Showing papers on "Contrast transfer function published in 2007"

Analysis of the effects of spherical aberration on ultrafast laser-induced refractive index variation in glass.

Abstract: We propose a comprehensive analysis of the effects that spherical aberration may have on the process of ultrafast laser photowriting in bulk transparent materials and discuss the consequences for the generated refractive index changes. Practical aspects for a longitudinal photowriting configuration are emphasized. Laser-induced index variation in BK7 optical glass and fused silica (a-SiO2) affected by spherical aberration are characterized experimentally using phase-contrast optical microscopy. Experimental data are matched by analytical equations describing light propagation through dielectric interfaces. Corrective solutions are proposed with a particular focus on the spatial resolution achievable and on the conditions to obtain homogeneously photo-induced waveguides in a longitudinal writing configuration.

Achieving 63 pm Resolution in Scanning Transmission Electron Microscope with Spherical Aberration Corrector

Abstract: The performance of a newly developed high-resolution 300 kV microscope equipped with a spherical aberration corrector for probe-forming systems is reported. This microscope gave the highest resolution for the distance between atomic columns, as determined by a high-angle annular dark field imaging method using a GaN[211] crystalline specimen, where the distance between the neighboring columns of Ga was 63 pm.

Influence of orientation on the contrast of high-angle annular dark-field images of silicon

Abstract: Atom column intensities of silicon single crystals oriented along different crystallographic orientations are compared in experimental and simulated high-angle annular dark-field images in scanning transmission electron microscopy. The intensity of a background, measured between the columns, is also evaluated and found to be largely independent of the column spacing. The contrast is lower in the experiments, and it has been suggested previously that this follows because the background is higher in the experiments. We explore the extent to which the comparison of experimental atom column intensities with image simulations is aided by subtraction of the background for these data. We also explore an alternative view: simple simulations overestimate the contrast because spatial incoherence and associated instabilities are not taken into account. The results do not distinguish between these approaches, which need not be in opposition, and we describe experiments which might further clarify matters. © 2007 The American Physical Society.

Resolution in Electron Tomography

Abstract: Traditionally, in computed tomography practiced in radiology, the resolution of the reconstruction is expressed in terms of the number of evenly spaced projections required for the faithful reconstruction of an object that has a given diameter (see equation (10) below).The tacit assumption is that projection data have a sufficient spectral signal-to-noise ratio (SSNR) in the whole frequency range in order to reproduce the object faithfully. In electron microscopy, the situation is dramatically different, as the electron dose limitations result in very low SSNR in the individual projections. The suppression of signal is particularly severe in high spatial frequencies, where the signal is affected by the envelope function of the microscope and the high amount of ambient noise, as well as in some low spatial frequency regions (due to the influence of the contrast transfer function (CTF) of the electron microscope). In single-particle reconstruction, a satisfactory level of the SSNR in the 3D reconstruction is achieved by including a large number of 2D projections (tens to hundreds of thousands) that are averaged during the reconstruction process. Except for rare cases (Boisset et al., 1998), the angular distribution of projections is not an issue, as the large number of molecules and the randomness of their orientations on the support grid all but guarantee uniform coverage of angular space. The concern is whether the number of projections per angular direction is sufficient to yield the desired SSNR or whether the angular distribution of projections is such that the oversampling of the 3D Fourier space achieved during the reconstruction process will yield the desired SSNR.

Spherical aberration correction in nonlinear microscopy and optical ablation using a transparent deformable membrane

Abstract: We describe the design and utilization of a deformable membrane to minimize the negative spherical aberration that occurs when a standard water-dipping objective is used to focus within a higher-index sample. In connection with two-photon laser scanning microscopy, we demonstrate twofold improved axial resolution of structures as deep as 1mm in gels and brain tissue. In conjunction with plasma-mediated ablation, we demonstrate enhanced production of optical damage deep within a glass substrate. The present method provides a simple and inexpensive correction for a limited yet important class of optical aberrations.

Aberration coefficients of multi-element cylindrical electrostatic lens systems for charged particle beam applications

Abstract: In order to analyze the imaging properties of an electrostatic lens system, it is necessary to know how various sources of aberration combine to increase the size of final image or spot. In this paper, we investigated the spherical and chromatic aberration coefficients of multi-element electrostatic lens systems as a function of the lens voltages and magnification, using the electron ray tracing simulation programs S imion and L ensys . These programs can be used to obtain electron optical aberration integrals which involve the axial potential distribution and its derivative, and two independent trajectories and their derivatives for the determination of the third- or fifth-order aberration coefficients of multi-element lenses. Optical simulation of the intensity distribution has quantitatively shown that the aberration in the crossover image causes an electron beam blur and a positioning error on the focus spot. If a high positive voltage with respect to the first element's potential is applied to the lens elements, the aberrations as well as the minimum beam divergence can be reduced. The reason, obtained from numerical simulation, is that a positive voltage increases the electron velocity, shortening the electron drift time across the region with aberrant field.

Measurement of contrast transfer function in super-resolution microscopy using two-color fluorescence dip spectroscopy.

Abstract: The contrast transfer function (CTF) of super-resolution microscopy was quantitatively investigated using a fluorescent scale. The scale has minute fluorescent line patterns, finer than 100 nm, and is suitable for measuring CTF in super-resolution microscopy. The measured CTF shows that super-resolution microscopy can indeed improve the optical properties of fluorescent images and enable us to observe a structure with the spatial resolution overcoming the diffraction limit. From the CTF, it has been found that super-resolution microcopy can resolve a 100 nm line-and-space pattern and provides a contrast of 10%. The CTF corresponds to a PSF with a full-width at half-maximum (FWHM) of 130 nm. An evaluation using a 100 nmΦ fluorescent bead consistently supports the results given by the CTF for super-resolution microscopy.

Effect of a Physical Phase Plate on Contrast Transfer in an Aberration-Corrected Transmission Electron Microscope

Abstract: Extended abstract of a paper presented at Microscopy and Microanalysis 2007 in Ft. Lauderdale, Florida, USA, August 5 – August 9, 2007

Method of aberration correction and electron beam system

Abstract: There is disclosed an electron beam system in which the third-order aberration S 3 with two-fold symmetry is corrected. If a C s corrector (17) is operated, parasitic aberration S 3 (third-order aberration S 3 with two-fold symmetry) is produced. A corrective third-order aberration S 3 ' with two-fold symmetry that cancels out the parasitic aberration S 3 is produced within a multipole element (3,7) to correct the parasitic aberration S 3 . The electron beam (EB) is tilted relative to the optical axis (O) within the multipole element (3 or 7). The corrective third-order aberration S 3 ' with two-fold symmetry is introduced in each electron forming the tilted electron beam.

Correction method of image aberration of electron optical system

Abstract: PROBLEM TO BE SOLVED: To provide a method of removing the image aberration of the axis of an electron optical system, in which the image aberration of a first, second, third, and n-th dimensional order axis are removed, and a method of removing the image aberration of the electron optical system provided with a hexapole field. SOLUTION: The image aberration of an axis is removed by shifting or inclining a beam path using the aberration α and γ of the higher order image of the outside of an axis, wherein α n is the image aberrations on the axis of the electron optical system. The first and second order image aberrations in the electron optical system provided with the hexapole field are removed by superimposing a quadrupole field or the hexapole field on the hexapole field. COPYRIGHT: (C)2008,JPO&INPIT

Lens system for scanning device

Abstract: A lens system includes a lens (18) and a non-periodic phase structure (16). A temperature-dependence of the spherical aberration of the lens is compensated by a temperature dependence of the spherical aberration of the non-periodic phase structure. A wavelength-dependence of the defocus of the lens is compensated by a wavelength- dependence of the defocus of the non-periodic phase structure. A wavelength-dependence of the spherical aberration of the non-periodic phase structure is compensated by a wavelength- dependence of the spherical aberration of the lens.

Method for measuring information transfer limit in transmission electron microscope, and transmission electron microscope using the same

Abstract: A crystal thin film is adopted as a specimen for measurement. A change in the contrast of crystal lattice fringes is measured under a condition that a diffracted wave and other wave are caused to'interfere with each other. Thus, an information transfer limit of a transmission electron microscope can be measured quantitatively. Since the measurement is performed with a condition for interference restricted, the information transfer limit of the transmission electron microscope can be quantitatively assessed.

Quantitative evaluation of phase retrieval algorithms in propagation based phase tomography

Abstract: Phase contrast provides new possibilities in X-ray imaging, offering up to 1000 times higher sensitivity than standard absorption contrast. In propagation based phase contrast imaging, a quantitative relationship exists between intensity in the image plane and the phase shift induced by the object. Inversion of this relationship is called phase retrieval. Used as input to a 3D tomographic reconstruction algorithm this gives a reconstruction of the refractive index. Several methods for phase retrieval have been described, but few quantitative studies have been performed. In this paper we describe three phase retrieval methods, respectively based on the transport of intensity equation (TIE), contrast transfer function (CTF) and a mixed approach recently developed at the ESRF. The methods are evaluated using simulated and experimental data in the case of mixed absorption and phase objects. Using the TIE on simulated data we obtain a reconstruction with a mean error of 10%, but fail to achieve a qualitatively acceptable reconstruction of experimental data. The CTF approach yields qualitative reconstructions both using simulated and experimental data. Using the mixed approach, we obtain reconstructions with close correspondence to expected values with an average errors of 3.8% for the simulated and 5.9% for the experimental data

The Contrast Transfer Function of the SEM

Abstract: Extended abstract of a paper presented at Microscopy and Microanalysis 2007 in Ft. Lauderdale, Florida, USA, August 5 – August 9, 2007

Contrast Transfer Function Design by an Electrostatic Phase Plate

Abstract: Extended abstract of a paper presented at Microscopy and Microanalysis 2007 in Ft. Lauderdale, Florida, USA, August 5 – August 9, 2007

MTF Measuring Equipment of Optical System for LCD Substrate Inspection

Abstract: We developed the equipment to measure the MTF(modulation transfer function) of an optical system for automatically inspecting the surface condition of an LCD substrate. We have made an object generator with USAF(United States Air Force) targets of three bar patterns and an integrating sphere, and an image analyzer with a 2 dimensional CCD(charge coupled device) and a relay lens. The MTF of the lens under test was obtained by correcting the measured CTF(contrast transfer function) which is the ratio of the contrast in the image of the USAF target to the contrast in the object. We have measured an optical system of F/13.65 (2.6x), the MTF are 30.6 % tangential plane and 26.1 % sagittal plane at 62.5 1p/mm.

Spherical aberration correction apparatus and spherical aberration correction method

Abstract: PROBLEM TO BE SOLVED: To reduce the delay of information recording/reproducing start in an optical disk. SOLUTION: The spherical aberration correction apparatus includes a pickup 3 for applying a laser light to an optical disk 1 via an objective lens 15, a photodetector 17 for detecting the laser light incident through the objective lens 15 as a reflected light from the optical disk 1, a liquid crystal panel 14 for correcting a spherical aberration of the objective lens 15 with respect to the laser light, a flash-ROM 18 for storing beforehand an optimum relationship between a defocus position and a spherical aberration for various thicknesses of the optical disk 1, and a control unit 5 for measuring a thickness of the optical disk by applying a laser light to detect a reflected light from the optical disk 1, controlling the liquid crystal panel 14 to correct the spherical aberration corresponding to the defocus position of the relationship stored in the flash-ROM 18 with respect to the measured thickness of the optical disk 1. COPYRIGHT: (C)2009,JPO&INPIT

Spherical aberration correction moderating type lens, spherical aberration correction lens system, electron spectroscopy device, and optical electron microscope

Abstract: A spherical aberration correction decelerating lens corrects a spherical aberration occurring in an electron beam or an ion beam (hereinafter, referred to as "beam") emitted from a predetermined object plane position with a certain divergence angle, and said spherical aberration correction decelerating lens comprises at least two electrodes, each of which is constituted of a surface of a solid of revolution whose central axis coincides with an optical axis and each of which receives an intentionally set voltage applied by an external power supply, wherein at least one of the electrodes includes one or more meshes (M) which has a concaved shape opposite to an object plane (P0) and which is constituted of a surface of a solid of revolution so that a central axis of the concaved shape coincides with the optical axis, and a voltage applied to each of the electrodes causes the beam to be decelerated and causes formation of a decelerating convergence field for correcting the spherical aberration occurring in the beam. This makes it possible to provide a spherical aberration correction decelerating lens which converges a beam, emitted from the sample and having high energy and a large divergence angle, onto an image plane.

Influence of spherical aberration on beam parameters in design of laser optical focusing systems

Abstract: Using the second-order-moment and entropy-based definitions of the beam width,changes of the beam parameters including beam width,far-field divergence angle and beam quality factor of flat-topped beams passing through a spherically aberrated lens are studied.It is shown that the spherical aberration affects the beam parameters in the image space.The relative errors of the beam width and far-field divergence angle introduced by the spherical aberration increase with increasing spherical aberration coefficient and decreasing beam order.The spherical aberration results in an increase of the beam quality factor of flat-topped beams.The relative errors of the waist width at the real focal plane depend on the sign of the spherical aberration coefficient,whereas the relative errors of the beam width at the geometrical focal plane are independent of the sign of spherical aberration coefficient.

Investigation of image properties in super-resolution microscopy using two-color fluorescence dip spectroscopy

Abstract: We quantitatively investigated image properties in super-resolution microscopy using two-color fluorescence dip spectroscopy. To evaluate the properties, the point spread function (PSF) and contrast transfer function (CTF) were measured using a fluorescent scale together with a fluorescent bead. From the CTF, it has been found that visible light can resolve a 100 nm line-and-space pattern by microcopy, and provide a contrast of 10%. The CTF corresponds to a PSF with a FWHM of 130 nm. The value is two times finer than the diffraction limit size. An evaluation using a 100 nm Φ fluorescent bead consistently supports the result given by the CTF for super-resolution microscopy. The measured CTF shows that super-resolution microscopy can indeed improve the optical properties of fluorescent images and enable us to observe a structure with a spatial resolution overcoming the diffraction limit.

Measurement of Spherical Aberration Coefficient of the Objective Lens in KBSI-HVEM

Abstract: Coefficient of spherical aberration of the objective lens in the KBSI -HVEM was evaluated by diffractogram method. Instrumental resolution was also discussed with this method. In order to improve the accuracy, digital processing and graphical curve fitting for intensity profile of diffractogram were employed. Experimental concerns where the optimal procedure of the measurement can be accomplished for this study were discussed. The spherical aberration coefficient (C s) was estimated to be 2.628±0.04 mm from this study, which was almost coincident with the value of the manufacture’s suggestion (Cs=2.65 mm).

Spherical aberration correction of Gaussian beam

Abstract: The relationship between the Strehl ratio and the standard deviation of the wave front aberration of a Gaussian beam is derived from the diffraction integral in the presence of aberrations. Let it be required to develop the spherical aberration of a Gaussian beam into an aberration polynomial. For the maximum value of the Strehl ratio, a set of linear equations is obtained. The optimum configuration of the balanced spherical aberration is obtained from the solution of this set of linear equations. The coefficients of the spherical aberration of a Gaussian beam for the optimum design are illustrated in terms of tables. A comparison is made between the Strehl ratio of the corrected spherical aberration of the Gaussian beam using the optimum design of the uniform beam for the minimum RMS wave front aberration and those for the minimum P-V wave front aberration. The Strehl ratio of the configuration using the optimum design of the uniform beam changes slightly. It turns out that the spherical aberration of the Gaussian beam can be balanced with the optimum configuration of the uniform beam. Finally, the correction of the spherical aberration of the Gaussian beam is illustrated with an example.

Spherical aberration cancellation in a polarized photon-pairs confocal laser scanning microscope

Abstract: Refractive-index mismatch in conventional confocal microscopy produces severe degradation on axial resolution of sectioning image because the spherical aberration is generated in specimen. In this study, we propose a polarized photon-pairs confocal laser scanning microscope (PCLSM) in which a two-frequency linear polarized photon-pairs (LPPPs) laser beam is produced. The common-path propagation of LPPPs integrated with optical heterodyne technique not only can reduce the spherical aberration but also decreases scattering effect in specimen at same time. Therefore, the better axial and lateral resolutions of the sectioning image are produced simultaneously. In the experiment, a verification and comparison between PCLSM and conventional confocal laser scanning microscope (CLSM) on the ability of cancellation of spherical aberration induced by cover glass are demonstrated experimentally. Finally, the ability of PCLSM which can decrease the spherical aberration based on the common-path propagation of LPPPs associated with polarization gating, spatial coherence gating and spatial filtering gating is discussed.

Electron tomography of macromolecular assemblies

Abstract: Electron tomography is a method for three-dimensional reconstruction of a specimen, based on its electron microscopical projections which are produced by tilting the specimen in the microscope about a fixed axis. After determining a common coordinate frame, a tomogram is computed by weighted backprojection. Higher resolution can be obtained by applying a contrast transfer function (CTF) correction to the projections. The tomographic data is further analyzed by extracting structural motifs from the raw tomograms, by selective alignment, multivariate statistical analysis, classification, and class-averaging, resulting in an increased signal-to-noise ratio and substantial data reduction. The volumetric data analysis facilitates the separation of a heterogeneous population of motifs into its constituents, and the visualization of the motifs in the raw tomograms by reassembly, replacing low signal-to-noise instances with higher signal-to-noise representations