Showing papers on "Fresnel zone published in 1988"

Computer-generated holograms of 3-D objects composed of tilted planar segments.

Abstract: The Fresnel diffraction of tilted planar objects is determined. It can be calculated by a Fourier transformation, a coordinate transformation, and a subsequent multiplication by a quadratic phase. Images of 3-D objects are composed by superimposing several planar segments. The resultant complex amplitude is coded and stored in a computer-generated hologram. Optical reconstructions of planar segments nearly parallel to the optical axis are demonstrated.

Flat printed reflector antenna for mm-wave applications

Abstract: An antenna consisting of a flat printed reflector and a feed horn was investigated at mm-wave frequencies. The dielectric material is fully metal covered at the side opposite to the feed, whereas the side facing the feed is provided with a number of metallic annular rings forming a Fresnel zone plate. >

Area in phase space as determiner of transition probability: Bohr-Sommerfeld bands, Wigner ripples, and Fresnel zones

Abstract: We consider an oscillator subjected to a sudden change in equilibrium position or in effective spring constant, or both—to a “squeeze” in the language of quantum optics. We analyze the probability of transition from a given initial state to a final state, in its dependence on final-state quantum number. We make use of five sources of insight: Bohr-Sommerfeld quantization via bands in phase space, area of overlap between before-squeeze band and after-squeeze band, interference in phase space, Wigner function as quantum update of B-S band and near-zone Fresnel diffraction as mockup Wigner function.

Formation of negative-index-change waveguide lenses in LiNbO(3) by using ion milling.

Abstract: We report, for the first time to our knowledge, fabrication of two types of negative-index-change waveguide lens in LiNbO3 by using ion milling. The first type is an analog Fresnel lens formed by grooves milled into the waveguide. The second is a hybrid lens that combines analog Fresnel zones in the central region with chirp gratings on the sides formed by the same means. We have obtained simultaneously high-efficiency and near-diffraction-limited focusing characteristics in both types of lens. The ion-milling technique employed should be capable of producing similar lenses in any other waveguide substrate, such as GaAs.

Diffraction modelling of 3-D lower-crustal reflectors

Abstract: SUMMARY The length of the acoustic path and the limited band-width of the lower crustal reflections in near-normal-incidence profiles give a Fresnel Zone radius of the order of 2-3 km for the lower crust. In this situation, interpretations of the lower crust cannot be based solely on geometrical optics, which is a high-frequency approximation, but must take into account the effects of diffraction. A mathematical model based on the Kirchhoff Integral estimates diffraction effects in the acoustic field and allows the reflections observed from a laterally varying, first-order discontinuity to be calculated for arbitrary source and receiver locations. A simplified form of the Kirchhoff Integral provides a clear physical model for the form of the reflected field including diffraction effects. This model is used to study synthetic sections and several useful interpretational rules for deep reflection data are inferred. The simplified formula indicates the limitations of interpretations based on geometrical optics. It shows that although geometrical optics cannot explain the amplitudes of the reflected image, it does correctly predict the arrival-times of the major observed reflections. This justifies a depth migration method based on ray-tracing.

Diffraction patterns in the shadows of disks and obstacles.

Abstract: We compare the Fresnel diffraction pattern of a thin circular disk with that of a square obstacle, specifically evaluating the on-axis field strength. Photographs of the diffraction patterns reveal some curious features for the square obstacle. Second, the precise electric and magnetic fields behind a conducting circular disk are evaluated without invoking the Fresnel approximation and contrasted with the rigorous electromagnetic result for a metal sphere. The calculations show that the two cases differ only slightly in the Fresnel region. In the near-field new computational results for the sphere are analyzed.

Phase retrieval radio holography in the Fresnel region: tests on the 30 m telescope at 86 GHz

Abstract: The application of phase retrieval radio holography in the Fresnel region has been studied using a 86 GHz transmitter as signal source. Maps of the aperture-plane field distribution were made with a surface resolution of about 100 independent pixels across the telescope diameter. Over the 2.7 km propagation path used (0.005 of the farfield distance), the measurement accuracy was found to be determined by atmospheric scintillation. The root mean square measurement errors in the derived aperture-plane phase distribution were about 65 microns when expressed as axially resolved surface errors. The signal to noise ratio and dynamic range requirements are easy to fulfill in the Fresnel zone, while the necessary near field corrections can be applied with high accuracy. There are thus definite advantages to phase retrieval radio holography in this near field zone.

High‐resolution Fresnel zone plates for soft x rays

Abstract: Fresnel zone plates with minimum zone widths down to 50 nm were fabricated by electron‐beam lithography, tested, and used in the scanning x‐ray microscope at the Brookhaven National Synchrotron Light Source. The zone plates consist of gold rings on a silicon nitride window. Characterization of the zone plates included efficiency and resolution measurements in the first order focus. Spatial resolution down to 75 nm was measured. The best zone plates showed negligible astigmatism, and a first order efficiency in excess of 5% has been achieved. A new method for development monitoring during the fabrication procedure using an optical microscope with polarized light and crossed analyzer was introduced. For the inspection of the fabrication accuracy and, in particular, for ellipticity, a moire pattern technique was employed. Using these zone plates as objective lenses, x‐ray images of biological specimens were obtained with 70 nm resolution.

Fresnel zone plate (Fresnel lens) as a reflector for a microwave transmitting/receiving antenna

Abstract: A Fresnel zone-plate reflector of a transmitting/receiving antenna contains a flat metal reflector and a plurality of concentrically arranged metal circular rings in a plane parallel to the reflector and at a spacing of a quarter of a wavelength, such that the wave elements of a spherical wave front reflected on the circular rings are added in the correct phase to the wave elements reflected (in the ideal case) on the reflector surface, to form a flat wave front.

Statistical Modelling of Lower-Crustal Reflections

Abstract: SUMMARY a geological feature to be resolved in a seismic reflection profile its size must be comparable with the dimensions of the Fresnel zone for its depth and the frequency-content of the seismic wavefield. Since the diameter of the Fresnel zone is over 5 km for lower-crustal reflections, the effects of variations of the crust on smaller length scales must be considered when interpreting deep reflection profiles. Modelling the seismic wavefield using first-order scattering theory shows how the reflections observed in a small-offset profile are affected by the statistical distribution of elastic vanations within the crust. Crustal heterogeneities on length-scales smaller than the seismic wavelength cause frequency-dependent attenuation which can be comparable with the losses due to anelastic absorption. Larger scale elastic variations cause rapid loss of coherence in the seismic field. The observation of deep seismic reflections can thus be used to constrain the degree to which the crustal elasticity varies on small length scales. Coherent seismic reflections from the lower crust limit the fractional variation of elasticity averaged over the entire crust to a few percent on a wide range of length-scales.

Average intensity and contrast of light amplified by a partially homogeneously broadened, slightly saturated laser amplifier with stochastic gain distributions.

Abstract: We evaluate the average intensity and contrast of the output of a laser amplifier in which stochastic gain distributions exist This situation occurs when turbulence flows are developed in a gas- or liquid-laser amplifier The gain medium is assumed to be partially homogeneously broadened and slightly saturated and to consist of two-level atoms In our computations, a plane wave is propagated through the gain medium with weak turbulences, under the assumption that the size of the first Fresnel zone is much smaller than the characteristic length of turbulences

Collapsible receiving antenna

Abstract: Flat antennas such as Fresnel zone plates may be used to receive microwave signals. Such antennas are mounted on windows (4) and focus the signals on a horn feed (10). This invention discloses a flexible Fresnel zone plate (1) adapted to be wound on a cylindrical member (3) similar to that used in a roller blind. The antenna may thus be readily mounted against a window (4), and the Fresnel zone plate unwound to receive signals.

Bragg-Fresnel Optics: Principles and Prospects of Applications

Abstract: Possibilities of control and focusing of X-rays have been discussed repeatedly since the discovery made by Rontgen. It turned out, however, that applications of the principles of optical element fabrication adopted in visible light, infrared radiation and other wavelength ranges are rather limited due to negligible difference of the refractive index from unity, a relatively large absorption coefficient and the necessity to fabricate optical elements with the accuracy compared to a radiation wavelength. In the last years the methods of X-ray optics acquire further extensive development because of the advances in microstructuring technology, namely, structure fabrication with element sizes up to one hundred angstroms, sputtering technology and that of the growth of thin films of different materials, and due to the advances in the investigation of X-ray diffraction. In our opinion, at present there exists a possibility to set and solve the task of fabricating effective focusing X-ray elements with the structure of three-dimensional Fresnel zones, that is, Bragg Fresnel optics. These elements can be made on the basis of multilayer interference mirrors for the nanometer wavelength range (0.5nm≲λ≲10nm) and semiconductor perfect crystals with heterostructures for the wavelength range of 0.1A≲λ≲5A. The principal peculiarity of Bragg-Fresnel X-ray elements lies in the fact that coherent Bragg scattering by separate layers is used in them. As it will be shown, this phenomenon permits increasing their diffraction efficiency, widening the spectrum range and angular aperture and gives a possibility to realize amplitude and phase modulations of radiation, to switch X-ray elements by an electrical signal, ultrasound and light signals.

Phase-retrieval technique for antenna metrology

Abstract: A modified form of the Misell algorithm has recently been suggested which makes the original proposition a viable practical alternative for phaseless antenna metrology. In the letter a different form for the modified Misell algorithm is suggested using diffraction filters.

Optical coupling structure between light source and light guide circuit component

Abstract: PURPOSE:To simplify an optical coupling structure and to attain size reduction and economization by using only a Fresnel zone lens formed on one end surface of the substrate of a light guide circuit component as an optical coupling element between a light source and the light guide circuit components. CONSTITUTION:The light guide circuit component 12 has the substrate 13 and a light guide 14 extending from its one end surface 13a along one flank 13b. Further, the Fresnel zone lens 15 which converges and guides light emitted by the light source 11 to the light guide 14 is formed on one end surface 13a of the substrate 13. At this time, the Fresnel zone lens 15 is formed larger than the size of the end surface of the light guide 14, so the light emitted by the light source 11 is guided through the Fresnel zone lens 15 into the light guide not only from the end surface of the light guide 14, but also from its periphery to perform optical coupling with high coupling efficiency. Consequently, the optical coupling structure which is simple and formed at low cost to small size is obtained between the light source and light guide circuit component.

Micro-fresnel lens

Abstract: PURPOSE:To facilitate the manufacture and to decrease the chromatic aberration by specifying the height of an uneven pattern in each Fresnel zone. CONSTITUTION:Height of an uneven pattern of each zone is set to a value for giving a phase shift of 2npi (n is a positive integer of >=2). Accordingly, a period of each zone becomes two times, comparing with a conventional Fresnel lens having a value for giving a phase shift whose height is 2pi. That is, even in case of the same numerical aperture NA, the period of each zone becomes (n) times by setting the height of the lens to (n) times. In such a way, the manufacture accuracy is improved, the lens efficiency is raised, and also, the period of the Fresnel zone is lengthened, by which a light beam is curved by a refraction rather than a diffraction effect, and a chromatic aberration caused by a use wavelength variation is decreased.

Imaging zone plates for x‐ray microscopy fabricated by electron‐beam lithography

Abstract: Fresnel zone plates have been fabricated by electron‐beam lithography using a modified scanning transmission electron microscope. These microzone plates are designed to work as imaging elements in an x‐ray microscope. To achieve zone plates that are free of distortions, the deflection field of the lithography system has been calibrated by the aid of externally generated reference marks. Microzone plates with a minimum linewidth of 20 nm have been written into polymethylmethacrylate and etched into a 15‐nm‐thick titanium layer. Two methods of transfer into a gold absorber layer have been used, namely sputter etching of the gold layer with a reactively ion etchedtitanium mask, and electroplating of gold using a suitable trilevel resist system. By these techniques, Fresnel zone plates with 100 zones, a width of the outermost zones of 50 nm, and a thickness of the gold absorber layer of 80 nm have been fabricated. Imaging experiments have been performed at the electron storage ring BESSY in Berlin, and the results have been compared with images obtained by holographically fabricated zone plates.

Measurement of Resolution in Zone Plate X-Ray Microscopy

Abstract: Image formation in scanning x-ray microscopy is achieved by rastering a semi transparent specimen across a small x-ray probe and counting the number of photons transmitted by the specimen at position of the scan. The finest soft x-ray probes generated so far have been produced by modified fresnel zone plates [1,2]. In scanning x-ray microscopy a zone plate is used to demagnify a source of x rays. The dimensions of the probe are primarily determined by the width of the finest zone (dr) of the zone plate. If the zone plate has been fabricated with sufficient accuracy and is illuminated with x-rays which are both spatially and temporally coherent then the probe shape will resemble an airy pattern which has a full width at half maximum (FWHM) which is very nearly equal to the finest zone.

Microzone Plate Fabrication by 100 keV Electron Beam Lithography

Abstract: Fresnel zone plates which are used as imaging lenses for soft x-rays are required to have high resolution, high efficiency, and low distortions. In terms of practical realisation, this means smallest possible widths of the outer zones, high aspect ratios of the absorber rings, and a positional accuracy of the structures to a fraction of the outer zone width. Additionally, the absorptance of the membranes carrying the zone plate has to be minimized.

A Zone Plate Soft X-Ray Microscope Using Undulator Radiation at the Photon Factory

Abstract: A soft X-ray microscope using Fresnel zone plates as optical imaging elements has been developed inthelast few years at an undulator beamline BL-2 of the Photon Factory. As was already reported, /1/ magnified images of copper #1000 and #2000 meshes were obtained preliminarily. In this paper, we describe the new version of the soft X-ray microscope with the improved optical and mechanical arrangements, and report some recent results newly obtained with the improved system.

Characteristics of optical components for soft x-ray microscopy and x-ray holography using an undulator radiation optical system

Abstract: X‐ray optical components, including Fresnel zone plates and transmission gratings, have been fabricated using finely focused electron beam lithography and Ta‐on‐SiN x‐ray mask fabrication technology The optical components for x‐ray microscopy and x‐ray holography were evaluated in an undulator radiation optical system

Future Plans for X-Ray Microscopy at the SRS

Abstract: The recent up-grade of the synchrotron radiation source (SRS) at the Daresbury Laboratory provides an improved low emittance photon source In particular, the existence of a high brilliance source of x-radiation, and the need to provide diffraction limited optics for high resolution microscopy, has stimulated the re-examination of the problem of matching the x-ray source to the x-ray microscope

Infra-red intrusion detector.

Abstract: The detector, which analyses the infrared radiation of an intruder to trigger an alarm signal output, produces a strip-shaped radiation reception zone (E3, E4) forming a security curtain, with a sharp demarkation and uniform sensitivity irrespective of the angle of incidence of the radiation and with an enlarged angle of opening due to the use of a cylindrical Fresnel lens (8) of small thickness and bent in the longitudinal direction in such a manner that the radiation sensor (2) is at the focus of the bent cylindrical Fresnel lens (8). The cylindrical Fresnel lens (8, 81, 82) is preferably bent in the longitudinal direction to form an arc with a radius (r) corresponding to its focal length, the sensor (2) being at least approximately in the centre of the circle and at the focal point of the cylindrical Fresnel lens (8, 81, 82). In further embodiments an advantage is obtained in that the sensor (2) is designed as a dual sensor with a plurality of sensor elements (3, 4), which work together with one or more cylindrical Fresnel lenses thus forming a plurality of radiation reception zones (E3, E4).

Scanning X-Ray Microradiography and Related Analysis in a SEM

Abstract: Current scanning x-ray microscopes or microprobes require x-ray optics such as Fresnel zone plates and mirror systems. Because of different loss factors /1/ these systems need high photon flux sources, such as synchrotron radiation (SR). Despite this, the resulting x-ray photon density still remains in the 107 – 109ph/(s μm2) range. As shown by WITTRY and GOILIJANIN /2/, such values can be obtained from a classical source combined with a toroidal curved crystal, a system which affords all the advantages of a laboratory source in comparison with SR.

Fresnel zone plate

Abstract: PURPOSE:To decrease generation of aberrations with respect to axial and offaxial condensing points by satisfying sinusoidal conditions as well as the time of designing the annular zonal boundary radii of respective Fresnel zones CONSTITUTION:The 1st and 2nd Fresnel zones 31, 32 co-possessing the optical axis on both faces on the spot light source side and condensing point side of a parallel flat plate 3a and are so designed that the annular zonal boundary radii r1,k and r2,k (k=1,2,3) of the 1st and 2nd Fresnel zones 31, 32 satisfy the following two conditions: The luminous flux emitted from the spot light source placed at a prescribed distance from the plate 3a on the optical axis is condensed without aberrations to the condensing point on the optical axis The luminous flux emitted from the spot light source off the optical axis deviated in the direction perpendicular to the optical axis from the spot light source on the optical axis is condensed without aberrations to the condensing point off the optical axis deviated in the direction perpendicular to the optical axis from the condensing point on the optical axis Even the object point deviated from the optical axis of the Fresnel zones is thereby condensed to the image point with substantially no aberrations

Linear fresnel zone

Abstract: PURPOSE:To enable accurate positioning between a mask and a wafer, by providing a curved condenser part following a linear condenser part to eliminate effect of scattered light caused by ends of the linear condenser part. CONSTITUTION:A linear Fresnel zone 1 is set at a specified position of a mask 6 and an alignment light irradiated with linear condenser parts 11 and 12 are condensed to prescribe the mask 6 at a position determined on the wafer 5 irradiating a positioning mark 5a set on the wafer 5. Then, curved condenser parts 3a and 3b are arranged successively on both sides of the parts 11 and 12 to condense the alignment light irradiated to the parts 3a and 3b following both ends of the parts 11 and 12. This eliminates effect of scattered light due to ends of the parts 11 and 12 thereby enabling accurate positioning between the mask 6 and the wafer 5.

Blazed Zone Plates For The Infrared

Abstract: A blazed zone plate has been made in germanium by ion etching, into the surface, a circular fringe pattern recorded in photoresist. An efficiency of 64% at 10.6 pm was measured which is consistent with independent measurements of the groove profile. 1. INTRODUCTION It has long been known that a plate in which alternate half period Fresnel zones are rendered opaque can be used to produce focused images. It is the diffracting equivalent of a lens and has a series of focal lengths corresponding to different orders of diffraction. The efficiency in any diffracted order is therefore low and since the focal length is inversely proportional to wavelength it also has very severe chromatic aberration. For these reasons zone plates have not been considered as serious alternatives to lenses. However, since they are thin structures they do offer the advantages of low weight, lower substrate costs and the possibility of being made very cheaply by replication. In the infrared there are many applications where these advantages are significant. It is the purpose of the present paper to describe methods of making zone plates of improved performance and to consider whether such improvements will be sufficient to enable designers to take advantage of the benefits that these devices have to offer.In a single element it is impossible to avoid the fact that the focal length is inversely proportional to wavelength. In order avoid chromatic aberration one may have to work with monochromatic light (with the increasing use of lasers and light emitting diodes there are many applications where this is a realistic option). Achromatism can be achieved in a compound system if the elements are separated, but the efficiencies in each element must be high if the overall efficiency is to be acceptable.The distribution of light into the various orders, and hence the efficiency in a particular order is determined by the shape of the amplitude and phase function across each zone. The highest efficiencies are achieved when only the phase is modulated and when the zone plate consists of a series of grooves of triangular cross section. This is the circular equivalent of the familiar blazed diffraction grating in which the facets of each groove behave as minute prisms and deflect the light by refraction into the same direction as that determined through diffraction by the periodic structure. By this means a high proportion of the incident light may be concentrated into a single diffracted order and in principle it should be possible to achieve efficiencies which are comparable with those of lenses.

Design of sound source with fresnel‐zone pattern and its field analysis

Abstract: When an interdigital transducer (IDT) is loaded with a liquid, an acoustic beam can be excited in the liquid. To focus this acoustic wave in the liquid, the authors have used an IDT that is divided in a Fresnel zone type in the direction of the electrode aperture. From a theoretical calculation of the focused acoustic field generated by the Fresnel zone IDT, it is found that the point of maximum sound pressure is closer to the electrode than the designed focal point. To find the cause of this discrepancy, the acoustic field excited by the Fresnel zone source is analyzed. It is found that a modification in the design model of Fresnel zone IDT's is needed due to the difference between the two- and three-dimensional fields. A new optimum design method is proposed in which the focal point obtained from field analysis and that obtained from the electrode design model coincide.