Showing papers by "Min Gu 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 three-dimensional transfer functions in order to understand image formation in the recently proposed 4Pi confocal microscope, and showed that the cutoff spatial frequency in the axial direction is larger than that in the transverse direction.
Abstract: We investigate three-dimensional transfer functions in order to understand image formation in the recently proposed 4Pi confocal microscope [ J. Opt. Soc. Am. A9, 2159 ( 1992);Opt. Commun.93, 277 ( 1992)]. Both nonfluorescence and fluorescence imaging methods are considered, and the effects of apodization functions are taken into account. It is shown that for a 4Pi confocal system of finite-sized aperture the cutoff spatial frequency in the axial direction is larger than that in the transverse direction; this behavior is opposite that of conventional confocal systems, explaining the observation of high axial resolution in 4Pi confocal systems. In addition, the three-dimensional optical transfer function for a conventional confocal fluorescence microscope of high aperture is presented.
41 citations
TL;DR: In this article, the axial image of a thick fluorescent layer is studied in a confocal microscope consisting of either circular or annular pupils, and it is shown that for a given detector of finite size, axial resolution in confocal fluorescence microscopy can be improved when an annular lens is used.
28 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: 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 paper, the effects of the detector size on the 3D weak-object transfer function (WOTF) for weakly scattering objects are studied in detail in terms of the WOTF.
Abstract: The concept of the transmission cross-coefficient (TCC) is used to describe three-dimensional (3D) imaging in transmission and reflection confocal scanning microscopes with a finite-sized detector. The effects of the detector size are studied in detail in terms of the 3D weak-object transfer functions (WOTFs) for weakly scattering objects. As is already known, 3D transmission imaging for an infinitely large detector and for a point detector are identical, whereas it is shown that between two limiting cases the behaviour is different, suggesting that axial phase information can be imaged. It is found that 3D reflection imaging for an infinitely large detector can be equivalent to 3D true confocal imaging using one annular and one circular pupil. The 3D WOTF in reflection reveals negative values which may reverse the contrast of an image at some spatial frequencies.
12 citations
TL;DR: In this article, it was shown that the 3D amplitude point spread function (APSF) under ultrashort light-pulse illumination neglects some factors, and a complete expression for the 3-D APSF for general cases was given.
Abstract: We show that the three-dimensional (3-D) amplitude point-spread function (APSF) under ultrashort light-pulse illumination reported by Kempe and Rudolph [ J. Opt. Soc. Am. A10, 240 ( 1993)] neglects some factors. A complete expression for the 3-D APSF for general cases is given.
9 citations
TL;DR: In this article, the role of the illumination system of the confocal microscope, and in particular the first pinhole, is discussed, and the effects of a finite sized source on the imaging performance, including the three-dimensional optical transfer function, are investigated.
Abstract: The role of the illumination system of the confocal microscope, and in particular the first pinhole, is discussed. The effects of a finite sized source on the imaging performance, including the three-dimensional optical transfer function, are investigated. Two forms of source are considered, either a coherent Gaussian beam of finite size or an incoherent disc of finite size. For a confocal microscope using optical fibres as source and detector, the optimum geometry is derived for maximizing signal strength.
9 citations
30 Sep 1994
TL;DR: In this paper, the way in which a reflection or transmission microscope image depends on the variations in complex refractive index in the object is considered, and a generalized form for the scattering potential for reflection imaging in the Born approximation is proposed.
Abstract: The way in which a reflection or transmission microscope image depends on the variations in complex refractive index in the object is considered. Reflection objects including rough surfaces and stratified media are discussed, and a generalized form for the scattering potential for reflection imaging in the Born approximation proposed. Reconstruction of the refractive index variation in a stratified medium is considered. Transmission imaging formation based on the Born and Rytov approximations is discussed. These properties are important for interpretation of the resulting images, and also as a basis for digital restoration methods.
6 citations