broadband titanium dioxide achromatic metalens for applications in the near-infrared biological imaging. A large-scale fabrication technology has been developed to produce titanium dioxide nanopillars with record-high aspect ratios featuring pillar heights of 1.5 µm and ~90° vertical sidewalls. The demonstrated metalens exhibits dramatically increased group delay range, and the spectral range of achromatism is substantially extended to the wavelength range of 650–1000 nm with an average efficiency of 77.1%–88.5% and a numerical aperture of 0.24–0.1. This research paves a solid step towards practical applications of flat photonics.

Magnetic microlens focusing of electron beams

1992 ◽  
Vol 50 (2) ◽  
pp. 952-953 ◽  
Author(s):  
B. D. Terris ◽  
D. Rugar
Keyword(s):  
Permanent Magnets ◽  
Electron Beams ◽  
Focal Length ◽  
Chromatic Aberration ◽  
Emission Angle ◽  
Emission Sources ◽  
High Brightness ◽  
Chromatic Aberrations ◽  
Image Position ◽  
Initial Results

Recently, field emission sources in combination with either magnetic or electrostatic microlenses have been predicted to produce electron beams with high brightness and low aberrations. The key advantage to such systems is the short focal length and thus small coefficients of spherical and chromatic aberration. In addition, by using either small apertures or extremely sharp emission sources, the emission angle can be made small and thus the effect of the aberrations reduced further. We present here our initial results on building a magnetic microlens system. The unique feature of this work is the use of permanent magnets as the sole focusing elements in the lens, resulting in an extremely simple and inexpensive system.It has been shown that the aberrations in a focused electron beam can be reduced by selectively scaling the column dimensions. The focused spot sized is limited by the spherical aberrations,and the chromatic aberrations

Resolution and contrast enhancement on biological specimens by means of electron spectroscopic imaging (ESI)

1986 ◽  
Vol 44 ◽  
pp. 68-69
Author(s):  
U. B. Hezel ◽  
R. Bauer ◽  
E. Zellmann ◽  
W. I. Miller
Keyword(s):  
Heavy Metals ◽  
Heavy Metal ◽  
Electron Beam ◽  
Contrast Enhancement ◽  
Electron Scattering ◽  
Biological Material ◽  
Spectroscopic Imaging ◽  
Chromatic Aberration ◽  
Electron Spectroscopic Imaging ◽  
Chromatic Aberrations

The main elemental constituents of biological material - C,H,N,O - are the same elements found in typical embedding materials. Because of this the contrast of unstained biological material is very poor. Additionally, electron scattering by low Z atoms is mainly inelastic resulting in unsharp images from the concomitant chromatic aberration.These effects have been delt with by employing stains of such heavy metals as Os, U, or Pb. These stains are for the most part located at the biological structures themselves and primarily scatter the electron beam elastically. Thus with ultra-thin (<80nm) heavy metal stained sections of biological material the contrast in the CTEM is very good and chromatic aberrations are negligable.

scholarly journals Some experiments concerning the counting of scintillations produced by alpha particles.—Part III. Practical applications

1929 ◽  
Vol 122 (789) ◽  
pp. 335-352 ◽  
Keyword(s):  
Numerical Aperture ◽  
Alpha Particles ◽  
Resolving Power ◽  
Applied Physics ◽  
Practical Applications ◽  
First Case ◽  
Definition Of ◽  
At Will ◽  
Number Of Particles

There are two important characteristics of the microscope or any other optical system used for scintillation counting, which may influence the number observed, namely, the numerical aperture and the magnification. In order to show clearly the role of each factor it seemed desirable to investigate how the percentage of the number of particles observed varied with the numerical aperture in two cases where the magnification was widely different. The first case chosen was the counting of scintillations with a microscope of magnification 50, where the numerical aperture could be varied at will by placing stops on the objective. Stops of black paper which fitted the objective and could be easily interchanged in the dark were used. The numerical aperture corresponding to each objective stop was measured in the usual way (see, for example, ‘Dictionary of Applied Physics,’ vol. 4, p. 205 (1923)). The importance of the numerical aperture is not due to its influence on resolving power, but to its influence on the fraction of the light from a scintillation which enters the objective. From the definition of numerical aperture it follows that the fraction of the light entering the objective from the object viewed is ½ (1 — √ 1— ( n.a ) 2 ).

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