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.

Image resolution and image contrast in the electron microscope. I. Elastic scattering and coherent illumination

Abstract: The present work evaluates the effect of lens aberrations on image resolution and image contrast in the transmission electron microscope for the elastic component of the electron beam; coherent illumination of the specimen is assumed. The effects of lens aberrations on the image resolution are evaluated in terms of a resolution function in preference to the use of the transfer function. Although no precise figures can be given for image resolution, it is found that the condition for maximum contrast corresponds to the best resolution in the image. The fundamental limit in resolution, due to diffraction at the objective aperture, should be avoided by increasing the objective aperture size with a subsequent correction for the increased lens aberrations. For coherent illumination these corrections can, in general, only be made in bright field microscopy and not in dark field microscopy.

Spherical Aberration of Compound Magnetic Lenses

Abstract: A reduction of the spherical aberration of strong electron lenses can be achieved by a strong lens as a virtual image former and by a transformation of the image in a real one by means of one or more weak lenses. Calculations are carried out for bell‐shaped magnetic fields of the axial field distribution H(z)=H01+(z/a)2, and numerical values of the achieved reduction of the aberration are given for different lens strength, magnification, and image distance of the compound system.

Correction of spherical and azimuthal aberrations in radially polarized beams from strongly pumped laser rods

Abstract: Spherical aberration of heavily pumped Nd:YAG rods was corrected by use of spherical relay optics selected to add conjugate amounts of aberration. Wavefront measurements showed elimination of spherical aberration. Correction of spherical aberration allowed 250 W of power to be generated in a radially polarized, birefringence-free oscillator (60% more power than without correction). Scale-up of wavefront maintenance was demonstrated in a two-rod amplifier module (6.3 kW electrical pump power). Radial polarization and spherical aberration correction together eliminated the main aberrations in uniformly pumped rod-based lasers. Rotating adjacent pump chambers substantially reduced the multifold aberrations induced by nonuniformity of the azimuthal pumps. ΔM2 in the radially polarized beam was 0.3 and 1.4 with and without aberration correction, respectively, in each two-pump chamber module. Analysis predicts further improvements when higher-order aberration correction is applied.