Showing papers on "Fresnel zone published in 1986"

Scattering induced microwave scintillations from clear air and rain on earth space paths and the influence of antenna aperture

Abstract: The variance and spectrum of amplitude scintillations due to scattering in both turbulent clear air and rain, are investigated. Included are the important aspect of antenna aperture smoothing with special emphasis on earth-space paths and the equations derived are applicable to system design and remote sensing. A detailed comparison with published experimental results is carried out and the agreement found is good. Two approaches are described in detail: 1) the point receiver classical wave scattering results are modified to include aperture effects, 2) a scalar scattering cross-section approach is combined with the radar equation and the results derived are similar to those of 1). In addition, approach 2) includes the case of rain. Among the results found it is shown that because the scintillation intensity depends on the ratio between the antenna diameter and the diameter of the Fresnel zone in the turbulent region, low elevation paths counteract the tendency to smoothing by large earth station antennas and the scintillations observed remain large. Also pure scattering induced rain scintillations, even in the millimeter region, are in general reduced to an almost negligible level due to aperture smoothing even though for a theoretical point receiver they would be very intense. The time variability of rain attenuation and its polarization dependence as a source of apparent scintillations are also discussed.

Multiple wavelength linear zone plate alignment apparatus and method

Abstract: An optical alignment apparatus and method for a semiconductor lithography mask and wafer utilizes two monochromatic light sources of different wavelengths. The mask contains targets in the form of linear Fresnel zone plates and the wafer contains a reflecting grating. Incident illumination from the two light sources illuminates the mask targets and is reflected from the wafer gratings in various intensity depending on the physical characteristics of the wafer and mask layers and thicknesses and by the targets. A detector detects the strongest of the diffracted return beams from each of the monochromatic light sources and uses the strongest to align the targets and grating on the mask and wafer for more accurate printing of mask patterns on the wafer.

Proton-exchanged Fresnel lenses in Ti:LiNbO 3 waveguides

Abstract: Fresnel lenses were fabricated by the patterned proton-exchange technique in titanium-diffused lithium niobate waveguides. The large change in refractive index available with the proton exchange allows fabrication of a high-efficiency thin Fresnel lens. Lens characteristics of nearly diffraction-limited focus spot size and efficiency up to 70% were obtained. The use of the lens to construct an integrated-optic rf spectrum analyzer of 1-GHz bandwidth and 2-MHz resolution is also demonstrated.

Image reconstruction from partial Fresnel zone information.

Abstract: An iterative algorithm for reconstructing an image from partial Fresnel zone information is described. With the standard 4-F canonical optical processor, processing is done midway between the two lenses in the Fourier transform plane. While others have studied iterative methods of reconstruction from partial Fourier plane information, we have investigated methods of reconstructing an object from partial information in the Fresnel region of an optical processor. Iterative algorithms for reconstructing an object from either the phase or magnitude of the Fresnel zone transform are described. In the case of reconstructing an image from Fresnel zone magnitude, we obtain good images in fewer iterations at locations which are further from the Fourier plane. Reconstructing an image from the Fresnel zone phase is fairly insensitive to this shift out of the Fourier plane.

Focusing Characteristics of High-Efficiency Fresnel Zone Plate Fabricated by Deep Ultraviolet Lithography

Abstract: The feasibility of using photoresist Fresnel zone plates as micro-optic components was examined experimentally. Deep UV lithography was used to fabricate zone plates with submicron pitch, and nearly diffraction-limited spot formation and high efficiency were achieved. The direct collimation of a semiconductor laser beam was demonstrated.

Fresnel diffraction in an optical system containing lenses

Abstract: A convenient expression describing the location of Fresnel diffraction patterns when a diffracted spherical wave is focused by a lens is given. Experimental results confirm the predicted positions of 26 axial extrema corresponding to integer numbers of Fresnel half-period zones. Experimental radial intensity profiles are presented for some of these positions.

Optical alignment method

Abstract: PURPOSE: To increase an S/N ratio and to perform highly reliable alignment by eliminating the noise beam to a beam detector, by intermittently irradiating each alignment mark with laser beam in timings different from each other. CONSTITUTION: A plurality of diffraction lattices 11W13 on a wafer 1 corresponding to a plurality of the linear Fresnel zone plates 21W23 on a mask 2 are respectively irradiated with the laser beam from a laser beam source 31 through said Fresnel zone plates 21W23 and the beams obtained therefrom are respectively detected by beam detectors 71W73 to perform the relative alignment of the wafer 1 and the mask 2. The laser beam from the beam source 31 is inputted to the three-path optical switch 32 controlled by a control circuit 33 and output irradiation is performed in timings different from each other. By this method, the lowering in the S/N ratio of a detection signal caused by that the scattering beams from both of the wafer 1 and the mask 2 are incident to the beam detectors 71W73 not corresponding thereto is prevented and irradiation beam is made detectable only by the detectors 71W73 corresponding to each other to make highly reliable alignment possible. COPYRIGHT: (C)1988,JPO&Japio

A "tuned" Fresnel lens.

Abstract: We propose a technique to manufacture Fresnel lenses where the grooves are phase-synchronized at a given wavelength. This means that the light from different grooves will superpose coherently at the focal point at the specified wavelength. The focusing performance of such a “tuned” Fresnel lens will be better than that of ordinary Fresnel lenses by orders of magnitude and can, in principle, equal the performance of a conventional lens of the same diameter (diffraction limit). In optical communication systems, which use mostly narrowband light sources (lasers, LEDs), tuned Fresnel lenses may offer a lower cost alternative to conventional lenses without sacrificing focusing performance.

Laser resonator with high aspect ratio gain region and azimuthally symmetric Fresnel number

Abstract: An unstable optical resonator having a gain region that has an elliptic or other non-circular cross section still has the benefits of a total collimated cavity Fresnel number that is azimuthally symmetric by the combination of several cavity regions of azimuthally non-uniform Fresnel number of appropriate size.

Unstable optical cavity with modified fresnel zone

Abstract: An improved unstable optical cavity for optical amplifiers or laser oscillators is made effectively single mode by altering the central Fresnel zone of the back mirror in order to provide constructive interference at the plane of the output aperture.

Position detecting method

Abstract: PURPOSE:To eliminate the retreat of an objective lens after a mask and a wafer are aligned in an X-ray exposing device as well as to enable to obtain the detection signal of a high S/N by a method wherein a coherent light is illuminated on a mark from inside an exposed region in oblique direction toward the outside of the exposure region, and the focus of the diffracted light is formed in such a manner that it is directed to outside the exposure region. CONSTITUTION:The wafer 2 and the mask 3 attracted to a wafer chuck 1 are opposed each other across a microscopic gap (g) of 5-40mum. The circuit pattern on the mask 3 is transferred to the surface of the wafer 2 by projecting X-rays. The alignment marks 6 and 7 of a Fresnel zone are put on the surface of the wafer 2 and the mask 3 respectively. When a coherent light 8 is illuminated on said marks 6 and 7 from inside the exposing region toward outside the exposing region with the angle of oblique direction theta, the light 9 diffracted in the Fresnel zone is directed outside the exposing region with the angle of -theta, and a focus 10 is formed. An objective lens 11 is arranged by inclining at the angle of -theta for the purpose of detecting said focus. The focus of the diffracted light detected by the objective lens 11 passes through a light path 12, forms an image again on a sensor 13, and its position is detected by the sensor 13.

Fresnel Transforms And Optical Computing

Abstract: The Fresnel transform provides a means to implement circuit switching networks by using optical techniques. Since photons can cross paths without interaction, non-blocking configurations are easy to achieve. Furthermore, any arbitrary interconnections between two N-port systems can be configured; the network can be rapidly reconfigured as needed due to the dynamic nature of acousto-optic cells.

Optical Fibre Pressure Sensor Using a Deformable Lens

Abstract: A preliminary investigation has been undertaken into the use of deformable optical elements in optical fibre sensors for pressure measurement. The techniques employ wavelength modulation and simplified spectral detection to provide the output of the sensors. Experimental results are presented on sensors exploiting the chromatic aberration of deformable lenses and Fresnel zone plates. The temperature sensitivity of the sensors is considered.

Scanning heterodyne reconstruction of coded aperture images

Abstract: The reconstruction of coded aperture images using an optical scanning heterodyne processor is described for a class of apertures which can be synthesized by two beam interference. The analysis of Fresnel zone apertures indicates that a lateral and longitudinal (tomographic) resolution close to the theoretical limit is achievable. Experimental results of optical simulations confirm this assertion. Advantages of such technique include real-time operation and large multiplexing capability.

Reflective Optics for Soft X Rays I Grazing Incidence

Abstract: As discussed in Chapter 1, the reflectivities of single surfaces at normal or near-normal incidence for soft X rays are very small. High reflectivities from single surfaces are only obtained at grazing angles of incidence. This is because the refractive index of the reflecting medium is very close to, and slightly less than, that of the surrounding medium (vacuum)—the conditions under which total external reflection can occur.

Partially coherent radiation at x-ray wavelengths

Abstract: In this paper we discuss the properties of partially coherent radiation generated by X-ray lasers, undularcrrs, and laser produced plasmas. We discuss spatial and temporal coherence properties, experiments involving X-ray microscopy and microholography which benefit from varying degrees of coherence, and we illustrate radi'ative performance in terms of both coherent power and spectral brightness, for both peak and average values. Introduction In recent years we have seen a significant advance in the ability to generate coherent radiation at ever shorter wavelengths now extending throughout the ultraviolet and into the x-ray region of the electromagnetic spectrum. These are particularly interesting spectral regions for applications in many scientific and technological disciplines. Because the wavelength is short, the radiation can be used to both "see" and "write" patterns of small feature size. Thus one can form high spatial resolution x-ray microscopes and microprobes and can fabricate yet more powerful integrated circuits. The photon energy is particularly interesting as it coincides with the many atomic and molecular transition resonances which pervade this region of the spectrum. The new accessibility of this region, provided both high brightness sources and requisite x-ray optics are available, will permit the utilization of many exciting techniques. Element specific bio-dynamics, site specific photochemical processing, polarization sensitive scattering studies of chiral structures, element specific studies of surface state formation, and dynamical studies of thin film and lattice structure formation are, to name a few, fields which would benefit from the unique capabilities of elemental sensitivity and high space-time resolution. Coherence Requirements An example of an experimental technique which would benefit many of the above cited sciences is that of an x-ray microprobe. As illustrated in figure 1, a Fresnel zone plate might be used to concentrate radiation in a small Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1986627 C6-204 JOURNAL DE PHYSIQUE focal spot area. The radiation could be used to probe, stimulate or scan any of a variety of chemically, physically or biologically interesting systems. The size of the focal region is dependent upon both the spatial and temporal properties of the incident radiation. For spatially coherent radiation a focal spot diameter (waist) of 2.4Ar will be obtained with a zone plate of outer zone width Ar. Resolution, as defined by Rayleigh, would be 1.2Ar. A zone plate of outer zone width of 500 A would give a focal spot diameter of approximately 1200 A. To achieve this diffraction limited focusing it is necessary that the zone plate be perfect to a fraction of a wavelength, and that the radiation emanate from an uncertainty limited phase space characterized by 8-8 = A/2. If the radiation is characterized by a larger phase space, the resulting focal spot will be proportionally larger and the resolution proportionally degraded. The zone plate microprobe also requires a degree of temporal (longitudinal) coherence, albeit modest. In order to avoid blurring of the focal region by chromatic aberration, the radiation must possess a coherence length (distance over which interference effects are significant) Qc = A2/bA, at least as large as the coherence requirements of the zone plate, blA/2, where bl is the number of Fresnel zones. Generally this is a modest requirement: with bl = 500 and A -30 A, one requires Qc lpm. A somewhat more demanding experiment is that of off-axis x-ray microholography, as illustrated in figure 2. In this case the ZP does not form an image in the recording plahe, but rather it gathers the high frequency (large angle) scattered radiation (containing details of the smaller sample features) and directs it back toward the recording medium where it is encoded through interference with a plane or spherical reference wave generated by the nearby diffraction grating. The scattered radiation is thus heterodyned by the reference wave, with a carrier spatial frequency roughly that of the grating, allowing use of a lower resolution but more sensitive recorder (perhaps x-ray film) than would otherwise be possible. Both spatial and temporal coherence requirements are more demanding in the holographic case, requiring spatially coherent illumination over a field wider by some factor, and a temporal coherence length increased by that factor squared, e.g. if the grating extends laterally to a distance of five ZP radii, then the temporal coherence must be increased by a factor of twenty-five. Thus one would require full spatial coherence and a longitudinal coherence of 20 pm. Radiation Sources The generation of partially coherent radiation, combined with requisite spatial and temporal filtering, can be achieved in several ways. Figures 3-5 illustrate an atomic laser, a magnetic undulator, and a laser-produced, hot-dense plasma emitting x-rays into 2s steradians. All three can generate radiation at XW wavelengths, and perhaps it can be said that all are partially coherent certainly all could be used as the source of radiation in figures 1 and 2. The differences are the degree of coherence, determining the amount of spatial and temporal filtering required for a particular application; the average a?d peak power produced; and the shortness of the wavelength and its nearness to the atomic and molecular resonances of interest. Radiative Performance In figures 6-8 we show generated coherent power and spectral brightness, for both average and peak values, and for a variety of spectral widths (coherence lengths). In the estimates of coherent power, only that portion of the radiation within d-8 = A/2 is accepted, such that full spatial coherence would result. In addition, perfect optics are assumed no aberrations, 100% efficiency. The need for several illustrations is due to the wide variety of applications one can envision, some requiring minimal coherence, others requiring substantial coherence. Upon inspection one readily sees that each of the radiation sources has its own advantages. References 1. D.L. Hatthews et al., Phys. Rev. Letters, 54, 110, 1985; M.D. Rosen et al., Phys Rev. Letters, 54, 106, 1985. 2. D.T. Attwood, K-J. Kim, K. Halbach, and H.R. Howells, "Undulators as a Primary Source of Coherent X-rays", paper presented at the International Conference on Insertion Devices for Synchrotron Sources, October 1985; also published as Lawrence Berkeley Laboratory PUB-20569, 1985. 3. Recent (June, 1986) undulator experiments are reported by H. Rarbaek, Brookhaven National Laboratory, Upton. New York. 4. D.W. Phillion, E.H. Campbell et al.. to be published; D.T. Attwood, N.M. Ceglio, E.H. Campbell, J.T. Larson, D.H. Hatthews, and S.L. Lane, "Compression Heasurements in Laser-Driven Implosion Experiments", Laser Interaction and Related Plasma Phenomenon, (Plenum, New York, 1981) eds. H.J. Schwarz. H. Hora, M.J. Lubin, and B. Yaakobi; B. Yaakobi et al., Optics Communications, 33, 196, 1981. 5. Nasif Iskander and Nadine Wang, Optical Society of America, Topical Conference on Short Wavelength Coherent Radiation. Honterey. CA, April 1986. zones Resolution = 1.2 FA = 1.2 Ar D = 4NAr Figure 1. An x-ray microprobe based on use of a Presnel zone plate. Spatially coherent radiation is focused to the smallest possible focal spot, of diameter 2.4Ar. Longitudinal (temporal) coherence equal to N W 2 is required to avoid chromatic defocusing effects, where N is the number of zones. Thus both temporal and spatial coherence are required.

Peak accelerations from subshear and supershear radiation of kinematic dislocation models

Abstract: The field of accelerations of a kinematic fault-model are evaluated in terms of fundamental interference-integrals that depend upon the source-observer geometry and the various spatial and 'temporal source elements. The dependence of the accelerations at various distances r from the fault's center, on the fault's major dimension L and the radiation's wavelength λ are scaled to the three dimensionless 'regionalization-indices': 2πr/λ, 2L2/λr and 0.62 × (L/r) √L/λ. These determine the limits of the far-field, the outer Fresnel-zone and the inner Fresnel-zone respectively. The interference integrals are then evaluated through the stationary-phase approximation and the Fresnel approximation both in the time and frequency domains. In the Fresnel zone they are expressed in terms of the Lommel functions of two variables. The ensuing acceleration field is shown to depend strongly on the shear Mach-number. In subshear-rupture, the acceleration in the near-fault and Fresnel zones decreases exponentially in a direction normal to the fault. In supershear-rupture the acceleration is a Mach-wave that propagates without attenuation along the Mach-lines. The theoretical scaling law for the acceleration in each region is determined. We assert: (1) peak accelerations in the near-fault zone are essentially independent of the earthquake's magnitude; (2) peak accelerations in the near-fault and Fresnel zones are proportional to the particle velocity on the fault; (3) accelerations in the near-fault and Fresnel zones are determined by the radiation from the nearest fault-segment. This explains the elliptical shape of isoseismals, which are locii of equidistant points from the fault.

Extended marine arrays versus simulated extended arrays

Abstract: Two factors are responsible for the fact that an extended marine source array performs better than a point source: 1. a higher degree of transmission of the radiated seismic energy through the water-sediment interface providing a better penetration; 2. filtering effects. The higher degree of transmission is due to: (a) the directivity of extended sources, (b) the lower reflection coefficient at the water-sediment interface for seismic waves radiated from an extended source array than for spherical seismic waves radiated from a point source, (c) the lower amplitude decay of the pulses from an extended source than from a point source. In addition, signature characteristic of an extended source array and Fresnel zone of waves generated by such a source differ from those corresponding to a point source. The propagating wavelet radiated from a point source array may not be, in a sedimentary sequence below the sea-floor, the linear combination of wavelets emitted from point sources. In such cases, there is a noticeable difference between the performance of a field-implemented source array and that of the corresponding simulated source array. The performances of the field-implemented and simulated extended receiver arrays can be identical if the recording system is adequate and the processing technique appropriate.

Plane fresnel lens

Abstract: PURPOSE:To draw a bright lens of a small F-number even if an electron beam having a large diameter is used by disposing alternately Fresnel zones on the right and left of the virtual center line intersecting orthogonally with the propagating direction of the light beam. CONSTITUTION:The lens part 31 having a high refractive index is drawn by irradiation of an electron beam to part of amorphous arsenic sulfide 13 of a plane Fresnel lens. The lens parts 31 are alternately arranged on the right and left of the virtual center line 32 intersecting orthogonally with the propagating direction of the light beam. The overlap of the two adjacent Fresnel zones is thus obviated and the cross width amin of the zones is made smaller. Since the F-number is proportional to amin, the F-number can be diminished by making the same smaller. The F-number is thus made 1.2 and the drawing of the bright Fresnel lens is made possible even if 0.3mu electron beam is used.

Dispersive characteristics of one-dimensional Fresnel zone plates measured using synchrotron radiation

Abstract: This paper presents the dispersive characteristics of a Ta film one-dimensional Fresnel zone plate (FZP) measured using synchrotron radiation as a light source. Spectral spatial distributions of the FZP linear monochromator output beam are recorded on an X-ray film. The observed distributions are well explained by the FZP's chromatic aberration. The spectral bandwidth of the monochromator output beam decreases proportional to the slit width and saturates at approximately the value limited by the size of the focused image of the synchrotron radiation source.

Fresnel region imaging with a linear array

Abstract: This paper presents a complete solution to the analysis and synthesis of both angular and axial field patterns in the Fresnel region of linear arrays, and applies the theory to Fresnel region imaging. Both the angular and axial field patterns are shown to be Fourier transforms of the suitably modified aperture distribution, and can therefore also be synthesized by the inverse Fourier transform.

A passive process for the variation of the phases in the fresnel zones

Abstract: The process consists in that electric bodies, transparent to the electromagnetic waves, are introduced into the paths thereof, so as to cover different Fresnel zones and thereby producing phase variations of the waves passing separately through each zone.