Showing papers on "Contrast transfer function published in 1993"

Impact of chromatic and spherical aberration on the focusing of ultrashort light pulses by lenses.

Abstract: Focusing of ultrashort light pulses with single lenses is analyzed by taking into account the unavoidable interplay between chromatic and spherical aberration simultaneously for the first time to our knowledge. The spatial intensity distribution is mainly affected by spherical aberration, whereas the temporal distribution is determined by both aberrations. The impact on second-harmonic generation for femtosecond pulse measurements is discussed. For example, the presence of spherical aberration allows one to record the correct autocorrelation of a 10-fs pulse even if chromatic aberration alone would cause a half-width of the autocorrelation function of 40 fs.

An Analytical Solution of Vector Diffraction for Focusing Optical Systems with Seidel Aberrations: I. Spherical Aberration, Curvature of Field, and Distortion

Abstract: In this paper, a method developed by the author is used to study the image formation in various aplanatic systems with Seidel (fourth-order) aberrations We study the spherical aberration, the distortion aberration and the curvature of field aberration Just as in the case of scalar diffraction theory, it is shown that the distortion produces a shifted intensity pattern while in contrast with the scalar theory it is shown that the curvature of the field aberration produces a different intensity distribution We also provide expressions for the location of the diffraction foci and calculate the Strehl intensity We find that for the case of spherical aberration, the Strehl intensity increases with the increase in the numerical aperture whereas for the case of curvature of field aberration the Strehl intensity decreases with the increase in the numerical aperture For distortion aberration the Strehl intensity is same as the Gaussian intensity The computations are carried out for a focusing lens

Method for accurate optical alignment using diffraction rings from lenses with spherical aberration.

Abstract: A useful alignment method is presented that exploits the closely spaced concentric fringes that form in the longitudinal spherical aberration region of positive spherical lenses imaging a point source. To align one or more elements to a common axis, spherical lenses are attached precisely to the elements and the resulting diffraction rings are made to coincide. We modeled the spherical aberration of the lenses by calculating the diffraction patterns of converging plane waves passing through concentric narrow annular apertures. The validity of the model is supported by experimental data and is determined to be accurate for a prototype penumbral imaging alignment system developed at Lawrence Livermore National Laboratory.

Spherical aberration, intraocular lens power, and image quality

Abstract: Spherical aberration for intraocular lenses is calculated based on surface contributions. The impact on image quality can be determined using a defined pupil function. Relationship between wavefront aberration and displacement of the best focal plane is discussed. The impact on ANSI Z80.7 power labelling is computed and found to be as great as 0.9 Diopters for standard lens types from the combination of media conversion error and spherical aberration. A pupil function is defined for solution of the Fresnel diffraction integral, in the Fraunhofer approximation, and is used to compute strehl ratio and modulation transfer function for symmetrical biconvex, convex plano and meniscus lenses in standard atmosphere and in situ. Results in air indicate best optical performance for convex plano lenses due to minimization of spherical aberration. In situ, all lenses analyzed performed approximately equally well. Use of this calculation technique for refractive bifocal IOL performance prediction is discussed.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Partially coherent image reconstruction

Abstract: Features of spatial filtering of partially coherent images are investigated. A radiooptical analogy method for analysis of optical system operation is used. Analytic expression of optical transfer function for arbitrary coherence of illumination field, for arbitrary aperture factors and for arbitrary defocusing parameter is deduced and investigated by numerical methods. Efficiency of spatial filtering of partially coherent images has been showed by laboratory experimental system using illumination source with variable coherence. An original method with two synchronously tunable moire patterns has been used for optical transfer function measurements. Investigation results are interpreted from the point of view of solving inverse problem.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Aberration correction by electron holography using a liquid crystal spatial-light modulator

Abstract: Electron holography has a potential to overcome the resolution limitation of transmission electron microscopes imposed by a spherical aberration of an electron objective lens. This paper describes a new optical system a liquid-crystal spatial-light modulator (LC-SLM) to correct a spherical aberration from an off-axis electron hologram. The effective refractive index of the liquid crystals changed by the applied electric field can flexibly compensate for a wave aberration. Some experimental results involving the correction of the spherical aberration in an off-axis image electron hologram are presented. Zernike phase contrast method is also realized by the LC-SLM to visualize the phase distribution of a corrected object wave.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Three-Dimensional Coherent Transfer Functions in Confocal Scanning Imaging

Abstract: We report on the analysis of the three-dimensional (3-D) image formation in a confocal microscope in terms of the concept of the 3-D coherent transfer function (CTF). The effects of the annular pupil function and spherical aberration on the 3-D CTF are investigated. The 3-D CTF for a new fibre-optical confocal system consisting of optical fibres for illumination and collection is described. We also discuss the significance of the 3-D CTF and, in particular, the relationship between the 3-D CTF and 2-D and 1-D imaging.