Showing papers on "Contrast transfer function published in 1994"
TL;DR: In this article, the scalar three-dimensional optical transfer function without using the paraxial approximation was derived for a partially coherent system with equal condenser and objective apertures and the coherent transfer function for a confocal transmission system.
Abstract: The scalar three-dimensional optical transfer function is derived without using the paraxial approximation. The weak-object transfer function for a partially coherent system with equal condenser and objective apertures and the coherent transfer function for a confocal transmission system are of identical form. The coherent transfer function of a confocal reflection system is also derived. Both uniform angular illumination and systems obeying the sine condition are considered. In all cases the transfer functions can be expressed analytically.
112 citations
TL;DR: It is shown both theoretically and experimentally that the aberrated axial response can be improved by slightly reducing the lens aperture size.
Abstract: The influence of spherical aberration on axial imaging of confocal reflection microscopy is investigated. In particular, the effects of lens aperture size and of the first three orders of spherical aberration are inspected. It is shown both theoretically and experimentally that the aberrated axial response can be improved by slightly reducing the lens aperture size. The experimental results concerning the effect of the tube length on the axial response and the aberration compensation are also given.
76 citations
TL;DR: In this article, the authors investigated the three-dimensional optical transfer function for both circular and annular lenses in the presence of combined spherical aberration and defocus, with attention centered on its phase.
Abstract: The three-dimensional optical transfer function for both circular and annular lenses in the presence of combined spherical aberration and defocus is investigated, with attention centered on its phase. Results show that it is possible to reduce the phase variation of the optical transfer function optimally for a circular lens by introducing defocus according to the condition of least confusion. In the appendixes it is shown how to calculate the in-focus and on-axis transfer function from the three-dimensional optical transfer function.
27 citations
TL;DR: In this paper, it was shown that the focal shift of a Gaussian laser beam can be offset with the use of the spherical aberration of a focusing lens, which is applicable to a low Fresnel number focusing system.
22 citations
TL;DR: In this paper, the validity of weak-phase object approximation in amorphous thin films is resolution dependent, and the appearance of diffractograms from far out-of-focus to measure the information-limit resolution, and other optical parameters.
22 citations
TL;DR: The effects of defocus and primary spherical aberration on the images of a straight edge in a confocal microscope are investigated and one can improve the quality of the edge images, particularly the sharpness, by slightly reducing the aperture size of the objective and the collection lenses.
Abstract: The effects of defocus and primary spherical aberration on the images of a straight edge in a confocal microscope are investigated. When the aberrations are small, the sharpness of the edge image may be enhanced. But the images are degraded if the aberrations become strong in the system. In the latter case, one can improve the quality of the edge images, particularly the sharpness, by slightly reducing the aperture size of the objective and the collection lenses. This result is qualitatively verified by experimental results.
17 citations
TL;DR: In this article, an approximate phase object is assumed to be an amorphous carbon film and a symmetrical aberration function parametrized only by a spherical aberration coefficient and a defocus value.
14 citations
TL;DR: Ishizuka et al. as mentioned in this paper corrected the aberration of structure images significantly beyond the Scherzer limit using the holography technique, which can be applied to a specimen commonly used for high-resolution electron microscopy, even when a simple phase object approximation breaks down.
12 citations
17 May 1994
TL;DR: In this paper, the classification and treatment of scan-induced image degradation is presented. But the authors do not consider the effect of lens aberrations, mechanical vibrations as well as synchronization errors of the stages.
Abstract: Step and scan projection printers overcome the most stringent restriction of step and repeat cameras: the trade off between the resolving power of the lithographic lens and its image field. In a scanning projection printer the reticle and wafer both have to be moved with a constant velocity, keeping their speed ratio equal to the reduction of the lens. The length of the circuit is now reticle limited. An additional extension consists in stitching several lanes together in order to lengthen the dimension perpendicular to the scan direction. However, lens aberrations, mechanical vibrations as well as synchronization errors of the stages, deteriorate the image transfer. The aim of this article is the classification and treatment of these scan- induced deteriorations. So-called contrast transfer curves are calculated offering the possibility of gaining quantitative values of the disturbance amplitudes for permissible contrast drops. Additionally, exposure-defocus (ED) trees are constructed as an evaluation criterion of the scan-induced image degradation.
8 citations
TL;DR: In this paper, a method for quantifying the information contained in high-resolution electron micrographs by the measurement of the intensity of reflections in diffractograms is presented, where the imaging parameters are determined simultaneously with the amplitudes and phases of the Fourier components of the exit-surface wave function.
8 citations
TL;DR: Application of this newly developed aberration-correction method to high-resolution off-axis electron holograms of fine gold particles is presented and the phase distribution of the corrected object wave is visualized by the Zernike phase-contrast method.
Abstract: One can correct spherical aberration in a transmission electron microscope by using a newly developed aberration-correction method involving off-axis electron holography. In this method, a liquid-crystal spatial-light modulator (LC SLM) is employed during the holographic reconstruction step to compensate for spherical aberration. Application of this method to high-resolution off-axis electron holograms of fine gold particles is presented. The phase distribution of the corrected object wave is visualized by the Zernike phase-contrast method carried out with the same LC SLM.
Journal Article•
TL;DR: In this paper, the theoretical basis of defocus-modulation image processing (DMIP) for correcting spherical aberration in transmission electron microscopy is clarified, and a novel approach of practical use for verification of the just-focus position and aberration function by DMIP is also proposed.
TL;DR: A review of electron optical bench literature is presented in this article, and the designs of two optical benches used by the authors are described, one is a branched system designed for several purposes: to study correction of spherical and chromatic aberration with an electron mirror, and to gain experience with low energy electron microscopy (LEEM) optics.
Abstract: A review of electron optical bench literature is presented, and the designs of two optical benches used by the authors are described. One bench was designed for testing individual electrostatic electron lenses and in‐line optical systems, for example, emission electron microscopes and transmission electron microscopes. It has been in operation for many years. The second electron optical bench is new. It is a branched system designed for several purposes: to study correction of spherical and chromatic aberration with an electron mirror, and to gain experience with low energy electron microscopy (LEEM) optics. The alignment of the electron optical support structure is independent of the vacuum housing, and the bench is designed to be operated either horizontally or vertically. As a demonstration of the performance of the new bench in the horizontal mode, a test pattern on a silicon surface was imaged with LEEM optics.
TL;DR: A method that approximates a diffraction formula to the Fourier integral formula by the application of a coordinate transformation is proposed, and it is proved to be a superior and more accurate approximation when it is applied to focusing systems under a nonsine condition.
Abstract: A method that approximates a diffraction formula to the Fourier integral formula by the application of a coordinate transformation is proposed, and it is proved to be a superior and more accurate approximation when it is applied to focusing systems under a nonsine condition. Based on this approximation, the condition that gives the diffraction focus position is derived by the application of two methods. The first is applicable to rotationally symmetrical aberrations such as spherical aberration, and the second is a more general method that utilizes the standard deviation of a wave aberration. These methods are actually applied to a grating lens as a way to study both chromatic aberration characteristics and oblique incidence characteristics.
TL;DR: In this paper, chemical lattice imaging is applied to AlGa1−xAs structures and reveals differences in the abruptness of GaAs on AlxGa1+xAs and AlgaAs on GaAs interfaces.
Abstract: Chemical information on a near-atomic scale may be obtained from high-resolution transmission electron microscope (HREM) images. This requires first a distinct contrast difference in the adjacent semiconductor materials in a particular projection direction for a wide range of objective lens defoci and specimen thicknesses for the given microscope parameters (acceleration voltage, spherical aberration constant). Second, the image must contain Fourier components which behave almost linear with layer composition. The contrast formation in the systems Al/GaAs and Si/Ge, where such conditions may be found and which are representative for amplitude and phase contrast respectively, is discussed. The method of chemical lattice imaging is applied to AlxGa1−xAs structures and reveals differences in the abruptness of GaAs on AlxGa1−xAs and AlxGa1−xAs on GaAs interfaces. Selected area diffraction systems with high accuracy.
01 Jan 1994
TL;DR: In this paper, the authors discuss the principle of bright-field imaging and a drawback of the bright field technique and present the graphical presentation of bright field hollow-cone transfer functions at optimum focus for various values of Γ 2.
Abstract: Publisher Summary
This chapter discusses the principle of bright-field imaging and a drawback of the bright-field technique. It reviews the bright-field image formation in terms of transfer functions. The chapter explains the phase contrast and amplitude contrast transfer function and discusses the spectral distributions of the illumination. It further focuses on the imaging of weakly scattering specimens in axial bright-field imaging conditions and presents the graphical presentation of bright-field hollow-cone transfer functions at optimum focus for various values of Γ2. The linear transfer theory depends essentially on the assumption that the unscattered beam is considerably stronger than the scattered beam, but this may well not be true for crystalline specimens, where the electrons are concentrated in spots in the back-focal plane of the objective.
31 May 1994
TL;DR: In this article, the authors investigated the feasibility of using an adaptive mirror for in-orbit aberration corrections and showed that the mirror shape can be adjusted in an iterative fashion until the best image is obtained.
Abstract: We investigate the feasibility of using an adaptive mirror for in-orbit aberration corrections. The advantage of an in-situ aberration correction of optical components in the space environment is that the mirror shape can be adjusted in an iterative fashion until the best image is obtained. Using the actuator spacing, corresponding to one-half the Nyquist frequency, the Strehl ratio of the corrected wavefront improves to 0.95 when the mirror is fabricated with 6.5 waves of spherical aberration. The Strehl ratio is decreased to 0.86 when the number of actuators is reduced by a factor of 4, in a 2D adaptive optics model.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
TL;DR: By averaging phase correlations between scattered electrons, a high angle detector in the scanning transmission electron microscope (STEM) can provide an incoherent, Z-contrast image at atomic resolution as discussed by the authors.
Abstract: By averaging phase correlations between scattered electrons a high angle detector in the scanning transmission electron microscope (STEM) can provide an incoherent, Z-contrast image at atomic resolution. Phase coherence is effectively destroyed through a combination of detector geometry (transverse incoherence) and phonon scattering (longitudinal incoherence). Besides having a higher intrinsic resolution, incoherent imaging offers the possibility of robust reconstruction to higher resolutions, provided that some lower frequency information is present in the image. This should have value for complex materials and regions of complex atomic arrangements such as grain boundaries. Direct resolution of the GaAs sublattice with a 300kV is demonstrated.
23 Mar 1994
TL;DR: In this paper, the contrast transfer function (CTF) for each individual stage in the voltage imaging process is derived, which is a function of the EO material, the image forming optics, the CCD resolution and electronic filter bandwidth, and the image processor resolution and filter bandwidth.
Abstract: The spatial resolution of the Voltage ImagingTM technology is defined as the smallest pixel pitch that can be measured for a certain voltage accuracy. It is a function of the EO material, the image forming optics, the CCD resolution and electronic filter bandwidth, and the image processor resolution and filter bandwidth. This paper starts from a square wave input signal with 100% modulation on the LCD panel. The contrast transfer function (CTF) for each individual stage in the voltage imaging process is derived. They include the EO material, the objective lens and imaging lens, the CCD camera spatial sampling, the CCD camera electronics filtering, and the image processor sampling and filtering. Simulated data is presented.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
TL;DR: In this article, a more complete form of contrast transfer theory was derived using a partial coherency approach for both electron holography and conventional high resolution electron microscopy, which is used in this paper.