Showing papers on "Fresnel zone published in 1977"
TL;DR: In this paper, the radiated far field is determined from a rapidly convergent series representation of the radiation integral, where the coefficients of the series are independent of the observation angles, and the field may be determined very rapidly at large numbers of points.
Abstract: Given the true or any approximate current on a reflector, the radiated far-field is determined from a rapidly convergent series representation of the radiation integral. The leading term is a well-shaped J_{1}(x)/x beam pointing in a desired direction. Higher order terms provide perturbations to the leading term. The coefficients of the series are independent of the observation angles. Hence, once they are computed, the field may be determined very rapidly at large numbers of points. Initially, a suitable small angle approximation is made that places the radiation integral in the form of a Fourier transform on a circular disk. The theory is then extended such that the results are valid in both the near and the wide angle regions. Application to a rotationally symmetric paraboloid is presented herein. Other applications include the offset and dual reflectors and near- to far-field integrations. A modified form of the series can also be used for Fresnel zone computations.
110 citations
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
Patent•
20 Jun 1977
TL;DR: In this paper, the distribution over n successive elementary transducers of the phases corresponding to focusing at a predetermined distance or several successive distances from the line is stored, which corresponds to several Fresnel zones.
Abstract: N elementary transducers are distributed regularly along a line of scanni An ultrasonic frequency receiver is associated with phase lag means. The distribution over n successive elementary transducers of the phases corresponding to focusing at a predetermined distance or several successive distances from the line is stored. That distribution corresponds to several Fresnel zones. Switches first connect a generator to a group of n' transducers corresponding to the central Fresnel zone of said stored distribution and later connect a group of n transducers to the receiver direct and via the phase lag means according to the stored distribution(s). The groups of n' and n elementary transducers are shifted along the line at intervals of time. The phase lag means may consist of inverter means causing a phase angle of π.
27 citations
TL;DR: In this article, a laser beam is generated free of physical contact in a light absorbing workpiece by the use of laser beam means providing a coherent light beam which in a pulsed manner impinges upon the surface of the workpiece in a Fresnel zone pattern.
Abstract: Focussed acoustic waves are generated free of physical contact in a light absorbing workpiece by the use of laser beam means providing a coherent light beam which in a pulsed manner impinges upon the surface of the workpiece in a Fresnel zone pattern. The zoned pattern is caused in a typical example by a suitable mask interposed between the laser source and workpiece surface. The thermal effect responsive to the laser beam energy produces in the workpiece a plurality of acoustic waves having a common focal point.
24 citations
Patent•
3M1
TL;DR: In this paper, a retroreflective material including a medium containing a plurality of diffraction elements comprising light interference fringe patterns is formed by pressing a first medium having on a surface thereof a multiplicity of light interference fringes defining an array of phase modulated fresnel zone plates onto a surface of a copy medium having a thickness equal to a given focal length associated with the fresnel zones plates and a reflective material is coated on the opposite surface of the copy medium.
Abstract: Retroreflective material including a medium containing a plurality of diffraction elements comprising light interference fringe patterns is formed by pressing a first medium having on a surface thereof a plurality of light interference fringe patterns defining an array of phase modulated fresnel zone plates onto a surface of a copy medium having a thickness equal to a given focal length associated with the fresnel zone plates and a reflective material is coated on the opposite surface of the copy medium. In making other embodiments a plurality of fringe patterns is recorded throughout the volume of a photosensitive medium.
21 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
TL;DR: In this article, the authors compare the signal to noise ratio between images obtained either by a Fresnel zone or by an annulus at equal resolution, and show that the noise depends on the type of code.
16 citations
8 citations
TL;DR: In this article, the first step of a Fourier expansion is used to calculate particle velocities induced by disc-shaped transducers which are assumed perfectly damped and excited by a step wise function.
7 citations
TL;DR: In this article, four-frequency and two-stage three-frequency interactions are considered as the basis of two autocorrelation methods, and the second method is more effective in the case of non-centrosymmetric media.
Abstract: Four-frequency and two-stage three-frequency interactions are considered as the basis of two autocorrelation methods. The second method is more effective in the case of noncentrosymmetric media. Autocorrelations of objects obtained experimentally are reproduced and it is shown that autocorrelators can be used to cancel out the phase distortions introduced in the Fresnel zone.
TL;DR: In this paper, a theoretical analysis of the efficiency of a system for the compensation of phase fluctuations of an optical wave traveling in a turbulent atmosphere is made and a correlation function for the uncompensated error and the compensation parameter a are introduced.
Abstract: A theoretical analysis is made of the efficiency of a system for the compensation of phase fluctuations of an optical wave traveling in a turbulent atmosphere. In this system the distortions are compensated on the basis of measurements of phase fluctuations in the reflected wave. A correlation function for the uncompensated error and the compensation parameter a are introduced. Calculations carried out in the approximation of smooth perturbations indicate that the compensation on the basis of reflected waves is effective only up to distances at which the Fresnel zone does not exceed the external scale of turbulence.
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.
TL;DR: Ordinary optical components may behave in extraordinary ways when illuminated with ultrashort optical pulses, but only the flat lenses such as Fresnel lenses, Fresnel zone plates, and holographic lenses display such anomalies.
Abstract: Ordinary optical components may behave in extraordinary ways when illuminated with ultrashort optical pulses. In the cases of lenses, only the flat lenses such as Fresnel lenses, Fresnel zone plates, and holographic lenses display such anomalies. For them, the pulse may be both elongated temporally and spread spatially unless very high focal number lenses are used.
21 Nov 1977
TL;DR: In this paper, an analogous lens model was proposed to focus light exactly the same as a holographic optical element, which can be used for on-axis, off-axis and any wavelength.
Abstract: Holographic optical elements (photographically produced Fresnel zone plates) can be easily designed with lens design computer codes using an analogous lens model. From a ray tracing point of view this lens model focuses light exactly the same as a holographic optical element. The analog works for on-axis rays, off-axis rays and any wavelength.© (1977) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
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
Journal Article•
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.