Showing papers on "Fresnel zone published in 1999"
TL;DR: In this article, a heuristic model of irradiance fluctuations for a propagating optical wave in a weakly inhomogeneous medium is developed under the assumption that small-scale irradiance fluctuation fluctuations are modulated by large-scale fluctuations of the wave.
Abstract: A heuristic model of irradiance fluctuations for a propagating optical wave in a weakly inhomogeneous medium is developed under the assumption that small-scale irradiance fluctuations are modulated by large-scale irradiance fluctuations of the wave. The upper bound for small turbulent cells is defined by the smallest cell size between the Fresnel zone and the transverse spatial coherence radius of the optical wave. A lower bound for large turbulent cells is defined by the largest cell size between the Fresnel zone and the scattering disk. In moderate-to-strong irradiance fluctuations, cell sizes between those defined by the spatial coherence radius and the scattering disk are eliminated through spatial-frequency filtering as a consequence of the propagation process. The resulting scintillation index from this theory has the form σI2=σx2+σy2+σx2σy2, where σx2 denotes large-scale scintillation and σy2 denotes small-scale scintillation. By means of a modification of the Rytov method that incorporates an amplitude spatial-frequency filter function under strong-fluctuation conditions, tractable expressions are developed for the scintillation index of a plane wave and a spherical wave that are valid under moderate-to-strong irradiance fluctuations. In many cases the models also compare well with conventional results in weak-fluctuation regimes. Inner-scale effects are taken into account by use of a modified atmospheric spectrum that exhibits a bump at large spatial frequencies. Quantitative values predicted by these models agree well with experimental and simulation data previously published. In addition to the scintillation index, expressions are also developed for the irradiance covariance function of a plane wave and a spherical wave, both of which have the form BI(ρ)=Bx(ρ)+By(ρ)+Bx(ρ)By(ρ), where Bx(ρ) is the covariance function associated with large-scale fluctuations and By(ρ) is the covariance function associated with small-scale fluctuations. In strong turbulence the derived covariance shows the characteristic two-scale behavior, in which the correlation length is determined by the spatial coherence radius of the field and the width of the long residual correlation tail is determined by the scattering disk.
331 citations
TL;DR: In this article, the authors report the fabrication of high-efficiency, high-contrast gold and nickel multistep (quaternary) Fresnel zone plates using electron beam lithography.
Abstract: The development of high brilliance X-ray sources coupled with advances in manufacturing technologies has led to significant improvements in submicrometre probes for spectroscopy, diffraction and imaging applications. The generation of a small beam spot size is commonly based on three principles1: total reflection (as used in optical elements involving mirrors or capillaries), refraction (such as in refractive lenses2) and diffraction. The latter effect is employed in Bragg–Fresnel or Soret lenses, commonly known as Fresnel zone plate lenses. These lenses currently give the best spatial resolution, but are traditionally limited to rather soft X-rays—at high energies, their use is still limited by their efficiency. Here we report the fabrication of high-efficiency, high-contrast gold and nickel multistep (quaternary) Fresnel zone plates using electron beam lithography. We achieve a maximum efficiency of 55% for the nickel plate at 7 keV. In addition to their high efficiency, the lenses offer the advantages of low background signal and effective reduction of unwanted diffraction orders. We anticipate that these lenses should have a significant impact on techniques such as microscopy3, micro-fluorescence4 and micro-diffraction5, which require medium resolution (500–100 nm) and high flux at fixed energies.
274 citations
TL;DR: Three-dimensional incoherent primary sources can be reconstructed from finite-aperture Fresnel-zone mutual intensity measurements by means of coordinate and Fourier transformation and the spatial bandpass and impulse response for three-dimensional imaging are derived.
Abstract: We show that three-dimensional incoherent primary sources can be reconstructed from finite-aperture Fresnel-zone mutual intensity measurements by means of coordinate and Fourier transformation. The spatial bandpass and impulse response for three-dimensional imaging that result from use of this approach are derived. The transverse and longitudinal resolutions are evaluated as functions of aperture size and source distance. The longitudinal resolution of three-dimensional coherence imaging falls inversely with the square of the source distance in both the Fresnel and Fraunhofer zones. We experimentally measure the three-dimensional point-spread function by using a rotational shear interferometer.
69 citations
TL;DR: In this article, a method for line width control in electron beam lithography is presented, which is especially suited for the manufacture of diffractive optical elements, by defocusing the spot of the electron beam writer.
66 citations
TL;DR: X-ray microscopy has seen great growth in the last two decades in the number and types of operating instruments as well as their capabilities as mentioned in this paper, which is due to two developments: the development of high-brightness second-and third-generation synchrotron light sources that can be used with small-aperture optics.
Abstract: X-ray microscopy has the capability of looking into normally opaque samples with high resolution. X rays are sensitive to elemental, structural, and chemical content and thus can provide microscopic maps of the composition and structure of a sample. X-ray microscopy has seen great growth in the last two decades in the number and types of operating instruments as well as their capabilities. This growth is due to two developments. The first is the development of high-brightness second- and third-generation synchrotron light sources that can be used with small-aperture optics. The second is a revolution in x-ray optics. In addition to the extension of commonly used visible optics, such as Fresnel zone plates and multilayer mirrors, into the x-ray regime, there has also been a dramatic improvement in grazing-incidence optics fabrication. In the range up to a few keV, Fresnel zone plates offer the highest resolution, which is below 100 nm in several instruments. Recent developments in fabrication may lead to t...
51 citations
TL;DR: In this paper, the authors analyzed SKS/SKKS waveforms recorded by permanent, broadband stations in Australia and found a lack of birefringence: Signals in general are absent on the transverse (T) component of high-quality data over a wide range of back-azimuths.
35 citations
TL;DR: A recursive algorithm to implement phase retrieval from two intensities in the Fresnel transform domain is proposed that can significantly simplify computational manipulations and does not need an initial phase value compared with conventional iterative algorithms.
Abstract: We first discuss the discrete Fresnel transform and present some essential properties. We then propose a recursive algorithm to implement phase retrieval from two intensities in the Fresnel transform domain. This approach can significantly simplify computational manipulations and does not need an initial phase value compared with conventional iterative algorithms. Simulation results show that this approach can successfully recover the phase from two intensities.
35 citations
11 Jul 1999
TL;DR: In this article, the authors summarized some of the growth in technology for Fresnel zone plate antennas in the microwave and millimeter-wave regions and gave a description of the earliest developments of Fresnel plate antennas at optical frequencies.
Abstract: This paper summarizes some of the growth in technology for Fresnel zone plate antennas in the microwave and millimeter-wave regions. A description is given of the earliest developments of Fresnel zone plates at optical frequencies. Most of the material concerns previous results obtained for microwaves and millimeter-waves.
30 citations
TL;DR: An optical correlator that can operate with totally incoherent light that exploits available achromatic lenses and Fresnel zone plates was designed, built, and tested experimentally, and revealed that detectable correlation peaks can be obtained withotally incoherent white light.
Abstract: An optical correlator that can operate with totally incoherent light is presented. Such a correlator can be designed to compensate completely for the inherent chromatic aberrations by resorting to elements with specialized, possibly impractical, dispersion characteristics. Nevertheless, a practical configuration that exploits available achromatic lenses and Fresnel zone plates was designed, built, and tested experimentally. The results reveal that detectable correlation peaks can be obtained with totally incoherent white light. The designs, experimental procedures, and results are presented.
26 citations
TL;DR: In this paper, a velocity anomaly is introduced in a homogeneous medium and the presence of the velocity anomaly breaks the wavefront into two main parts, the first part which travels through the anomaly, corresponds to the specular ray and gives rise to an event which is called the ray event since it can be predicted by standard ray tracing techniques.
Abstract: For impedance, velocity resolution depends on Fresnel zone considerations. A change of velocity can be distinguished only if its size is greater than the Fresnel zone. This is demonstrated on synthesized examples where a single velocity anomaly is introduced in a homogeneous medium. (Although unrealistic, this model was designed to exhibit the physical phenomenon in its simplest configuration.) The presence of the velocity anomaly breaks the wavefront into two main parts. The first part, which travels through the anomaly, corresponds to the specular ray and gives rise to an event which we call the ray event since it can be predicted by standard ray‐tracing techniques. The second, which emanates from outside the anomaly, does not correspond to a ray event. Therefore, we call it the nonray event. It travels at the speed of the background medium. The relative amplitude of the two events depends upon the size of the anomaly compared to the size of the Fresnel zone. When the anomaly is larger than the Fresnel ...
22 citations
01 Sep 1999
TL;DR: The article presents a generalized method, using the Fourier transform, for computing and graphically displaying the Fresnel diffraction intensity pattern for any planar aperture, and can obtain the entire pattern at once, in contrast to the standard methods' point-by-point evaluation process.
Abstract: The study of Fresnel diffraction is an integral part of any course in physical optics. Fresnel diffraction occurs when an aperture is illuminated with coherent light and the resulting diffraction pattern appears on a screen, a finite distance from the aperture. In general, the techniques found in standard optics texts' to compute the intensity of the diffraction pattern as a function of position on the screen are limited and aperture-specific. However, as texts on modern optics show, we can formulate Fresnel diffraction in terms of the Fourier transform of a modified aperture function. The article presents a generalized method, using the Fourier transform, for computing and graphically displaying the Fresnel diffraction intensity pattern for any planar aperture. With the advent of the PC and packaged mathematical software containing the fast Fourier transform algorithm, it is now possible to perform these calculations with minimum effort. The advantage of this method is that you can obtain the entire pattern at once, in contrast to the standard methods' point-by-point evaluation process.
TL;DR: In this paper, a complex-valued sensitivity kernel is proposed for the representation of underside reflections through a Kirchhoff integral formulation, which accounts for the varying sensitivity of the waveforms to discontinuity structure over the Fresnel zone.
Abstract: This paper presents a method to invert underside-reflection (P(d)P or S(d)S arrivals) data for lateral depth variations of upper-mantle discontinuities, combining traveltime and amplitude data. The method greatly improves the resolution of small-scale undulations obtained by existing imaging methods and does not suffer from the long-wavelength biases that are likely to be present in currently available models. Existing inversion methods account for the large size of the Fresnel zone of underside reflections, but not for its complexity, arising from the mini-max traveltime nature of PP- and SS-related waves. This neglect results in long-wavelength artefacts from small-scale undulations of the discontinuities, obscurring true long-wavelength depth variations. The inversion method presented in this paper uses a complex-valued sensitivity kernel, derived from the representation of underside reflections through a Kirchhoff integral formulation. The sensitivity kernel accounts for the varying sensitivity of the waveforms to discontinuity structure over the Fresnel zone. The method is applied to a large, synthetic data set. The data set consists of P(d)P amplitudes and traveltimes. The results show that the new inversion method resolves depth variations on a lateral scale that is smaller than the size of the Fresnel zone of individual underside reflections (but larger than the dominant wavelength), retaining the resolution of large-scale variations. The results presented here suggest that the discontinuity depth variations induced by slab penetration of the 670 discontinuity could be resolved by current broad-band P670P data sets.
TL;DR: In this paper, a new analytical method for the prediction of road traffic noise propagation (called MAPB in French) is presented, which answers the need of a simple calculation tool usable in the new standard that is being elaborated in France.
TL;DR: In this article, a more reasonable zoning rule is proposed to further increase the antenna gain by about 1 dB, where the distance from two edges of each zone to a common focus is progressively increased with a half-wavelength step.
Abstract: In the traditional zoning rule of the Fresnel zone plate (FZP), the distance from two edges of each zone to a common focus is progressively increased with a half-wavelength step. In this paper, a more reasonable zoning rule is proposed to further increase the antenna gain by about 1 dB. ©1999 John Wiley & Sons, Inc. Microwave Opt Technol Lett 23: 69–73, 1999.
TL;DR: In this paper, the second generation of grazing-incidence-phase Fresnel zone plates is presented and the term GIDFL is proposed to describe the diffraction properties of these lenses and allows one to calculate the focal spot intensity.
TL;DR: In this paper, the Rayleigh-Sommerfeld and Kirchhoff solutions to the diffraction of a converging spherical (or cylindrical) wave are expressed in terms of a series of derivatives of the field estimate that follows from the Fresnel approximation.
Abstract: By extension of the transitional operator method developed by Wunsche, the Rayleigh–Sommerfeld and Kirchhoff solutions to the diffraction of a converging spherical (or cylindrical) wave are expressed in terms of a series of derivatives of the field estimate that follows from the Fresnel approximation. This result allows a systematic assessment of the error associated with the paraxial wave model for focused fields and offers simple corrections to this model. In particular, for simple diffracting masks, the Fresnel approximation leads to estimates of the field that have a relative error near focus that is of the order of one on the square of the f-number. The number of significant digits in the field estimate is shown to be doubled by retaining just the first of the series of corrections derived here.
TL;DR: In this paper, a brushless linear motor and a high resolution linear encoder are integrated into an air slide table for photo-mask pattern-making, which is applied to a laser beam writer, which must be capable of rendering minute and precise patterns for photo masking equipment.
Abstract: This paper reports on the development of a unique, high precision linear motor integrated air slide table for precise positioning and its application to laser beam writers for photo-mask pattern-making. The air slide table takes advantage of the balance between the air bearing’s levitating and magnetic forces. A brushless linear motor and a high resolution linear encoder are integrated into the table. The unique construction of the device results in a very compact package with excellent accuracy. The basic characteristics of the air slide table are evaluated. The device is applied to a laser beam writer, which must be capable of rendering minute and precise patterns for photo-masking equipment. Examples are given including optical devices such as wave guides and Fresnel zone plates which were fabricated and evaluated. Experimental data is given to show that the Fresnel zone plate fabricated here can be used to focus a laser beam to the theoretical limit, just like a standard refractive lens.
01 Oct 1999
11 Jul 1999
TL;DR: In this paper, the basic outcomes of the several years of research on the Fresnel zone plate lenses and antennas accomplished at the Eindhoven University of Technology (EUT) are summarized.
Abstract: The paper summarizes the basic outcomes of the several years of research on the Fresnel zone plate lenses and antennas accomplished at the Eindhoven University of Technology (EUT). Added are also some results obtained at the Technical University of Vama (TUV) as an extension of the joint work on the subject between the EUT and the TUV initiated under a CEC/COST research contract. In this paper, we pay attention to the transmission Fresnel zone plates and Fresnel zone plate antennas only.
12 Nov 1999
TL;DR: In this paper, phase correcting Fresnel zone plate antenna can provide performance superior to a lens or, in some cases, a paraboloid antenna, particularly at millimeter-wave or sub- millimeter wavelengths.
Abstract: A well-designed phase correcting Fresnel zone plate antenna can provide performance superior to a lens or, in some cases, a paraboloid antenna, particularly at millimeter wavelengths. This paper discusses design considerations and includes approaches to give improved characteristics, such as greater efficiency or higher gain. The approaches include the use of quarter-wave or better correction, thickness designs that permit the central zone and other zones to be air dielectric (for lower losses), and the use of low dielectric constant materials to reduce surface reflections and multiple reflections. At higher millimeter-wave or sub- millimeter wavelengths low loss materials are important. More sophisticated zoning is described, as well as the use of a compromise thickness to compensate for the fact that refraction of waves at the surfaces causes the path lengths through the zone plate to be different at different angles of incidence. Multiple-band zone plates are discussed.
TL;DR: In this article, the X-ray magnetic dichroism (X-MCD) was used as huge contrast mechanism in combination with a transmission Xray microscope based on Fresnel zone plates thus providing a lateral resolution down to 30nm.
Abstract: The X-ray magnetic dichroism (X-MCD) which exhibits at L-edges of transition metals and M-edges in Rare Earth systems values up to 25% can be used as huge contrast mechanism in combination with a transmission X-ray microscope based on Fresnel zone plates thus providing a lateral resolution down to 30nm. Trial results demonstrating the features of this new technique, like the recording in varying external fields, the relation to local magnetic moments, etc. will be presented and demonstrate the applicability to study the magnetic domain structure in current technical relevant systems, like ultrahigh density storage media, multilayers for GMR applications and nanostructures for MRAM technology.
07 Jun 1999
TL;DR: In this article, the authors proposed a fast algorithm for computing traveltimes like FD techniques, but this algorithm does not yield amplitudes and they usually must be calculated by the slower ray methods (dynamic ray tracing).
Abstract: Geometrical spreading plays an important role for various applications, e.g. true amplitude migration, estimation of Fresnel zones, divergence corrections. Unfortunately, fast algorithms for computing traveltimes like FD techniques do not yield amplitudes. They usually must be calculated by the slower ray methods (dynamic ray tracing).
11 Jul 1999
TL;DR: In this article, focusing properties of conducting and dielectric cylinders on the basis of the Fresnel zone principle were discussed, and the radiation patterns when the cylinders were excited with an isotropic source were evaluated using the boundary element method.
Abstract: the In this article, we discuss focusing properties of conducting and dielectric cylinders on the basis of the Fresnel zone principle. The radiation patterns when the cylinders are excited with an isotropic source are evaluated using the boundary element method. Helix antennas combined with a Fresnel zone plate are also reported. Enhanced gain characteristics are experimentally demonstrated.
TL;DR: In this paper, the effects of transverse coherence in time domain nuclear resonant scattering experiments using synchrotron radiation were discussed and the importance of source and detector sizes, as well as the Fresnel zone size of the sample are described.
Abstract: We discuss the effects of transverse coherence in time domain nuclear resonant scattering experiments using synchrotron radiation. The importance of source and detector sizes, as well as the Fresnel zone size of the sample are described. These effects are demonstrated in experiments using a rotating stainless-steel foil [1]. The emphasis of the text is to provide simple physical explanations while mathematical details are discussed in the appendix.
TL;DR: In this paper, a family of multi-layer Fresnel Zone Plate (FZP) lenses is proposed to enhance the aperture efficiency, and suppress the backward radiation, in order to analyze the field distribution in the focal region of the lens, an improved full wave analysis based on vector Hankel transform and spectral domain immittance matrix is developed.
Abstract: A family of multi-layer Fresnel Zone Plate (FZP) lenses is proposed to enhance the aperture efficiency, and suppress the backward radiation. In order to analyze the field distribution in the focal region of the lens, an improved full-wave analysis based on vector Hankel transform and spectral domain immittance matrix is developed. Various fundamental properties of FZP lens are given, these properties will provide guidance for designing a FZP lens antenna.
TL;DR: In this article, the authors present estimates of the Fresnel zone diameter for the axial magma chamber lens along the southern and northern East Pacific Rise and compare them to the magma lens widths derived from migrated seismic sections.
Abstract: We present estimates of the Fresnel zone diameter for the axial magma chamber lens along the southern and northern East Pacific Rise and compare them to the magma lens widths derived from migrated seismic sections. The mean values of that diameter are 996m and 1052m and the mean values of the magma lens width are 680m and 1056m respectively. Most individual estimates of the magma lens width fall below the Fresnel zone diameter. Similar results are presented for three other mid-ocean ridges. The registered signal is therefore a mix of responses from the magma sill and the encasing rock and lateral resolution is not achieved. We conclude that data analysis procedures that assume a laterally homogeneous Earth, cannot provide reliable estimates of the magma lens physical properties, including whether it is liquid or not.
01 Jan 1999
TL;DR: In this paper, the design of optical diffusers for the generation of flat-top intensity distributions, as required for 248 nm or 193 nm excimerlaser applications, is discussed.
Abstract: In this chapter we discuss the design of optical diffusers for the generation of flat-top intensity distributions, as required for 248 nm or 193 nm excimerlaser applications [4,5]. We investigate the generation of far-field distributions with various shapes, uniform intensity and high efficiency.
27 Aug 1999
TL;DR: In this article, a computer analysis of frequency and dynamic characteristics of the Bragg cell with different types of interdigital electro-acoustic transducers was carried out and the temperature and radiation effects upon the interference phenomena in the bragg cell were investigated.
Abstract: The several dozen versions of waveguide acousto-optical devices (WAOD) are used as components of photonic system. The quality of the WAOD essentially determines the limiting parameters of photonic system. The characteristics of WAOD are defined by the Bragg cell and the lens system. A particular emphasis was laid upon computer analysis of frequency and dynamic characteristics of Bragg cell with different types of interdigital electro-acoustic transducer. The temperature and radiation effects upon the interference phenomena in the Bragg cell were investigated. The planar lens system with high numerical aperture should be used for a high resolution and dynamic range (DR). To increase the numerical aperture the optical system included several planar refractive lenses have to be used. We have been design the optical systems included planar refractive lenses and modified topology Fresnel lens. Therefore the elements of Fresnel lens can be of different thickness and to several Fresnel zones. The surface of the eye's pupil should be aplanatic lens design. In the case of WAOD the DR for two resoluted signals is defined by a laser optical beam aperture function, its frequency spectrum, optical losses, displacement and geometry of a CCD detector array. In the case the computer simulation is shown that the DR depend on autocorrelation length for Rayleigh and Mie scattering, scattering on scratches. The scratches give local maximums in scattering function.
26 Mar 1999
TL;DR: In this paper, an electrically controllable dual focal point (DFP) lens was fabricated by combining an electro-optic (E-O) material with the Fresnel zone-plate (FZP) lens, in which numerous transparent (ITO) electrodes are evaporated in the form of the FZP on a PLZT ceramic E-O plate.
Abstract: Setting an electrically controllable dual focal-point (DFP) lens into the optical resonator of a laser, we can readily modulate the output power of the optical beam with a relatively low voltage. The DFP lens is fabricated by combining an electro-optic (E-O) material with the Fresnel zone-plate (FZP) lens, in which numerous transparent (ITO) electrodes are evaporated in the form of the Fresnel zone- plate (FZP) on a PLZT ceramic E-O plate to compose a dual focal-point lens with and without an applied voltage. In addition, the PLZT (La/Zr/Ti equals 9/65/35) ceramic used here as an E-O material represents a quadratic E-O effect. Inserting this DFP E-O lens inside the optical resonator of an He-Ne 3.39 mm laser on trial, the fundamental modulation characteristics are investigated. As a result, about 15.5% modulation degree was obtained with applying the rf (2 kHz) voltage of 13.5 V p under a certain bias. The operational principle is experimentally demonstrated together with theoretical discussions.
TL;DR: In this paper, the diffraction produced by a single binary (in amplitude) rectangular slit on two interfering optical beams with the Rayleigh-Sommerfeld formula in the Fresnel approximation was analyzed.
Abstract: In this work we analyse the diffraction produced by a single binary (in amplitude) rectangular slit on two interfering optical beams with the Rayleigh—Sommerfeld formula in the Fresnel approximation. The beams are monochromatic and mutually coherent. The results presented correspond to the case in which one bright fringe passes through the slit with the field amplitude at the edges of the slit being equal to zero. As a result, diffraction effects are considerably diminished and the diffracted beam behaves, approximately, as pseudo-non-diffracting. The numerical analysis is in agreement with the experiment.