Boots – shoes – and leggings
Patent
1983-09-23
1986-01-28
Arnold, Bruce Y.
Boots, shoes, and leggings
364822, G03H 116
Patent
active
045667578
DESCRIPTION:
BRIEF SUMMARY
Technical Field
The present invention relates generally to analysis of the microstructure present in large transparent or semi-transparent volumes or over large object surface areas and, more particularly, to the performance of such analysis through the use of optical processing techniques.
BACKGROUND ART
As is well known in the art, an optical Fourier transformation can be performed on a subject by illuminating the subject with a coherent light source and using a lens to collect the reflected, and/or diffracted and/or transmitted light containing optical information corresponding to the subject. The lens will define a Fourier transform of the orignal subject information in a plane located one focal length away from the lens at its focus. With this process, subject information is redistributed in the Fourier transform plane to correspond to spatial frequency content. A second lens, located two focal lengths from the first, images the information onto a display screen, recording medium, or the like.
The optical information coming from the subject may be manipulated for the purpose of enhancing detail, removing unwanted subject information, isolating defects, or making precise topographic and optical path measurements. This is accomplished by blocking a portion of the subject information or changing its phase within the transform plane. These techniques are particularly useful where the subject consists of repetitive spatial frequency content such as is present in photomasks or wafers used in the production of microelectronic circuits, since the optical Fourier transform will consist of an array of regularly spaced points of light whose distance from the optical axis is proportional to the spatial frequency.
One example of such a technique is disclosed in U.S. Pat. No 4,000,949 issued Jan. 4, 1977 to Watkins. Using the basic processing scheme outlined above, a photomask is used as the subject. An optical spatial filter is placed within the Fourier transform plane for blocking all subject information other than that corresponding to nonperiodic defects in the mask. Since only defect information will pass through to the display screen, the number of defects and their locations can be determined.
It can be easily seen, however, that aberrations within the optical components of an optical processor, particularly within lenses focusing the subject information and/or the processed information, will be a significant detriment to use of the otpical processor with subjects having microscopic detail. On axis, for example, a focus error aberration can cause loss of spatial frequency information, as illustrated by way of example for a typical optical telescope system in FIG. 1.
A three-lens system 24 is shown, wherein lenses 1.sub.1 and 1.sub.2 are F/1.50, 50 mm diameter, 75 mm focal length lenses, and lens 1.sub.3 is an F/1.50, 150 mm diameter, 225 mm focal length lens. Assuming the sum of the spherical aberration from lenses 1.sub.2 and 1.sub.3 to be 2 mm, the focus of the rays 26 entering the system 24 is moved from a point 28 to a point 30, 77 mm away from lens 1.sub.1. This results in a smaller, F/1.54 collection angle at lens 1.sub.1.
Therefore, with a 225 mm focal length for lens 1.sub.3, which would give an F/4.5 collection angle for lens 1.sub.3 and the system 24 as a whole if lens 1.sub.1 collected F/1.50, the lens can only collect: ##EQU1##
Similarly, for 1 mm of special aberration, the focal point is moved to 76 mm away from lens 1.sub.1 and: ##EQU2## for the system 24.
To consider these effects directly, the optical transfer function (OTF) of the system may be looked to.
For a diffraction limited system: ##EQU3## where a (f.sub.x,f.sub.y) is the area of overlap of the pupil collecting spatial frequencies with the restricting pupil function. The OTF with aberrations for two pupils given by: ##EQU4## where W is the aberration function.
The Schwarz inequality, .ltoreq.(.intg..intg..vertline.X.vertline..sup.2 d.xi.d.eta.) (.intg..intg..vertline.Y.vertline..sup.2 d.xi.d.eta.) (f.sub.x,f.sub.y).sub.no abberra
REFERENCES:
patent: 3514176 (1970-05-01), Brooks et al.
patent: 4220928 (1980-09-01), Bloom et al.
Briones et al., "Holographic Microscopy", Applied Optics, vol. 17, No. 6, Mar. 15, 1978, pp. 944-950.
Toth et al., "Reconstruction of a Three-Dimensional Sample using Holographic Techniques", Applied Physics Letters, vol. 13, No. 1, pp. 7-9.
Knox, "Holographic Microscopy as a Technique for Recording Microscopic Subjects", Science, vol. 153, pp. 989-990, Aug. 26, 1966.
Fusek Richard L.
Harding Kevin G.
Harris James S.
Arnold Bruce Y.
University of Dayton
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