High Resolution through Graded-Index Microoptics

By solving Helmholtz equations, relationships to describe propagating modes in an arbitrary graded-index planar waveguide are derived. We show that in the quadratic- and secant-index waveguides a minimal mode width is 0.4λ/n, where λ is the wavelength in free space and n is the refractive index on the fiber axis. By modeling in FullWAVE, we show that the high-resolution imaging can be achieved with half-pitch graded-index Mikaelian microlenses (ML) and Maxwell’s “fisheye” lenses. It is shown that using a 2D ML, the point source can be imaged near the lens surface as a light spot with the full width at half maximum (FWHM) of 0.12λ. This value is close to the diffraction limit for silicon (n=3.47) in 2D media FWHM=0.44λ/n=0.127λ. We also show that half-pitch ML is able to resolve at half-maximum two close point sources separated by a 0.3λ distance.

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Super-resolution imaging of negative-refractive graded-index photonic crystal flat lens

Materials Research Express ◽

10.1088/2053-1591/ac4731 ◽

2021 ◽

Author(s):

Binming Liang ◽

Xiao Huang ◽

Jihong Zheng

Keyword(s):

Photonic Crystal ◽

Imaging System ◽

Super Resolution ◽

Point Sources ◽

Image Resolution ◽

Multiple Point ◽

Single Image ◽

Graded Index ◽

Resolution Imaging ◽

Flat Lens

Abstract Photonic crystal (PC) not only breaks through the diffraction limit of traditional lenses but also can realize super-resolution imaging. Improving the resolution is the key task of PC imaging. The main work of this paper is to use a graded-index Photonic crystal (GPC) flat lens to improve the image resolution. An air-hole type two-dimensional (2D) GPC structure based on silicon medium is proposed in this paper. Numerical simulations through RSoft reveal that when the medium in the imaging area is air, the full width at half maximum (FWHM) value of a single image reaches 0.362λ. According to the Rayleigh criterion, the images of two point sources 0.57λ apart can also be distinguished. In the imaging system composed of cedar oil and GPC flat lens, the FWHM value of a single image reaches 0.34λ. In addition, the images of multiple point sources 0.49λ apart can still be distinguished.

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High Resolution Imaging Forty Years Ago

Symposium - International Astronomical Union ◽

10.1017/s0074180900107855 ◽

1994 ◽

Vol 158 ◽

pp. 337-341

Author(s):

R. C. Jennison

Keyword(s):

High Resolution ◽

Point Sources ◽

Resolving Power ◽

High Angular Resolution ◽

Electromagnetic Spectrum ◽

High Resolution Imaging ◽

Resolution Imaging ◽

Optical Telescopes ◽

Very High ◽

Better Than

This conference is concerned with the very high resolution imaging of cosmic sources in many parts of the electromagnetic spectrum. Various techniques are now available and the equipment is often automated and highly sophisticated but the term ‘very high angular resolution’ is comparative. Many of the problems existed over forty years ago when the best resolving power was about half a degree and the two major radio ‘stars’ appeared to be point sources. Very high resolution imaging in those days was the struggle to reach one minute of arc and Hanbury Brown had set his sights on considerably better than one second of arc with the concept of the intensity interferometer. The dream was to achieve a resolving power comparable to that of optical telescopes.

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Alternative approaches to ultra-high resolution imaging

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100087562 ◽

1991 ◽

Vol 49 ◽

pp. 650-651

Author(s):

J.M. Cowley

Keyword(s):

High Resolution ◽

High Voltage ◽

High Resolution Electron Microscopy ◽

Crystal Defects ◽

High Resolution Imaging ◽

General Applicability ◽

Resolution Electron ◽

Radiation Resistant ◽

Resolution Imaging ◽

Alternative Approaches

By extrapolation of past experience, it would seem that the future of ultra-high resolution electron microscopy rests with the advances of electron optical engineering that are improving the instrumental stability of high voltage microscopes to achieve the theoretical resolutions of 1Å or better at 1MeV or higher energies. While these high voltage instruments will undoubtedly produce valuable results on chosen specimens, their general applicability has been questioned on the basis of the excessive radiation damage effects which may significantly modify the detailed structures of crystal defects within even the most radiation resistant materials in a period of a few seconds. Other considerations such as those of cost and convenience of use add to the inducement to consider seriously the possibilities for alternative approaches to the achievement of comparable resolutions.

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Principle and practice of high-resolution imaging with a field-emission TEM

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100121090 ◽

1992 ◽

Vol 50 (1) ◽

pp. 138-139

Author(s):

Max T. Otten ◽

Wim M.J. Coene

Keyword(s):

High Resolution ◽

Field Emission ◽

Incidence Angle ◽

Temporal Coherence ◽

Energy Spread ◽

High Resolution Imaging ◽

Major Improvement ◽

High Resolution Images ◽

Resolution Imaging

High-resolution imaging with a LaB6 instrument is limited by the spatial and temporal coherence, with little contrast remaining beyond the point resolution. A Field Emission Gun (FEG) reduces the incidence angle by a factor 5 to 10 and the energy spread by 2 to 3. Since the incidence angle is the dominant limitation for LaB6 the FEG provides a major improvement in contrast transfer, reducing the information limit to roughly one half of the point resolution. The strong improvement, predicted from high-resolution theory, can be seen readily in diffractograms (Fig. 1) and high-resolution images (Fig. 2). Even if the information in the image is limited deliberately to the point resolution by using an objective aperture, the improved contrast transfer close to the point resolution (Fig. 1) is already worthwhile.

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Imaging of ferroelectric domain walls by electron holography

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100121636 ◽

1992 ◽

Vol 50 (1) ◽

pp. 246-247

Author(s):

Xiao Zhang

Keyword(s):

Magnetic Field ◽

High Resolution ◽

Domain Walls ◽

Ferroelectric Domain ◽

Object Wave ◽

Electron Holography ◽

High Resolution Imaging ◽

Quantitative Measurements ◽

Resolution Imaging ◽

Electron Microscopes

Electron holography has recently been available to modern electron microscopy labs with the development of field emission electron microscopes. The unique advantage of recording both amplitude and phase of the object wave makes electron holography a effective tool to study electron optical phase objects. The visibility of the phase shifts of the object wave makes it possible to directly image the distributions of an electric or a magnetic field at high resolution. This work presents preliminary results of first high resolution imaging of ferroelectric domain walls by electron holography in BaTiO3 and quantitative measurements of electrostatic field distribution across domain walls.

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The method of replication affects metal film granularity and resolution

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100155517 ◽

1989 ◽

Vol 47 ◽

pp. 708-709

Author(s):

George C. Ruben

Keyword(s):

Electron Beam ◽

High Resolution ◽

Film Thickness ◽

Single Molecule ◽

Metal Film ◽

Vertical Surface ◽

High Resolution Imaging ◽

Controllable Factors ◽

Resolution Imaging

Single molecule resolution in electron beam sensitive, uncoated, noncrystalline materials has been impossible except in thin Pt-C replicas ≤ 150Å) which are resistant to the electron beam destruction. Previously the granularity of metal film replicas limited their resolution to ≥ 20Å. This paper demonstrates that Pt-C film granularity and resolution are a function of the method of replication and other controllable factors. Low angle 20° rotary , 45° unidirectional and vertical 9.7±1 Å Pt-C films deposited on mica under the same conditions were compared in Fig. 1. Vertical replication had a 5A granularity (Fig. 1c), the highest resolution (table), and coated the whole surface. 45° replication had a 9Å granulartiy (Fig. 1b), a slightly poorer resolution (table) and did not coat the whole surface. 20° rotary replication was unsuitable for high resolution imaging with 20-25Å granularity (Fig. 1a) and resolution 2-3 times poorer (table). Resolution is defined here as the greatest distance for which the metal coat on two opposing faces just grow together, that is, two times the apparent film thickness on a single vertical surface.

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Nano-probe x-ray analysis and high-resolution imaging on planar defects in high-pressure synthesized infinite-layer superconductor

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100171377 ◽

1994 ◽

Vol 52 ◽

pp. 728-729

Author(s):

Y. Y. Wang ◽

H. Zhang ◽

V. P. Dravid ◽

H. Zhang ◽

L. D. Marks ◽

...

Keyword(s):

High Pressure ◽

High Resolution ◽

Atomic Structure ◽

Emission Spectra ◽

High Resolution Electron Microscopy ◽

Planar Defects ◽

X Ray ◽

Infinite Layer ◽

Resolution Electron ◽

Resolution Imaging

Azuma et al. observed planar defects in a high pressure synthesized infinitelayer compound (i.e. ACuO2 (A=cation)), which exhibits superconductivity at ~110 K. It was proposed that the defects are cation deficient and that the superconductivity in this material is related to the planar defects. In this report, we present quantitative analysis of the planar defects utilizing nanometer probe xray microanalysis, high resolution electron microscopy, and image simulation to determine the chemical composition and atomic structure of the planar defects. We propose an atomic structure model for the planar defects.Infinite-layer samples with the nominal chemical formula, (Sr1-xCax)yCuO2 (x=0.3; y=0.9,1.0,1.1), were prepared using solid state synthesized low pressure forms of (Sr1-xCax)CuO2 with additions of CuO or (Sr1-xCax)2CuO3, followed by a high pressure treatment.Quantitative x-ray microanalysis, with a 1 nm probe, was performed using a cold field emission gun TEM (Hitachi HF-2000) equipped with an Oxford Pentafet thin-window x-ray detector. The probe was positioned on the planar defects, which has a 0.74 nm width, and x-ray emission spectra from the defects were compared with those obtained from vicinity regions.

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Performance Evaluation of a Novel Type of Low-Energy Electron Microscope

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100180525 ◽

1990 ◽

Vol 48 (1) ◽

pp. 354-355

Author(s):

Bertholdand Senftinger ◽

Helmut Liebl

Keyword(s):

Electron Microscope ◽

High Resolution ◽

Field Strength ◽

Numerical Aperture ◽

Low Energy ◽

Energy Electron ◽

High Resolution Imaging ◽

Lens System ◽

Resolution Imaging ◽

Low Energy Electron

During the last few years the investigation of clean and adsorbate-covered solid surfaces as well as thin-film growth and molecular dynamics have given rise to a constant demand for high-resolution imaging microscopy with reflected and diffracted low energy electrons as well as photo-electrons. A recent successful implementation of a UHV low-energy electron microscope by Bauer and Telieps encouraged us to construct such a low energy electron microscope (LEEM) for high-resolution imaging incorporating several novel design features, which is described more detailed elsewhere.The constraint of high field strength at the surface required to keep the aberrations caused by the accelerating field small and high UV photon intensity to get an improved signal-to-noise ratio for photoemission led to the design of a tetrode emission lens system capable of also focusing the UV light at the surface through an integrated Schwarzschild-type objective. Fig. 1 shows an axial section of the emission lens in the LEEM with sample (28) and part of the sample holder (29). The integrated mirror objective (50a, 50b) is used for visual in situ microscopic observation of the sample as well as for UV illumination. The electron optical components and the sample with accelerating field followed by an einzel lens form a tetrode system. In order to keep the field strength high, the sample is separated from the first element of the einzel lens by only 1.6 mm. With a numerical aperture of 0.5 for the Schwarzschild objective the orifice in the first element of the einzel lens has to be about 3.0 mm in diameter. Considering the much smaller distance to the sample one can expect intense distortions of the accelerating field in front of the sample. Because the achievable lateral resolution depends mainly on the quality of the first imaging step, careful investigation of the aberrations caused by the emission lens system had to be done in order to avoid sacrificing high lateral resolution for larger numerical aperture.

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Comparison of ultra high resolution immersion lens CFESEM and TEM for imaging of semiconductor devices

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100176241 ◽

1990 ◽

Vol 48 (4) ◽

pp. 622-623

Author(s):

Terrence Reilly ◽

Al Pelillo ◽

Barbara Miner

Keyword(s):

High Resolution ◽

Sample Preparation ◽

Cross Sections ◽

Semiconductor Devices ◽

Ion Milling ◽

Observation Area ◽

Transmission Electron ◽

Milling Machines ◽

Resolution Imaging ◽

Electron Microscopes

The use of transmission electron microscopes (TEM) has proven to be very valuable in the observation of semiconductor devices. The need for high resolution imaging becomes more important as the devices become smaller and more complex. However, the sample preparation for TEM observation of semiconductor devices have generally proven to be complex and time consuming. The use of ion milling machines usually require a certain degree of expertise and allow a very limited viewing area. Recently, the use of an ultra high resolution "immersion lens" cold cathode field emission scanning electron microscope (CFESEM) has proven to be very useful in the observation of semiconductor devices. Particularly at low accelerating voltages where compositional contrast is increased. The Hitachi S-900 has provided comparable resolution to a 300kV TEM on semiconductor cross sections. Using the CFESEM to supplement work currently being done with high voltage TEMs provides many advantages: sample preparation time is greatly reduced and the observation area has also been increased to 7mm. The larger viewing area provides the operator a much greater area to search for a particular feature of interest. More samples can be imaged on the CFESEM, leaving the TEM for analyses requiring diffraction work and/or detecting the nature of the crystallinity.

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