Showing papers on "Zone plate published in 1977"
TL;DR: It is shown that, although Abbe's sine law applies to zone plates but not to Fresnel lenses, both can yield single-element aplanats if formed on a curved surface.
Abstract: The generalization of zone plates and Fresnel lenses from the usual flat surfaces to curved surfaces is discussed. It is shown that, although Abbe's sine law applies to zone plates but not to Fresnel lenses, both can yield single-element aplanats if formed on a curved surface. Third-order aberration formulas are given.
43 citations
TL;DR: A Fresnel zone plate of variable size can be formed as a moiré pattern between a suitable pair of identical grids to monitor the straightness of a continuous linear motion.
Abstract: A Fresnel zone plate of variable size can be formed as a moire pattern between a suitable pair of identical grids. The focusing power may be varied over a considerable range by relative translation of the grids if their line sbapejs are determined by a combination of cubic and linear functions. Elliptical and hyperbolic patterns are also obtainable. If both grids ae constructed in phase reversal form, the irradiance in the diffraction image due to the zone plate is enhanced substantially. The device may then be used with photoelectric detection to monitor the straightness of a continuous linear motion. A possible application to field widening in interference spectroscopy is also suggested.
32 citations
TL;DR: In this article, a method for removing the wavefront error caused by an Optically recorded Fresnel zone plate for laser beam scanning is discussed, and the feasibility of the method is demonstrated.
Abstract: Optically recorded Fresnel zone plates have proper spatial frequency characteristics for use as a laser scanner. Such grating scanners can easily be made and can scan over large cone angles with, however, severe aberrations of the diffracted laser beam at large deflection angles. Optically recorded Fresnel zone plates for laser beam scanning are investigated, and their aberration properties are analyzed. A method for removing the wavefront error caused by this type of zone plate is discussed, and the feasibility of the method is demonstrated.
19 citations
Patent•
01 Dec 1977
TL;DR: In this article, a planar negative type of photographic film is patterned by exposure through a master transparent sheet of plastic on which star locations, zone plate lens, or lines representing geographical boundaries or other figures are drawn in opaque ink.
Abstract: A planetarium projector and the method of making the projector is described wherein a light source is surrounded by an opaque enclosure having transparent spots or lines. The enclosure is fabricated from originally planar sheets of photographic film. The enclosure is preferably cylindrical however it may assume other shapes such as conical or a rectangular parallelepiped. The planar sheets of negative type of photographic film are patterned by exposure through a master transparent sheet of plastic on which star locations, zone plate lens, or lines representing geographical boundaries or other figures are drawn in opaque ink.
11 citations
Patent•
10 Nov 1977
TL;DR: In this article, a screen and a Fresnel lens are arranged such that the Optically inactive surfaces of the Fresnel surface become approximately parallel with the advancing direction of projected rays entered through and refracted by the back surface of the lens.
Abstract: A screen means free from ghost image comprising a screen and Fresnel lens arranged so that its Fresnel surface faces the screen. The Fresnel lens is arranged that optically inactive surfaces of its Fresnel surface become approximately parallel with the advancing direction of projected rays entered through and refracted by the back surface of the Fresnel lens.
10 citations
01 Aug 1977
TL;DR: In this paper, a simple optical model was introduced to study the effects of base curvature and lens f-number on the solar concentration performance of idealized curved base line focusing Fresnel lenses.
Abstract: The solar concentration performance of idealized curved base line focusing Fresnel lenses is analyzed. A simple optical model was introduced to study the effects of base curvature and lens f-number. Thin lens ray tracing and the laws of reflection and refraction are used to develop expression for lens transmittance and image plane intensity profiles. The intensity distribution over the solar spectrum, lens dispersion effects, and absorption by the lens material are included in the analysis. Model capabilities include assessment of lens performance in the presence of small transverse tracking errors and the sensitivity of solar image characteristics to focusing.
5 citations
TL;DR: In typical experiments with narrow field objects, it is shown that the zone plate behaves like a diffraction-limited lens, the gain in resolution is noticeable as the wavelength decreases, the use of the third-order focus improves the resolution of the system, and under certain conditions the depth of field can be increased without loss of resolution.
Abstract: The feasibility of optical systems for short wavelength radiations ranging from the near uv to soft x rays is supported by theoretical and experimental arguments. The major problem of absorption of these radiations by materials has been overcome in the near and middle uv by using the lens properties of a Fresnel zone plate generated on a thin self-supporting film. In typical experiments with narrow field objects, it is shown that the zone plate behaves like a diffraction-limited lens, the gain in resolution is noticeable as the wavelength decreases, the use of the third-order focus improves the resolution of the system, and under certain conditions the depth of field can be increased without loss of resolution. The chromatic aberrations of the zone plate are not restrictive for a large number of applications.
5 citations
29 Aug 1977
TL;DR: The separation of the focused + 1st order ofdiffraction picture from the zeroth and -1st order patterns is discussed in this paper, where the authors put up therelation between temperature and density in the emitting regions and the energy density distributions in the corresponding pictures, including the effect of chromatic aberration.
Abstract: Photographs of coronal active regions,taken with Fresnel Zone plates were quantitative-ly analyzed. For this purpose the properties of absorption edge filters used for wave-length selection and of film sensitivity, as well as the imaging properties of FresnelZone plates were comprehensively investigated.The separation of the focused +1st order ofdiffraction picture from the zeroth and -1st order patterns is discussed. We put up therelation between temperature and density in the emitting regions and the energy densitydistributions in the corresponding pictures, including the effect of chromatic aberration.An iteration procedure was applied to solve the set of equations,which characterizes thisrelation, leading to two dimensional maps of temperature and emission measure as illustra-ted for one active region.IntroductionX -ray photography is an essential tool to investigate the solar corona because of thehigh spatial resolution achievable with imaging systems. e u n of a few arc secshas been reached with grazing incidence mirror
3 citations
20 Jan 1977
TL;DR: In this article, the utility of coded aperture imaging of radioisotope distributions in Nuclear Medicine is in its ability to give depth information about a three dimensional source, and the authors have calculated imaging with Fresnel zone plate and multiple pinhole apertures to produce coded shadows and reconstruction of these shadows using correlation, Fresnel diffraction, and Fourier transform deconvolution.
Abstract: The utility of coded aperture imaging of radioisotope distributions in Nuclear Medicine is in its ability to give depth information about a three dimensional source. We have calculated imaging with Fresnel zone plate and multiple pinhole apertures to produce coded shadows and reconstruction of these shadows using correlation, Fresnel diffraction, and Fourier transform deconvolution. Comparisons of the coded apertures and decoding methods are made by evaluating their point response functions both for in-focus and out-of-focus image planes. Background averages and standard deviations were calculated. In some cases, background subtraction was made using combinations of two complementary apertures. Results using deconvolution reconstruction for finite numbers of events are also given.
2 citations
TL;DR: In this paper, channeled spectra can be considered as temporal Fourier holograms provided they are displayed along a scale linear in wave-numbers, which can be achieved by using a spectrograph containing a holographic zone plate.
2 citations
29 Aug 1977
TL;DR: One-dimensional coded apertures have been investigated for use in imaging long, narrow objects such asreactor fuel pins as mentioned in this paper, and an iterative, nonlinear algorithm has been developed for removing the background produced by extra-core values in the point spread function.
Abstract: One- dimensional coded apertures have been investigated for use in imaging long, narrow objects such asreactor fuel pins. Since coded apertures work better for small, point -like objects, while pinhole apertureswork better for large extended objects, a hybrid aperture combining these properties seems attractive forimaging fuel pins. The one -dimensional aperture behaves like a coded aperture in the direction for whichthe object is small, while it acts like a pinhole in the direction for which the object is extended. A one - dimensional Fresnel zone plate has been investigated, and an iterative, nonlinear algorithm has been developedfor removing the background produced by extra -core values in the point spread function. The algorithm isshown to have a decidedly nonlinear effect on the effective system transfer function. Uniformly redundantsequences have also been investigated as possible aperture codes. They can produce filled apertures andresult in a decoded image with a uniform background level that can be easily removed by subtraction.IntroductionSpatial resolution in a pinhole imaging system is achieved by severely restricting the solid angle withinwhich photons are collected. When the limiting noise source is quantum (photon) noise, the signal -to -noiseratio (SNR) depends on the number of photons collected. Resolution requirements and SNR requirements aretherefore fundamentally in conflict. In a coded aperture imaging system, spatial resolution in the detectedimage is sacrificed in favor of increased collection efficiency. Instead of a pinhole, a larger aperturewith a known transmission function is placed between the object and the detector. If the aperture functionis chosen wisely, it is possible to recover the spatial resolution by processing the recorded or coded image.In order to determine how much of an advantage the coded aperture system has over the pinhole system, theSNR in the final decoded image can be compared with the SNR in the pinhole image. For the comparison to bevalid, the exposure time, the resolution in the final image, and the type of object must be specified.
29 Aug 1977
TL;DR: In this article, a coded aperture imaging system for the measurement of nuclear fuel motion in simulated core disruptive accidents is described, where a one dimensional Fresnel zone plate type coded aperture is used to modulate the fission gamma rays emitted from the fuel pin under test.
Abstract: A coded aperture imaging system for the measurement of nuclear fuel motion in simulated core disruptive accidents is described. A one dimensional Fresnel zone plate type coded aperture is used to modulate the fission gamma rays emitted from the fuel pin under test. Two active imaging systems have been developed to detect the coded image and record it on film using a high speed camera. The first system is an X-ray image intensifier which converts fission gamma rays to optical photons in a thin (0.1 mm) CsI(Tl) scintillator screen on which a photocathode is deposited. The photoelectrons thus created are collected and focused by electron optics and produce an image on the output phosphor. The second system utilizes a NaI(Tl) scintil-lator crystal and a separate high gain optical image intensifier to produce the desired coded image. With a few modifications both systems appear capable of achieving the preliminary design goals of 1 mm radial resolution, 5 mm axial (along the fuel pin axis) resolution and 1 msec temporal resolution. Presently, the X-ray image intensifier system offers the best resolution, but the second system provides higher gain and a wider selection of operating conditions. The temporal response of both systems is limited to a few milliseconds by the output phosphor. Experimental performance data for each system will be presented, and the results of pre-liminary nuclear fuel pin imaging experiment performed at the Sandia Pulsed Reactor will be shown.
01 Jan 1977
TL;DR: One-dimensional coded apertures have been investigated for use in imaging long, narrow objects such asreactor fuel pins as mentioned in this paper, and an iterative, nonlinear algorithm has been developed for removing the background produced by extra-core values in the point spread function.
Abstract: One- dimensional coded apertures have been investigated for use in imaging long, narrow objects such asreactor fuel pins. Since coded apertures work better for small, point -like objects, while pinhole apertureswork better for large extended objects, a hybrid aperture combining these properties seems attractive forimaging fuel pins. The one -dimensional aperture behaves like a coded aperture in the direction for whichthe object is small, while it acts like a pinhole in the direction for which the object is extended. A one - dimensional Fresnel zone plate has been investigated, and an iterative, nonlinear algorithm has been developedfor removing the background produced by extra -core values in the point spread function. The algorithm isshown to have a decidedly nonlinear effect on the effective system transfer function. Uniformly redundantsequences have also been investigated as possible aperture codes. They can produce filled apertures andresult in a decoded image with a uniform background level that can be easily removed by subtraction.IntroductionSpatial resolution in a pinhole imaging system is achieved by severely restricting the solid angle withinwhich photons are collected. When the limiting noise source is quantum (photon) noise, the signal -to -noiseratio (SNR) depends on the number of photons collected. Resolution requirements and SNR requirements aretherefore fundamentally in conflict. In a coded aperture imaging system, spatial resolution in the detectedimage is sacrificed in favor of increased collection efficiency. Instead of a pinhole, a larger aperturewith a known transmission function is placed between the object and the detector. If the aperture functionis chosen wisely, it is possible to recover the spatial resolution by processing the recorded or coded image.In order to determine how much of an advantage the coded aperture system has over the pinhole system, theSNR in the final decoded image can be compared with the SNR in the pinhole image. For the comparison to bevalid, the exposure time, the resolution in the final image, and the type of object must be specified.
TL;DR: In this paper, a theoretical study of the variation of relative field amplitude with axial distance has been made for a plane and a spherical microwave zone plate with an incident plane wave front having non-uniform aperture excitation distribution.
Abstract: A theoretical study of the variation of relative field amplitude with axial distance has been made for a plane and a spherical microwave zone plate with an incident plane wave front having non-uniform aperture excitation distribution. The results show a sharper focussing property for the non-uniform excitation.