Showing papers on "Zone plate published in 1992"

Generation of optical phase singularities by computer-generated holograms.

Abstract: Laser beams that contain phase singularities can be generated with computer-generated holograms, which in the simplest case have the form of spiral Fresnel zone plates.

High-Resolution Imaging by Fourier Transform X-ray Holography.

Abstract: Fourier transform x-ray holography has been used to image gold test objects with submicrometer structure, resolving features as small as 60 nanometers. The hologram-recording instrument uses coherent 3.4-nanometer radiation from the soft x-ray undulator beamline X1A at the National Synchrotron Light Source. The specimen to be imaged is placed near the first-order focal spot produced by a Fresnel zone plate; the other orders, chiefly the zeroth, illuminate the specimen. The wave scattered by the specimen interferes with the spherical reference wave from the focal spot, forming a hologram with fringes of low spatial frequency. The hologram is recorded in digital form by a charge-coupled device camera, and the specimen image is obtained by numerical reconstruction.

Use of fresnel zone plates for material processing

Abstract: The apparatus for machining and material processing includes an excimer laser and a Fresnel zone plate array (FZP) positioned parallel to the workpiece, with the distance between the FZP and the workpiece being the focal length of the FZP. For each hole to be formed on the workpiece a corresponding Fresnel zone is patterned onto the FZP. Each Fresnel zone may be patterned directly centered over the desired hole location or in high density patterns it may be located off-center from the hole with deflection being accomplished by the formation of finer circular arcs on the side of the Fresnel zone opposite the desired direction of deflection. A beam scanner is included to provide a more uniform illumination of the FZP by the laser beam. The scanning eliminates non-uniformity of intensity. The alignment mechanism uses a helium-neon laser, the beam from which is projected onto a surface relief grating on the workpiece. The reflected light from the surface relief grating is filtered to create interference fringes which, when aligned, provide maximum light intensity projected through a transmission grating on the Fresnel zone plate.

Diffraction by a circular aperture: a generalization of Fresnel diffraction theory

Abstract: A generalization of the Fresnel approximation in diffraction theory is proposed. The phase term in the diffraction integral is approximated by a paraboloidal variation, not by a binomial expansion but rather by a matching at the critical points in asymptotic evaluation of the integral. The method provides a correction to the optical coordinates of the Fresnel diffraction theory that extends its region of validity. It is applied to diffraction by a circular aperture of a plane wave or focused beam, including effects caused by a large numerical aperture, finite Fresnel number, off-axis illumination, and the presence of aberrations. The method may also be used with other geometries: It is readily applied to cylindrical focusing.

Hard x‐ray phase zone plate fabricated by lithographic techniques

Abstract: A Fresnel phase zone plate with an unprecedented focusing efficiency of 33% was fabricated using an x‐ray lithographic technique and was tested using synchrotron x rays. Contributions by the zeroth‐order x ray to the focus were minimal. Spatial resolution in the micrometer range was achieved. The measured spot size was dominated by geometric demagnification of the source. It should be possible to obtain submicrometer resolution by aperturing the source. Experimental results of focusing efficiency measurements, intensity distribution at the focal plane, and spatial resolution tests are reported.

Diffraction and Focusing of Spectral Energy in Multiphoton Processes

Abstract: We demonstrate an analogy between a two-photon process driven by a chirped pulse and Fresnel diffraction from a slit: in both situations interference between different ``paths'' leading to the same ``final state'' determines the resulting ``diffraction pattern.'' On the basis of this analogy, a spectral Fresnel zone plate was designed for ``focusing of spectral energy'': at the two-photon level the spectral energy can be concentrated in an effective bandwidth that is much smaller than the bandwidth of the original excitation pulse. To show this effect, two experiments were performed with femtosecond laser pulses with a well-controlled power spectrum and chirp: frequency doubling in a nonlinear crystal and two-photon excitation of Rydberg states in rubidium.

Gabor zone plate with binary transmittance values.

Abstract: A methodology is presented for producing a Gabor zone plate by using a binary transmittance function that is both radially and azimuthally distributed on the surface of the plate. The measured optical properties of such a plate are shown to be in agreement with those of the idealized Gabor plate that possesses a radially sinusoidal transmittance function.

Demonstration of x-ray microscopy with an x-ray laser operating near the carbon K edge

Abstract: High-brightness and short-pulse-width (~200 ps) x-ray lasers offer biologists the possibility of high-resolution three-dimensional imaging of specimens in an aqueous environment without the blurring effects associated with natural motions. As a first step toward developing the capabilities of this type of x-ray microscopy we have used a tantalum x-ray laser (λ = 4.483 nm) together with an x-ray zone plate lens to image a test pattern. The observed image shows a detector-limited resolution of approximately 75 nm and paves the way to three-dimensional biological imaging with high spatial resolution (20–30 nm).

A millimeter-wave integrated-circuit antenna based on the Fresnel zone plate

Abstract: A new type of millimeter-wave integrated-circuit antenna is based on a quasi-optical design is investigated. It consists of a Fresnel zone plate on one side of a dielectric substrate and a resonant strip dipole antenna at the focus of the zone plate on the opposite side of the substrate. All of the components are made using simple integrated-circuit fabrication techniques: thin-film metal depositions on planar dielectric substrates. Another features of this design is the short focal length of the zone plate; the focal length/diameter (f/d) for the zone plates studied ranges from 0.1 to 0.5. The antennas described are for a frequency of 230 GHz ( lambda /sub 0/=1.3 mm); however, the design is easily scaled to other millimeter-wave or submillimeter-wave frequencies. Measured results are reported for four different focal length zone plates. Moderate gains, above 20 dB, are obtained. A theory is developed which predicts the on-axis gain, beamwidth, and sidelobe levels. Design graphs are given to aid in the selection of the geometrical parameters to achieve a desired gain from the integrated-circuit zone-plane antenna. >

Zone plates with black focal spots.

Abstract: Computer-designed linear and circular zone plates are considered that utilize a π-phase jump in order to create destructive interference in the focus. Intensity distributions in the focal plane as well as along the optical axis are calculated for a few examples. A significant decrease of the black spot diameter in comparison with the dimensions of the ordinary focal spot is obtained. Further reduction is achieved when the central region of the zone plate is obstructed. Some applications to alignment and the schlieren technique are suggested. Experimental results that confirm the calculated distributions are presented.

Astigmatism correction in x-ray scanning photoemission microscope with use of elliptical zone plate

Abstract: We report the impact of an elliptical, high resolution zone plate on the performance of an initially astigmatic soft x‐ray scanning photoemission microscope. A zone plate with carefully calibrated eccentricity has been used to eliminate astigmatism arising from transport optics, and an improvement of about a factor of 3 in spatial resolution was achieved. The resolution is still dominated by the source size and chromatic aberrations rather than by diffraction and coma, and a further gain of about a factor of 2 in resolution is possible. Sub 100 nm photoemission microscopy with primary photoelectrons is now within reach.

Zone plate lens antennas for millimeter and submillimeter wavelengths

Abstract: Zone plate lenses are a type of focusing element which function essentially as differential phase shifters, having a relatively few, coarsely quantized phase delays across the incident beam of radiation. The major advantages are ease of fabrication and much reduced thickness, compared to conventional refractive focusing elements. These considerations are both of particular importance for the submillimeter range, in which manufacturing tolerances for curved optical elements can pose significant problems, and where the absorption of readily available dielectric materials is quite large. In this presentation we briefly review the theory of zone plate lens operations, present a relatively simple method for calculating the aperture efficiency of zone plate lenses used as antennas, and show some theoretical and measured results in the 100 GHz range.

Dual focal point electro-optic lens with a Fresnel-zone plate on a PLZT ceramic.

Abstract: A new dual focal point electro-optic lens that is switchable to focusing and unfocusing is proposed and successfully demonstrated. This electro-optic lens is constructed by coating transparent fine electrodes in the Fresnel-zone plate onto a PLZT ceramic plate. Its focal length changes from 1.25 m to binary at 515 nm with the external voltage of 210 V.

Unified and generalized Fresnel numbers

Abstract: The concept of Fresnel number is discussed and expressions are derived for misaligned optical systems. For the case of perfectly aligned optical elements, the usual number,N, based on a Fresnel zone concept is found to be given byN = (a 2/λ)(D 1/B 1 +A 2/B 2), whereB 1,D 1 andB 2,A 2 are the transfer matrix elements of the optical systems before and after a circular aperture of radiusa respectively. A modified definition of the Fresnel number is proposed for Gaussian beam propagation. This parameterN′ G, is related to the complex beam parameter and may be represented by the angleθ = tan−1 N′ G, found in the familiar Collins chart and its dual representation. A general relation for the transformation of this Fresnel number is found. The expressions for Gaussian beam transformation are thus simplified, since the waist-waist transform is given byN′ G1 =N′ G2 = 0. Finally, these two kinds of Fresnel numbers are written as tensors when applied to cases involving elliptical apertures, astigmatic beams and nonsymmetrical systems.

Focussing optics for a synchrotron-based X-ray microprobe

Abstract: X-ray microprobe experiments at third-generation synchrotron sources will provide trace element analysis of samples with 1 μm × 1 μm spatial resolution and femtogram sensitivity. For these experiments to be possible. X-ray optical elements need to be developed to focus the beam from a hard X-ray undulator to a micron spot size. In June 1991 several different optical elements were tested during a dedicated undulator run at CHESS. The undulator produced radiation similar to that which will be available at third-generation sources like the Advanced Photon Source. Both Fresnel zone plates and multilayer-coated spherical mirrors were tested. With the Fresnel zone plate a spot size of 8.5 μm × 30 μm was achieved in the first order and 6 μm × 20 μm in the second order. With a Kirkpatrick-Baez multilayer mirror system a spot size of 4 μm × 9 μm was achieved. Based on these results, some of the requirements for an optical system suitable for a dedicated microprobe beamline are given.

A Laboratory X-Ray Microscope with a Plasma X-Ray Source

Abstract: A laboratory x-ray microscope has been built with zone plate optics and a pulsed plasma x-ray source. X-ray images of metal patterns, diatoms and 3T3 mouse cells have been taken with sub-optical resolution at a wavelength of about 2.5 nm.

Analysis of lens and zone plate combinations for achromatic focusing of ultrashort laser pulses.

Abstract: Analysis of a combination zone plate and lens system is presented for the design of optical systems to focus ultrashort laser pulses. A system design that is free of propagation-time delay distortion and chromatic aberration is presented.

Method of constructing confocal microscope components

Abstract: A method for constructing a Nipkow disk using a zone plate disk, comprises the steps of constructing a zone plate disk, including the substep of disposing a plurality of focusing means a long a disk, wherein the plurality of focusing means have a common focal distance; placing a photographic plate at the focal distance of the plurality of focusing means; illuminating the plurality of focusing means with a light source such that the illumination is passed through the plurality of focusing means and focused onto the photographic plate thereby creating an image of a plurality of points of focused illumination; and capturing the image created on the photographic plate and using it to construct the Nipkow disk.

Electron beam generated phase zone plates with 30 nm zonewidth for high resolution X-ray microscopy

Abstract: The authors report the manufacture of germanium phase zone plates as objective lenses for high resolution X-ray imaging at 2.4 nm wavelength. The phase shifting properties of the germanium can be used to enhance the diffraction efficiency of a zone plate. Zone plate patterns with structure widths down to 30 nm are generated by low distortion electron beam lithography. The structures are transferred into a 280 nm thick layer of germanium by reactive ion etching (RIE) using a highly selective trilevel mask. 100 nm thick boron doped silicon windows made from single crystal wafers serve as high transmission support membranes. Measurements at the BESSY storage ring proved diffraction efficiencies up to 6.2%. X-ray imaging of a test object showed clearly resolved 30 nm features.

Mirror alignment and/or figure sensing with surface mounted holographic optical elements

Abstract: A procedure for supplying a mirror (22), such as the mirror of an astronomical telescope (60), with holographic optical elements (38), suitable for use with an active mirror alignment system such as a Hartman optical mirror alignment system, is accomplished by constructing each holographic optical element as a separate unitary structure of a transparent substrate (56) with zone plate features. The zone plate features include the channels (64) and ridges (66) of a fragmentary portion of a zone plate etched into a face (58) of the substrate. The substrate is mounted to the mirror by placing the etched face of the holographic optical element in contact with the reflecting surface (68) of the mirror. An adhesive (70) may be applied around the perimeter of the substrate to secure the substrate in its position upon the mirror. This arrangement of mounting the substrate to the mirror protects the etched face of the holographic optical element from environmental damage, and from the stripping and reapplying of a coating during a refurbishing of the mirror.

A review of Fresnel zone plate moire patterns obtained by translations

Abstract: We present equations describing the basic grids that when superposed with themselves and then mutually translated create moire patterns in the form of spherical, equilateral hyperbolic, and linear zone plates. The family of basic grids described forms a complete set of solutions. Moire zone plates can serve as imaging elements with very long, variable focal lengths and have an application in alignment in the three-point technique. The derived solutions are then checked for cases of undesired residual translations and rotations. Evaluations of the focus based on paraxial ray tracing equations are also performed.

Experimental Characterization of Zone Plates for High Resolution X-Ray Microscopy

Abstract: Micro zone plates with outermost zone widths of 40 nm, 35 nm and 30 nm have been used and characterized in the Gottingen x-ray microscope at BESSY These were made through a collaboration between the IBM TJ Watson Research Center and the Lawrence Berkeley Laboratory by electron beam writing Condenser zone plates were made at the Forschungseinrichtung Rontgenphysik using a holographic method

On the sidelobe performance of Fresnel zone plate antennas

Abstract: The Kirchhoff scalar diffraction integral and the image method are used to investigate the close-in sidelobe performance of the simple and phase reversal circular zone plate antennas. It is found that, with fixed aperture dimension, the sidelobe level of a zone plate antenna depends mainly on N, the number of full wave zones composing the plate. When the aperture field taper is kept constant, the sidelobe level of the zone plate decreases significantly when N increases. This means that, with a given zone plate diameter, a small F/D is favorable for obtaining low close-in sidelobes. For a simple zone plate antenna, adequately lowering the edge illumination intensity does reduce the sidelobe level of a centrally opaque version, but it may raise the sidelobes of a centrally transparent one. For the phase reversal zone plate antenna, it is observed that versions with a central disk and a central aperture yield very similar radiation patterns with sidelobes lower than those of the corresponding simple zone plates. Adequately decreasing the edge illumination level produces lower close-in sidelobes. >

Mössbauer-Fresnel zone plate

Abstract: We present a novel application of the Fresnel zone plate geometry in which the Mossbauer effect is used to focus nuclear‐resonant x‐ray photons and thereby to monochromatize synchrotron radiation. The calculated efficiency and energy bandpass of the Mossbauer–Fresnel zone plate monochromator compare well with those of other Mossbauer‐effect monochromators currently in use. The unique capability of focusing Mossbauer radiation into a small (few μm) spot may have applications in spatially resolved and high‐pressure Mossbauer‐effect studies.

Germanium Phase Zone Plates with High Aspect Ratios for X-Ray Microscopy Experiments

Abstract: Phase zone plates with high efficiencies are required in x-ray microscopy to meet the demands of imaging specimens with a low radiation dose and a high contrast. Since the size of the resolution element is equal to the width of the outermost zone and the phase shift is a function of the thickness of the used zone plate material, the fabrication of phase zone plates can lead to high aspect ratios, i.e. to high ratios of the height to the width of the zone.

Design parameters for zone plate antennas

Abstract: The design parameters of the circular Fresnel zone plate are the diameter, focal length, frequency, degree of phase correction, and dielectric material. An experimental design was carried out at 35 GHz for both a transmitting and a reflecting zone plate. It is shown that the rings on the lower half of the zone plate are almost circular, while the rings on the upper half of the zone plate are slightly elliptical with an eccentricity of about 1.20. As beta increases, the eccentricity decreases. The resulting zone plate, therefore, is not much different from a zone plate with an on-axis feed and circular rings. This explains the relatively good performance of such a zone plate when its feed is moved off-axis by as much as 20 degrees . If beta is larger than 20 degrees , then the elliptical design procedure should be implemented to obtain maximum intensity at the focal point. >

Making Soft X-Ray Microscopy Harder: Considerations for Sub-0.1 µm Resolution Imaging at ~ 4 Å Wavelengths

Abstract: Calculations of phase contrast in x-ray microscopy suggest that biological specimens in thick (tens of µm) water layers might be imaged at ~ 4 A wavelength with radiation doses similar to those required for absorption contrast imaging in the “water window” with thinner water layers. This should be possible even with current technology for zone plate fabrication and undulator sources.