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.

Chromatic Confocal Electron Microscopy with a Finite Pinhole Size

Abstract: Scanning confocal electron microscopy (SCEM) is a new imaging mode in electron microscopy. Spherical aberration corrected electron microscope instruments fitted with two aberration correctors can be used in this mode which provides improved depth resolution and selectivity compared to optical sectioning in a conventional scanning transmission geometry. In this article, we consider the depth resolution and energy resolution in the confocal optical configuration for SCEM using inelastically scattered electrons with a finite pinhole size. We experimentally demonstrate energy-filtered optical sectioning in a double aberration-corrected instrument with uncorrected chromatic aberration without using a dedicated energy filter.

Microwave holographic remote sensing using a Fourier transform/spherical scanning technique

Abstract: Spherical scanning is a very convenient means of mapping a microwave aperture for a localized remote imaging system. Provided that the scan angle does not exceed the derived limits for tolerable spherical aberration, a Fourier microwave hologram, recorded on a spherical surface, yields clearly identifiable, computer-reconstructed images.

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.

Evaluation of scanning electron microscope resolution

Abstract: The evaluation of Scanning Electron Microscopes (SEM) resolution through Two Dimensions Fast Fourier Transform (2D FFT) image analysis is becoming a standard. We propose an improvement of these methods with a patented technique. This new image processing is designed to extract the transfer function of the SEM from the picture and then to realize the analysis of this function. A first algorithm extracts an 'ideal' image of the sample from the 'raw' image obtained on the equipment. Then a second algorithm extracts the SEM transfer function through a comparison between the two images ('ideal' and 'raw'). Finally a third algorithm modelizes the transfer function as a two dimensions Normal function and draws out the result. The representation of the transfer function of the SEM with a Normal function allows to define the shape of an Equivalent of the Electron Beam (EEB). This EEB represents the primary electron beam altered by the interactions with the sample and the losses in the acquisition loop. It is important to outline these alterations as they limit the sharpness of the images obtained from the tool. This way of doing lessens the influence of sample parameters on the final results and thus represent more precisely the SEM Transfer Function.

Model-based Reconstruction for Single Particle Cryo-Electron Microscopy

Abstract: Single particle cryo-electron microscopy is a vital tool for 3D characterization of protein structures. A typical workflow involves acquiring projection images of a collection of randomly oriented particles, picking and classifying individual particle projections by orientation, and finally using the individual particle projections to reconstruct a 3D map of the electron density profile. The reconstruction is challenging because of the low signal-to-noise ratio of the data, the unknown orientation of the particles, and the sparsity of data especially when dealing with flexible proteins where there may not be sufficient data corresponding to each class to obtain an accurate reconstruction using standard algorithms. In this paper we present a model-based image reconstruction technique that uses a regularized cost function to reconstruct the 3D density map by assuming known orientations for the particles. Our method casts the reconstruction as minimizing a cost function involving a novel forward model term that accounts for the contrast transfer function of the microscope, the orientation of the particles and the center of rotation offsets. We combine the forward model term with a regularizer that enforces desirable properties in the volume to be reconstructed. Using simulated data, we demonstrate how our method can significantly improve upon the typically used approach.