Experimental study on the restoration from a tilt-azimuth series for improvement in resolution

1995 ◽  
Vol 53 ◽  
pp. 636-637
Author(s):  
Norio Baba ◽  
Norihiko Ichise ◽  
Syunya Watanabe
Keyword(s):  
Experimental Study ◽  
Spherical Aberration ◽  
Incident Beam ◽  
Optical Parameters ◽  
Beam Tilting ◽  
Illumination Method ◽  
Restoration Method ◽  
Illumination Mode

The tilted beam illumination method is used to improve the resolution comparing with the axial illumination mode. Using this advantage, a restoration method of several tilted beam images covering the full azimuthal range was proposed by Saxton, and experimentally examined. To make this technique more reliable it seems that some practical problems still remain. In this report the restoration was attempted and the problems were considered. In our study, four problems were pointed out for the experiment of the restoration. (1) Accurate beam tilt adjustment to fit the incident beam to the coma-free axis for the symmetrical beam tilting over the full azimuthal range. (2) Accurate measurements of the optical parameters which are necessary to design the restoration filter. Even if the spherical aberration coefficient Cs is known with accuracy and the axial astigmatism is sufficiently compensated, at least the defocus value must be measured. (3) Accurate alignment of the tilt-azimuth series images.

Resolution Attainable With the Present Day STEM

1973 ◽  
Vol 31 ◽  
pp. 230-231 ◽  
Author(s):  
J. S. Wall ◽  
J. P. Langmore ◽  
H. Isaacson ◽  
A. V. Crewe
Keyword(s):  
Spherical Aberration ◽  
Focal Length ◽  
Incident Beam ◽  
Scanning Transmission Electron Microscope ◽  
Aperture Size ◽  
Magnetic Lens ◽  
Peak Intensity ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Half Angle

The scanning transmission electron microscope (STEM) constructed by the authors employs a field emission gun and a 1.15 mm focal length magnetic lens to produce a probe on the specimen. The aperture size is chosen to allow one wavelength of spherical aberration at the edge of the objective aperture. Under these conditions the profile of the focused spot is expected to be similar to an Airy intensity distribution with the first zero at the same point but with a peak intensity 80 per cent of that which would be obtained If the lens had no aberration. This condition is attained when the half angle that the incident beam subtends at the specimen, 𝛂 = (4𝛌/Cs)¼

Ultra-high resolution SEMI-in-lens type FE-SEM, JSM-6320F, with strong magnetic-field lens with built-in secondary-electron detector

1994 ◽  
Vol 52 ◽  
pp. 484-485
Author(s):  
T. Miyokawa ◽  
H. Kazumori ◽  
S. Nakagawa ◽  
C. Nielsen
Keyword(s):  
High Resolution ◽  
Secondary Electron ◽  
Spherical Aberration ◽  
Incident Beam ◽  
Chromatic Aberration ◽  
Magnetic Flux Density ◽  
Objective Lens ◽  
Electron Detector ◽  
High Resolution Images ◽  
Working Distance

We have developed a strongly excited objective lens with a built-in secondary electron detector to provide ultra-high resolution images with high quality at low to medium accelerating voltages. The JSM-6320F is a scanning electron microscope (FE-SEM) equipped with this lens and an incident beam divergence angle control lens (ACL).The objective lens is so strongly excited as to have peak axial Magnetic flux density near the specimen surface (Fig. 1). Since the speciien is located below the objective lens, a large speciien can be accomodated. The working distance (WD) with respect to the accelerating voltage is limited due to the magnetic saturation of the lens (Fig.2). The aberrations of this lens are much smaller than those of a conventional one. The spherical aberration coefficient (Cs) is approximately 1/20 and the chromatic aberration coefficient (Cc) is 1/10. for accelerating voltages below 5kV. At the medium range of accelerating voltages (5∼15kV). Cs is 1/10 and Cc is 1/7. Typical values are Cs-1.lmm. Cc=l. 5mm at WD=2mm. and Cs=3.lmm. Cc=2.9 mm at WD=5mm. This makes the lens ideal for taking ultra-high resolution images at low to medium accelerating voltages.

scholarly journals Ocular wavefront aberrations in acute central serous chorioretinopathy

2021 ◽  
Vol 9 (1) ◽  
pp. 33-33
Author(s):  
Banafsheh Kharrazi Ghadim ◽  
Nazli Taheri ◽  
Mohammad Reza Niyousha
Keyword(s):  
Visual Acuity ◽  
Root Mean Square ◽  
Central Serous Chorioretinopathy ◽  
Spherical Aberration ◽  
Optical Parameters ◽  
Average Height ◽  
Mean Square ◽  
Pupillary Dilation ◽  
Foveal Thickness ◽  
Wavefront Aberrations

Background: Central serous chorioretinopathy (CSCR) is a condition of choroidal and retinal pathologies that may affect vision, so we assessed vision by the ocular wavefront in the acute form of CSCR. Methods: This cross-sectional study included 21 cases (16-male, 5-female) of acute onset CSCR was referred to the retina clinic of Nikookari Eye Hospital. Visual acuity and ocular examination with and without pupillary dilation record. Central macular thickness and sub-foveal fluid height of all patients measured by spectral-domain optical coherence tomography (SD-OCT). All of them fulfilled binocular visual function analyzer by Tracy Technology after complete pupillary dilation. The items such as spherical equivalent, total root mean square, total lower-order aberration, total higher-order aberration, defocus, astigmatism, secondary astigmatism, coma, spherical aberration, trefoil, Strehl ratio in point spread function, the average height in the modulation transfer function, and root mean square error registered. Generalized Estimation Equations (GEE) were used to compare two groups of affected CSCR and normal contralateral eyes. Results: The mean uncorrected distance visual acuity in the CSCR eyes is (Decimal Notation) 0.82±0.17 and in the contralateral eyes is 0.95±0.09 (P=0.002). Analysis of macular OCT data CSCR group represents: central foveal thickness 485.9±165.12 μm and mean fluid height 284.3±165.42 μm. The mentioned optical parameters of ocular wavefront aberrations do not have significantly different results in the two groups. Conclusion: Our study showed CSCR reduced uncorrected visual acuity but it did not detect significant ocular wavefront changes in acute CSCR

Hollow-cone illumination in simulated ADF STEM

1989 ◽  
Vol 47 ◽  
pp. 124-125
Author(s):  
R. F. Loane ◽  
J. Silcox
Keyword(s):  
Stationary Phase ◽  
Spherical Aberration ◽  
Image Interpretation ◽  
Incident Beam ◽  
Bragg Angle ◽  
Hollow Cone ◽  
Fringe Contrast ◽  
Convergence Angle ◽  
Probe Size ◽  
Overlap Region

The overlap regions between CBED disks are a source of lattice fringe contrast in ADF STEM images of crystals. For sufficiently small lattice spacings, the Scherzer focus convergence angle is too small for the CBED disks to overlap, and the lattice is not visible. By increasing the convergence angle beyond the Scherzer angle to create an overlap region, and by using stationary phase defocus, smaller lattices can be imaged However, with larger convergence angles, lens aberrations spread the incident beam and small aperiodic structures, such as adatoms, become difficult to image. If the specimen Bragg angle is known, an annular objective aperture can be designed to pass the overlap regions of the incident beam, while blocking the central, non-overlap region which produces a large constant background. The annular probe size is minimized by choosing an annulus width and defocus which balance the spherical aberration across the annulus (close to stationary phase defocus). Simulations indicate hollow cone illumination may allow both adatoms and smaller lattices to be imaged simultaneously. This approach presumes knowledge of the specimen, and must be used in conjunction with standard methods for correct image interpretation. An incorrectly applied annulus will produce image artifacts.

Heat Generation in Laser Irradiated Tissue

1989 ◽  
Vol 111 (1) ◽  
pp. 62-68 ◽  
Author(s):  
A. J. Welch ◽  
J. A. Pearce ◽  
K. R. Diller ◽  
G. Yoon ◽  
W. F. Cheong
Keyword(s):  
Heat Source ◽  
Heat Generation ◽  
Near Infrared ◽  
Scattered Light ◽  
Incident Beam ◽  
Accurate Estimation ◽  
Optical Parameters ◽  
Infrared Wavelengths ◽  
Improved Model

Many medical applications involving lasers rely upon the generation of heat within the tissue for the desired therapeutic effect. Determination of the absorbed light energy in tissue is difficult in many cases. Although UV wavelengths of the excimer laser and 10.6 μm wavelength of the CO2 laser are absorbed within the first 20 μm of soft tissue, visible and near infrared wavelengths are scattered as well as absorbed. Typically, multiple scattering is a significant factor in the distribution of light in tissue and the resulting heat source term. An improved model is presented for estimating heat generation due to the absorption of a collimated (axisymmetric) laser beam and scattered light at each point r and z in tissue. Heat generated within tissue is a function of the laser power, the shape and size of the incident beam and the optical properties of the tissue at the irradiation wavelength. Key to the calculation of heat source strength is accurate estimation of the light distribution. Methods for experimentally determining the optical parameters of tissue are discussed in the context of the improved model.

Theoretical and experimental study of the transmitted intensity as a function of thickness when the incident beam is parallel to a crystallographic axis

1978 ◽  
Vol 47 (1) ◽  
pp. 311-320 ◽  
Author(s):  
B. Yangui ◽  
M. Rekik ◽  
G. Nihoul-Boutang ◽  
C. Jouanin ◽  
C. Boulesteix ◽  
...  
Keyword(s):  
Experimental Study ◽  
Incident Beam ◽  
Crystallographic Axis ◽  
Transmitted Intensity

scholarly journals Changes in functional, anatomical and optical parameters of the eye in children with habitually excessive accommodation stress and pseudomyopia after regular badminton playing

2019 ◽  
Vol 12 (4) ◽  
pp. 51-63
Author(s):  
E. P. Tarutta ◽  
N. A. Tarasova ◽  
G. A. Markosian ◽  
S. V. Milash ◽  
S. G. Harutyunyan ◽  
...  
Keyword(s):  
Blood Flow ◽  
Visual Acuity ◽  
Choroidal Thickness ◽  
Ophthalmic Artery ◽  
Spherical Aberration ◽  
Blood Flow Rate ◽  
Optical Parameters ◽  
Manifest Refraction ◽  
Uncorrected Visual Acuity ◽  
Retinal Artery

Purpose. To study the state of refraction, accommodation, and blood flow in eye vessels of children with habitually excessive accommodation stress (HEAS) and pseudomyopia practicing badminton.Material and methods. The study involved 11 patients (20 eyes) aged 7 to 11 years (average M±SD: 9.24 ± 1.06 years) with pseudomyopia and HEAS: 4 patients with myopia (7 eyes), 3 children with hyperopia (6 eyes), 4 children with emmetropia (7 eyes) before they started practicing badminton and after playing it for a certain time. All patients were tested for visual acuity, subjective and objective accommodation, optical biometry, aberrometry, velocity of blood flow in eye vessels, and choroidal thickness.Results. After 1 year of regular badminton workout, the subjects revealed a 0.92 ± 0.82 D weakening of manifest refraction, a decrease in accommodation tone by 0.85 ± 0.77 D, an increase in blood flow rate in ophthalmic artery and the central retinal artery, an increase in positive spherical aberration, a decrease in aberrations associated with mismatch and irregularity ofoptical system elements (tilt, trefoil, coma), which indirectly indicates a strengthening of the ligamentous apparatus of the lens.Conclusion. Practicing sports (badminton) contributes to the elimination of pseudomyopia, improvement of uncorrected visual acuity, accommodative ability, and ophthalmic hemodynamics indicators.

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