Topic
Contrast transfer function
About: Contrast transfer function is a research topic. Over the lifetime, 934 publications have been published within this topic receiving 26533 citations.
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28 May 2003
TL;DR: In this paper, the Wigner distribution of a laser from intensity profiles obtained by moving slit technology was determined experimentally from a plan-convex collimating lens orientated "the wrong way." The magnitude of the aberration can be influenced by the beam diameter at the lens.
Abstract: We determine the Wigner distribution of a laser experimentally from intensity profiles obtained by moving slit technology. In order to find out whether the phase calculated from a measured Wigner distribution can be trusted, we add a known spherical aberration to a Helium Noen laser by a plan-convex collimating lens orientated "the wrong way." The magnitude of the aberration can be influenced by the beam diameter at the lens. The M2-values calculated from the Wigner distribution of the aberrated beam at different levels of aberration is in agreement with theory. The coefficient of spherical aberration obtained from the measurement agrees with the one predicted by aberration theory if the impact of the aberration on the beam profiles is large enough (M2 > 1.2). The Wigner distribution of a tapered semiconductor laser is also examined. The measured phase at the semiconductor facet is aberrated. The aberration however can not be identified to origin from exit of the beam from high index semiconductor to air through a planar interface.© (2003) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
TL;DR: The analytical form of the intrinsic aberration coefficients for spherical plane-symmetric optical systems expressed as a function of first-order system parameters and the paraxial chief and marginal ray angles and heights was presented in this paper .
Abstract: This paper presents the analytical form of the intrinsic aberration coefficients for spherical plane-symmetric optical systems expressed as a function of first-order system parameters and the paraxial chief and marginal ray angles and heights. The derived aberration coefficients are in the third and fourth groups with the multiplication of two or three vector products of pupil and field vectors.
TL;DR: In this article, the influence of defects and impurities in 2-dimensional materials on experimental electron energy loss spectroscopy (EELS) maps is discussed, and the underlying contrast mechanisms can be explained using a combination of density functional theory (DFT) and dynamical electron scattering theory.
Abstract: Aberration correction of electron optics has provided not only higher resolution, but also higher contrast. This is particularly true for scanning transmission electron microscopes (STEMs) operating at lower accelerating voltages, which has allowed atomic resolution of 2-dimensional materials using both annular dark field (ADF) and electron energy loss spectroscopy (EELS) based on core-loss excitations [1,2]. It has until recently been assumed that atomic resolution images based on low-loss or valance EELS (VEELS) would not be possible, due to the assumed delocalization of the inelastic interaction involved. This has recently been shown not to be the case, with atomic resolution VEELS maps obtained from graphene using aberration corrected STEM and explained using first principles theory [3]. In this presentation we discuss the influence of defects and impurities in 2-dimensional materials on experimental VEELS maps, and how the underlying contrast mechanisms can be explained using a combination of density functional theory (DFT) and dynamical electron scattering theory [4].
05 Mar 2021
TL;DR: In this paper, the distortion function attenuates the frequency components in the pass band resulting in a blurry phase image and an optimal wiener filter is employed to deconvolve the distortion functions.
Abstract: Transport of Intensity Equation (TIE) is a powerful computational tool for quantitative phase imaging using intensity only measurement. However, one drawback of TIE is that it does not include any parameters of the imaging system in the equation. To account for the effect of the imaging system on the retrieved phase, TIE is reformulated using Contrast Transfer Function (CTF) to analytically derive the distortion functions present in TIE. The distortion function attenuates the frequency components in the pass band resulting in a blurry phase image. For image restoration, signal parameters are estimated by minimizing a cost function for power spectrum and an optimal wiener filter is employed to deconvolve the distortion function. The proposed method is experimentally demonstrated through a visible enhancement in the phase images of human cheek cells obtained using a bright field microscope.
TL;DR: In this paper, a new objective lens design for an electron beam probe was reported, which was a sharp (50 meV) secondary electron transfer function with low aberration coefficients for the primary beam.