Spot size of the radar return from a radar-acoustic sounding system (RASS) due to atmospheric refractive turbulence

Radio Science ◽  
1978 ◽  
Vol 13 (6) ◽  
pp. 985-989 ◽  
Author(s):  
S. F. Clifford ◽  
Ting-i Wang ◽  
J. T. Priestley
Keyword(s):  
Spot Size ◽  
Acoustic Sounding

Remarks on the application of backscattered electron imaging (BEI) to the scanning electron microscopy (SEM) of biological structures

1983 ◽  
Vol 41 ◽  
pp. 484-487
Author(s):  
Etienne de Harven
Keyword(s):  
High Resolution ◽  
Incident Beam ◽  
Spot Size ◽  
Primary Electron ◽  
Critical Point Drying ◽  
Cell Shapes ◽  
High Resolution Images ◽  
Backscattered Electron ◽  
Electron Imaging ◽  
Scanning Electron

Biological ultrastructures have been extensively studied with the scanning electron microscope (SEM) for the past 12 years mainly because this instrument offers accurate and reproducible high resolution images of cell shapes, provided the cells are dried in ways which will spare them the damage which would be caused by air drying. This can be achieved by several techniques among which the critical point drying technique of T. Anderson has been, by far, the most reproducibly successful. Many biologists, however, have been interpreting SEM micrographs in terms of an exclusive secondary electron imaging (SEI) process in which the resolution is primarily limited by the spot size of the primary incident beam. in fact, this is not the case since it appears that high resolution, even on uncoated samples, is probably compromised by the emission of secondary electrons of much more complex origin.When an incident primary electron beam interacts with the surface of most biological samples, a large percentage of the electrons penetrate below the surface of the exposed cells.

A High Resolution Scanning Microscope

1968 ◽  
Vol 26 ◽  
pp. 356-357
Author(s):  
A. V. Crewe ◽  
J. Wall ◽  
L. M. Welter
Keyword(s):  
High Resolution ◽  
Field Emission ◽  
Spherical Aberration ◽  
Focal Length ◽  
Spot Size ◽  
Emission Source ◽  
Field Of View ◽  
Scanning Microscope ◽  
Magnetic Lens ◽  
High Quality

A scanning microscope using a field emission source has been described elsewhere. This microscope has now been improved by replacing the single magnetic lens with a high quality lens of the type described by Ruska. This lens has a focal length of 1 mm and a spherical aberration coefficient of 0.5 mm. The final spot size, and therefore the microscope resolution, is limited by the aberration of this lens to about 6 Å.The lens has been constructed very carefully, maintaining a tolerance of + 1 μ on all critical surfaces. The gun is prealigned on the lens to form a compact unit. The only mechanical adjustments are those which control the specimen and the tip positions. The microscope can be used in two modes. With the lens off and the gun focused on the specimen, the resolution is 250 Å over an undistorted field of view of 2 mm. With the lens on,the resolution is 20 Å or better over a field of view of 40 microns. The magnification can be accurately varied by attenuating the raster current.

Image registration with a computer driven S.T.E.M.

1978 ◽  
Vol 36 (1) ◽  
pp. 98-99
Author(s):  
A.M.H. Schepman ◽  
J.A.P. van der Voort ◽  
J.E. Mellema
Keyword(s):  
Spot Size ◽  
Scanning Transmission Electron Microscope ◽  
Small Computer ◽  
Structural Studies ◽  
Area Of Interest ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Specimen Area ◽  
On Line ◽  
Minimum Distances

A Scanning Transmission Electron Microscope (STEM) was coupled to a small computer. The system (see Fig. 1) has been built using a Philips EM400, equipped with a scanning attachment and a DEC PDP11/34 computer with 34K memory. The gun (Fig. 2) consists of a continuously renewed tip of radius 0.2 to 0.4 μm of a tungsten wire heated just below its melting point by a focussed laser beam (1). On-line operation procedures were developped aiming at the reduction of the amount of radiation of the specimen area of interest, while selecting the various imaging parameters and upon registration of the information content. Whereas the theoretical limiting spot size is 0.75 nm (2), routine resolution checks showed minimum distances in the order 1.2 to 1.5 nm between corresponding intensity maxima in successive scans. This value is sufficient for structural studies of regular biological material to test the performance of STEM over high resolution CTEM.

Ultra-spatially resolved synchrotron powered FT-IR microspectroscopy of individual cells of biological material

1995 ◽  
Vol 53 ◽  
pp. 884-885
Author(s):  
David L. Wetzel ◽  
John A. Reffner ◽  
Gwyn P. Williams
Keyword(s):  
Thermal Noise ◽  
Spot Size ◽  
Acquisition Time ◽  
Thermal Source ◽  
Signal To Noise ◽  
Spatially Resolved ◽  
Good Spatial Resolution ◽  
Small Spot ◽  
Ft Ir ◽  
Ir Microspectroscopy

Synchrotron radiation is 100 to 1000 times brighter than a thermal source such as a globar. It is not accompanied with thermal noise and it is highly directional and nondivergent. For these reasons, it is well suited for ultra-spatially resolved FT-IR microspectroscopy. In efforts to attain good spatial resolution in FT-IR microspectroscopy with a thermal source, a considerable fraction of the infrared beam focused onto the specimen is lost when projected remote apertures are used to achieve a small spot size. This is the case because of divergence in the beam from that source. Also the brightness is limited and it is necessary to compromise on the signal-to-noise or to expect a long acquisition time from coadding many scans. A synchrotron powered FT-IR Microspectrometer does not suffer from this effect. Since most of the unaperatured beam’s energy makes it through even a 12 × 12 μm aperture, that is a starting place for aperture dimension reduction.

Electron Channelling Contrast Imaging of Dislocations

1990 ◽  
Vol 48 (1) ◽  
pp. 600-601
Author(s):  
J.T. Czernuszka ◽  
N.J. Long ◽  
P.B. Hirsch
Keyword(s):  
Field Emission ◽  
Secondary Electron ◽  
Surface Defects ◽  
Spot Size ◽  
Beam Divergence ◽  
Contrast Imaging ◽  
Scattered Electron ◽  
Near Surface ◽  
Filter System ◽  
Electron Channelling

In the 1970s there was considerable interest in the development of the electron channelling contrast imaging (ECCI) technique for imaging near surface defects in bulk (electron opaque) specimens. The predictions of the theories were realised experimentally by Morin et al., who used a field emission gun (FEG) operating at 40-50kV and an energy filter such that only electrons which had lost no more than a few 100V were detected. This paper presents the results of a set of preliminary experiments which show that an energy filter system is unneccessary to image and characterise the Burgers vectors of dislocations in bulk specimens. The examples in the paper indicatethe general versatility of the technique.A VG HB501 STEM with a FEG was operated at 100kV. A single tilt cartridge was used in the reflection position of the microscope. A retractable back-scattered electron detector was fitted into the secondary electron port and positioned to within a few millimetres of the specimen. The image was acquired using a Synoptics Synergy framestore and digital scan generator and subsequently processed using Semper 6. The beam divergence with the specimen in this position was 2.5 mrads with a spot size of approximately 4nm. Electron channelling patterns were used to orientate the sample.

Microspectroscopy Using a Solid Immersion Lens

2001 ◽  
Vol 7 (S2) ◽  
pp. 148-149
Author(s):  
C.D. Poweleit ◽  
J Menéndez
Keyword(s):  
Spatial Resolution ◽  
Focal Plane ◽  
Numerical Aperture ◽  
Normal Incidence ◽  
Spot Size ◽  
Index Of Refraction ◽  
Objective Lens ◽  
Improvement Factor ◽  
Oil Immersion ◽  
Long Time

Oil immersion lenses have been used in optical microscopy for a long time. The light’s wavelength is decreased by the oil’s index of refraction n and this reduces the minimum spot size. Additionally, the oil medium allows a larger collection angle, thereby increasing the numerical aperture. The SIL is based on the same principle, but offers more flexibility because the higher index material is solid. in particular, SILs can be deployed in cryogenic environments. Using a hemispherical glass the spatial resolution is improved by a factor n with respect to the resolution obtained with the microscope’s objective lens alone. The improvement factor is equal to n2 for truncated spheres.As shown in Fig. 1, the hemisphere SIL is in contact with the sample and does not affect the position of the focal plane. The focused rays from the objective strike the lens at normal incidence, so that no refraction takes place.

Computational Technique for the Qualification of Focal Spot Size and Shape of Industrial Radioscopy Equipment Using Star Patterns

2020 ◽  
Vol 78 (4) ◽  
pp. 479-486
Author(s):  
Marcela Tatiana Fernandes Beserra ◽  
◽  
Ricardo Tadeu Lopes ◽  
Davi Ferreira de Oliveira ◽  
Claudio Carvalho Conti ◽  
...  
Keyword(s):  
Focal Spot ◽  
Spot Size ◽  
Computational Technique ◽  
Focal Spot Size ◽  
Size And Shape

Wide-Tuning-Wavelength-Range LGLC Laser with Low-Loss Dual-Core Spot Size Converter

2012 ◽  
Vol E95.C (7) ◽  
pp. 1272-1275
Author(s):  
Takanori SUZUKI ◽  
Hideo ARIMOTO ◽  
Takeshi KITATANI ◽  
Aki TAKEI ◽  
Takafumi TANIGUCHI ◽  
...  
Keyword(s):  
Wavelength Range ◽  
Spot Size ◽  
Low Loss ◽  
Dual Core
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