Showing papers on "Fresnel zone published in 1989"

The Fresnel zone and its interpretive significance

Abstract: Resolution of the reflection seismic record in the temporal (vertical) dimension has historically dominated the attention of geophysicists The ability to “resolve” two reflectors with close vertical spacing is of particular importance in stratigraphic analysis However, resolution is most completely understood when it is considered in a three‐dimensional sense To what extent can the seismic method resolve a point? If we can understand the resolution limits of seismic sections for expressing a point acoustic discontinuity in subsurface space, then the question of resolution is answered for any reflector configuration (since, under Huygens’ principle, all reflection surfaces may be represented as sufficiently dense arrays of point diffractors)

Resolution doubling lithography technique

Abstract: A lithography system is disclosed which is capable of doubling the spatial frequency resolution associated with conventional systems. A spatial filter, positioned to intercept the Fraunhofer diffraction pattern of the mask being exposed, is configured to prevent certain orders of the diffraction pattern (in most causes the O-order and ±2nd, 3rd, . . . orders) from reaching the wafer's surface. The remaining orders reaching the wafer surface (in most cases the ± first-order beams) will produce a cos-type interference pattern with a period half of that if the mask grating were imaged without spatial filtering. Therefore, for a system with a given magnification factor m, a mask grating with a period p will be exposed on the wafer surface as a grating with a period of p'=pm/2. Advantageously, the spatial filtering technique of the present invention allows for a variety of different structures (conventional gratings, chirped and phase-shifted gratings, grids, Fresnel zone plates, etc.), as well as structures of different sizes and orientations, to be included on one mask and transferred to the wafer with a single exposure cycle.

Electrically-controllable thin film Fresnel zone device

Abstract: An optical component comprises a thin film of an electrically controllable birefringent material confined between substantially planar surfaces. A respective electrode structure is provided on each of the surfaces, each electrode structure being patterned such that an electric field applied across the film by means of electrode structures, when a voltage is applied therebetween, causes modulation of the refractive index of the material such that the wavefront of electromagnetic radiation incident of the component and transmitted through the thin film is divided into Fresnel zones.

Position detector employing a sector fresnel zone plate

Abstract: A position detector for use with an X-ray exposure apparatus and the like includes sector Fresnel zone plates (SFZP) which are provided on a mask (14) and a wafer (15) minutely spaced in position in the direction of the optical axis of an exposure X-ray, as alignment marks (16, 17). A laser ray of at least one wavelength is applied to the surfaces of the SFZPs at an angle with respect to the surfaces. The SFZPs are designed such that the principal focal planes of Fresnel diffraction images of the SFZPs to a single wavelength laser ray agree with each other. In the case of illumination rays of a plurality of wavelengths, an objective lens (9) is provided in a detection optical system (10) which objective has such an axial chromatic aberration that focal planes of the objective lens to the plural wavelength rays agree with respective Fresnel diffraction focal planes of the SFZPs to the rays. The image formed on the superposed focal plane of the objective lens is converted into an electric signal, which is handled to detect a relative position between the mask and wafer in the direction perpendicular to the surface thereof.

Numerical study of the diffraction of elastic waves by fluid‐filled cracks

Abstract: The diffraction of P-SV waves by one or several fluid-filled cracks is simulated numerically. The method used is based on the integral representation of the diffracted field. We establish the integral representation for fluid-filled cavities embedded in elastic media, and we compute the boundary integral equation by discretizing the diffracting surface and by evaluating Green's functions by the discrete wave number method. We compare the effects of the diffraction by a single crack versus a fracture system consisting of several shorter cracks, for low and high frequencies, with and without the single scattering (Born) approximation. At low frequencies the cracks interact individually; the energy diffracted is weak compared with the incident energy and exhibits a large dependence with respect to the crack length. For higher frequencies, interactions between cracks are predominant; the single crack and multiple cracks present similar radiation and amplitude patterns for diffracted waves. The effects are close to the ray theory results if the first Fresnel zone is of the same order as the crack extension.

Fraunhofer diffraction by volumetric bodies of constant thickness

Abstract: Explicit expressions for Fraunhofer diffraction patterns (spectra) of absolutely black bodies of constant thickness have been derived from the model of equivalent diaphragms in the Kirchhoff–Fresnel approximation. The expressions can be interpreted as results of interference between generalized point sources with corresponding amplitudes and Fresnel radiation diagrams located at boundary points of the object. Approximation of the Fresnel radiation diagrams by elementary functions is suggested for analytical estimation. For essential simplification of calculations, the quasi-geometrical approach has been developed, according to which the light diffraction by faces of the object is taken into account and propagation of diffracted waves in free space is described in the geometrical-optics approximation. The extension of objects is shown to result in Fresnel modulation of their spectra and also in disturbance of the equidistant position of diffraction minima. There is agreement between theoretical and experimental results.

Diffraction calculations in the near field and the validity of the Fresnel approximation

Abstract: The general theory of the diffraction and propagation of light is considered. Particular attention is paid to the case of uniformly illuminated rectangular or circular apertures, for which the derivative of the field given by the Fresnel approximation is evaluated exactly. The limitations of the Fresnel approximation are considered, and thus a useful, simple way of understanding its validity is produced. This treatment yields an estimate of the accuracy of the Fresnel approximation in the general case and a method by which a modified Fresnel treatment can be used over a substantially extended region.

Modified reflectance and geometrical deformations of Gaussian beams reflected at a dielectric interface

Abstract: The geometrical interpretation of Gaussian-beam deformations under reflection at a linear dielectric interface is revised. It is proved that, besides the four known geometrical effects, namely, the lateral, focal, and angular shifts and the beam-waist modification, an independent nonspecular effect termed the complex amplitude modification exists and that all these effects are necessary for a complete description of the deformed beam. The new effect is described as a product of reflectance and propagation nonspecular modifications. The amplitude-based and intensity-based definitions of the modified reflection coefficient are given, and substantial differences between them and the Fresnel reflectance are shown. The significance of the propagation modification in the evaluation of the modified reflectance is also explained. Analytical expressions for all the nonspecular effects and for the interrelations among them are derived, and an accurate numerical procedure for their evaluation is discussed.

Fresnel diffraction by spherical obstacles

Abstract: Lommel functions were used to solve the Fresnel-Kirchhoff diffraction integral for the case of a spherical obstacle. Comparisons were made between Fresnel diffraction theory and Mie scattering theory. Fresnel theory is then compared to experimental data. Experiment and theory typically deviated from one another by less than 10 percent. A unique experimental setup using mercury spheres suspended in a viscous fluid significantly reduced optical noise. The major source of error was due to the Gaussian-shaped laser beam.

Propagation characteristics in land mobile satellite systems

Abstract: A description is given of experiments on land mobile satellite systems carried out with the Engineering Test Satellite-V (ETS-V) at 1.6 and 1.5 GHz. Typical propagation characteristics observed, a received power distribution measured in a local area, and estimation methods for received signal variations caused by a building and a single tree are described. It is shown that the shadowing effects of a building can be estimated exactly from a knife-edge diffraction model. Single-tree attenuation can be estimated from the relation between the area of the first Fresnel zone and the area that the tree occupies in it. It is concluded that mobile satellite communication services are achievable on about 90% of the main road in the area including local cities in Japan. >

Soft x-ray microscope at the undulator beamline of the Photon Factory

Abstract: A soft x‐ray microscope using Fresnel zone plates as optical imaging elements was installed at the Photon Factory. It makes use of undulator radiation as a source of soft x rays ranging from 2.0 to 3.0 nm in wavelength. The optical system was designed to match to the undulator radiation. A performance test was made at 2.66 nm by various pitches of transmission gratings. Those magnified images were taken with a magnification of 230 and exposure times of about 10 s. The modulation transfer function was measured over the spatial frequency up to 3300 lp/mm. Further, magnified images of some biological specimens were obtained.

Fabrication of diffraction X-ray elements

Abstract: The use of focusing elements in the X-ray range shows promise for nondestructive chemical analysis of samples with spatial resolution up to fractions of a μm. This paper considers the problems of fabricating Fresnel zone plates of different types: amplitude- and phase-transparent zone plates and reflective zone plates formed on a multilayer mirror, as well as microstructures with a specified zone profile.

Back projection type stereoscopic video projection televiation

Abstract: PURPOSE: To improve the stereoscopic feeling of a video by using such a Fresnel lens sheet that the mean birefringence in the plate thickness section of the Fresnel lens sheet satisfies a specific condition. CONSTITUTION: The subject projection television is constituted by using the Fresnel lens sheet 2 whose mean birefringence ▵n in the plate thickness section satisfies expression 1, where (t) is the thickness of the Fresnel lens sheet 2, λis the wavelength of light transmitted through the Fresnel lens sheet 2, and θ 1 is the angle of refraction after the incidence of light on the Fresnel lens sheet 2. Consequently, the polarization deviation of image light 3 which is already polarized due to the birefringence presenting in the plate thickness section of the Fresnel lens sheet 2 constituting a screen can be suppressed below a specific value as a phase difference, so the video light 3 which is polarized circularly to the right or left or polarized horizontally or vertically so as to obtain a stereoscopic video can be projected on the screen. Consequently, the video which provides stereoscopic feeling can be observed. COPYRIGHT: (C)1991,JPO&Japio

First surface Fresnel reflector for liquid crystal display

Abstract: A liquid crystal display assembly (10, 18, 22) for use with a reflective type overhead projector (28) includes a liquid crystal display (10). The liquid crystal display includes a Fresnel reflector with variable width grooves (24) which reduce double imaging which usually occurs with reflective type overhead projectors (28).

The Focusing Performance of Zone Plate Transducers

Abstract: Theoretical study of the focusing performance of different types of Fresnel-zone plate (FZP) transducers shows that the positive and negative patterns exhibit significantly different focusing characteristics when the number of zones is less than ten. The study also shows that for B-scan imaging, high resolution and effective sidelobe reduction can be obtained by using a single-ring annular transducer for transmitting in combination with a two-phase FZP transducer for receiving.

Focusing properties of Bragg-Fresnel lens in white spectrum of synchrotron radiation (abstract)

Abstract: The investigation results on details of the imaging by Bragg‐Fresnel lens (BFL) in white spectrum of synchrotron radiation are presented. BFL was fabricated on a silicon single crystal with the reflecting plane (III) by the methods of microlithography and plasma‐chemical etching. The relief depth of the zone structure was 3 μm, the last zone was 0.5 μm in size, the total width of the zone plate was 200 μm. The superconducting wiggler installed at the storage ring VEPP‐2M was used as a source of synchrotron radiation. The experimental results on the radiation focusing at different wavelengths (λ=1÷2.5 A) were obtained. The results include the focusing both in‐ and outside the focal plane of the zone plate. The results are also presented on an observation of the focusing in antibragg diffraction geometry when the orientation of Fresnel zones coincides with the vertical section of initial incident beam of radiation. The obtained results are treated analytically.

Interference of diffracted multiple wavefronts in the geometric shadow of the Fresnel region.

Abstract: A general diffraction analysis is presented to determine the irradiance distributions produced by the interference of diffracted wavefronts from multiple pupil configurations. Specifically, interference phenomena in the geometrical shadows of the Fresnel region close to the diffracting apertures are considered. The effects of multiple pupil geometry variations and preliminary impact of phase errors are considered. Finally, physical insights are offered for the phenomena of diffractive interference in the geometric shadow.

Calculation of sound insertion loss of a barrier by fresnel zone method

Abstract: In this paper the formulas are presented to estimate the sound pressure amplitude at the observationpoint behind a half-infinite sound barrier,especially in the shadow region.The barrier may be a thin screen,or awedge,or a wide barrier These formulas are based on the Huygens-Fresnel principle of diffraction and on theconcept of Fresnel half-period zone.By using these formulas a new method,Fresnel Zone Method,to calcu-late sound insertion loss of a barrier is obtained.The calculations agree well with the experimental results.

Effective radius for non-piston-like disc radiators

Abstract: The mechanisms which underline the location and magnitude of the axial pressure amplitude extreme have been investigated using Fresnel zones for a model of a disc transducer vibrating in a plate mode with a single node. It was found that the position of the last axial minimum gives an effective radius equal to the radius of the node. The magnitude of excitation of the anti-phased outer ring can be obtained from the ratio of the amplitude of the last axial minimum and last axial maximum

Double-sided grooved Fresnel lens for overhead projector

Abstract: This invention consists of a Fresnel lens (10) having focusing grooves (12,14) on both sides of a single element. The relative frequencies of the grooved surfaces are controlled such that Moire interference patterns between the two grooved surfaces (12,14) are reduced. Specifically, the frequency of the Fresnel elements (12) on one surface of the is at least four times that of the Fresnel elements (14) on the other surface and not a integral multiple thereof.

Wind velocity measurements by optical scintillations methods

Abstract: Scintillations-based optical techniques for the measurement of the atmospheric transverse average wind velocity are re-examined. Three different methods for the processing of the resultant time-lagged covariance function are compared to in-situ anemometer measurements. A correlation index of 0.89-0.95 is obtained between the optical and anemometer results and it tends to increasing with the measurement time constant. Some degradation in the accuracy of the optical methods is observed when the spacing between the detectors is either much smaller or much larger than the Fresnel zone [AL]1/2.

The Fresnel 'wave' train

Abstract: Most university optics courses include the theory of Fresnel diffraction and practical class experiments to demonstrate diffraction from straight edges and slits. While students find these relatively easy to set up, normally using a laser with a beam expander (Eaton and Wiseman 1976), they often find their interpretation using a phase-amplitude diagram considerably more difficult. As an aid to the visualisation of the calculation and as a quantitative method for the derivation of the amplitude of the Fresnel diffraction pattern from a slit, the authors have found 'N' gauge model railway analogue very useful.

Characteristics of optical components for soft x‐ray microscopy and x‐ray holography using an undulator radiation optical system (abstract)

Abstract: X‐ray Fresnel zone plates and transmission gratings, have been fabricated using fine‐focused electron‐beam lithography and Ta‐on‐SiN x‐ray mask fabrication technique. The optical components for x‐ray microscopy and x‐ray holography were evaluated in an undulator radiation system. Nanometer lithography using fine‐focused electron‐beam writing machines is now regarded as an important technology to create new devices on very small structures such as quantum wires or boxes and new scientific probe elements such as x‐ray optical components. A new fabrication process of Ta‐on‐SiN x‐ray mask1 for x‐ray optical components has been established. Tantalum is used for the x‐ray absorber, because of having approximately the same absorption coefficient as that of gold. A thin SiN film, which has a high transparency for soft x rays, acts as a membrane supporting the Ta‐absorbing patterns. The fabricated zone plates have an outermost zone width of 0.25 μm with up to 2 mm diameter. The pitch width of the transmission grat...

Adaptive focused beamforming

Abstract: Sonar (sound navigation ranging) is an apparatus that detects the presence and location of submerged objects (as a submarine) by means of sonic waves reflected back from or produced by an object.

Fresnel zone plate and aligning method using same

Abstract: PURPOSE:To dispense with the operation of an optical system for position alignment and to halve the number of Fresnel zone plates FZP, by using FZP wherein FZP having a focal distance f2(