Showing papers on "Zone plate published in 1994"

Three-dimensional micro-Fresnel optical elements fabricated by micromachining technique

Abstract: We report, for the first time, a three-dimensional binary phase micro-Fresnel optical element standing perpendicular to the substrate. The lens is fabricated by micromachining technique. The lens has a diameter of 650 µm, a focal length of 0.5 mm, and an optical axis of 1 mm above the surface of the substrate. Light from an optical fibre is successfully collimated by the micro-optical element, and the beam profile closely approximates a Gaussian shape.

Binary-phase zone plate arrays for the generation of uniform focal profiles

Abstract: The generation of uniform focal intensity profiles is important for a number of applications, including laser–plasma interaction experiments. We report on a focusing system that uses a novel binary-phase optic capable of producing efficient two-dimensional uniform top-hat intensity optical and x-ray profiles.

High-performance multilevel blazed x-ray microscopy Fresnel zone plates: Fabricated using x-ray lithography

Abstract: Diffractive lenses are becoming the optical elements of choice for many applications. One type of diffractive lens, the binary zone plate, has already demonstrated high‐resolution performance experimentally. However, in order to increase the diffraction efficiency of these zone plates, a blazed grating profile must be used. This can best be approximated by a staircase grating profile, created by multilevel exposures. Using x‐ray lithograph, we fabricated for the first time circular, linear bi‐ and trilevel zone plates, with gold structures 0.75 μm thick (per level), on silicon nitride substrates. The zone plates were designed for use at a wavelength of 1.54 A, and had a theoretical efficiency of 68.5% for bilevel and 81.5% for trilevel zone plates. Due to the large depth of focus and high resolution inherent to x‐ray lithography, the finished zone plate exhibits very steep sidewall profiles, with linewidth resolution down to 0.25 μm. Such vertical sidewalls are essential for achieving high lens efficiency. Fabrication errors, such as thickness variation in the electroplated gold and misalignment, were considered, and their effect on the optical efficiency of the zone plate was estimated. Alignment errors between levels were minimized, achieving a best result of 25 nm (3σ). In fabricating the zone plates, we employed standard integrated device tools, such as a Leica Cambridge Electron Beam microfabricator (EBMF) 10cs/120 electron‐beam writer for the x‐ray mask fabrication, and a Suss 200 x‐ray stepper for the multilevel exposures. Thus, we have shown that it will be possible to fabricate many lenses, with a variety of optical characteristics, in one wafer.

Scanned optical fiber confocal microscope

Abstract: The size and weight of conventional optical microscopes often makes them inconvenient for use on the human body or for in-situ examination during materials processing. We describe a new fiber-optic scanning confocal optical microscope which could have a total outside diameter as small as 1 mm, and should lend itself to applications in endoscopy or to optical in vivo histology. The first experimental device utilizes a single-mode optical fiber for illumination and detection. The scanning element is a mechanically resonant fused silica cantilever 1.5 cm long and 0.8 mm across, with a micromachined two-phase zone plate objective mounted at one end. The cantilever is electrostatically scanned near resonance in two dimensions, generating a Lissajous pattern which is scan converted to conventional video for real time display or digitization. The objective lens has N.A. equals 0.25 at (lambda) equals 0.6328 micrometers , with a measured spot size of 1.8 micrometers FWHM.

Phase-contrast X-ray microscope

Abstract: An X-ray microscope has the following features: a pulsed x-ray source that delivers an intense line radiation, an annular condenser that focuses the radiation of the X-ray source on the object to be investigated, an X-ray optics constructed as a micro zone plate that images the object with high resolution on an X-ray detector, and a phase ring positioned in the rear focal plane of the micro zone plate and applies to the zero order X-ray radiation coming from the object a phase shift, with respect to the higher order radiation deflected by the object structures, which is determined by the thickness and material of the phase ring. The phase shift amounts, for example, to 90° or 270°.

Analysis of a phase-correcting Fresnel-zone plate antenna with dielectric/transparent zones

Abstract: The dielectric zones of phase-correcting Fresnel-zone plate antennas are usually considered to be ideal phase-shifters. In this paper, we model the interaction between an incident electromagnetic wave and the dielectric material of such an antenna more accurately and present a new calculation method to obtain its far-field radiation pattern. A comparison between the patterns calculated following the new and the old approach demonstrates the necessity of using the new one.

Apparatus and process for using fresnel zone plate array for processing materials

Abstract: An apparatus and a process of using a Fresnel zone plate array (55) is utilized for processing materials. The Fresnel zone plate array (55) has a plurality of discrete subapertures (A - X) with each subaperture containing image information at a discrete working distance from the plate; each image produced by a subaperture (A - X) of the Fresnel zone plate array (55) typically differs from adjacent images from adjacent subapertures typically in size, shape or gain. A beam is scanned and registered to a discrete selected subaperture on the plate to cause an image from the subaperture to form on a work piece (53') located at the working distance of a scanned subaperture. At each location for processing utilizing a particular selected image, the work piece (53') is positioned, and the laser pulsed with the selected image causing processing of the work piece (53').

Focusing performance of epoxy‐ and air‐backed polyvinylidene fluoride Fresnel zone plates

Abstract: In this paper the focusing performance of epoxy‐ and air‐backed polyvinylidene fluoride (PVDF) Fresnel zone plate (FZP) transducers are investigated. This work is motivated by an interest in constructing integrated, polymer FZP transducers for imaging applications on a silicon substrate using integrated circuit fabrication techniques. While it is well known that using an impedance matched backing facilitates broadband transducer performance, to the authors’ knowledge the effects on the acoustic beam patterns of polymer FZPs have not been reported. A model for the ideal zone plate is also presented, and a general pressure transfer function is derived in order to generate theoretical beam profiles. Epoxy‐ and air‐backed, three‐zone FZPs were constructed using 111 μm thick PVDF. The devices were tested in an ultrasound scanning tank while operating at 5 MHz. The focal plane profile for the epoxy‐backed device was in good agreement with that predicted for the ideal zone plate. In addition, the epoxy backing was found to dampen higher order radial mode excitation. The radial modes are believed to be responsible for the narrow main lobe and elevated side lobes found in the focal plane profile for the air‐backed device.

Zone-Plate X-Ray Microscope Using a Laser Plasma Source

Abstract: An imaging X-ray microscope using a laser plasma X-ray source, an objective zone plate and an ellipsoidal condenser mirror with multilayer coating is described. The 3.37 nm line emission from a carbon plasma is filtered and focused by the ellipsoidal condenser mirror and used as a light source. A magnified image (magnification: ×287) of a gold zone plate was obtained by a back-illuminated charge coupled device (CCD) whose pixel size is 22 µm×22 µm. The 0.4-µm-period pattern (outermost zones: 0.27 µm line and 0.13 µm space) is clearly resolved.

Effect of fabrication errors on multilevel Fresnel zone lenses

Abstract: Blazed Fresnel zone lenses for the 1.5-μm wavelength were fabricated in quartz glass by means of microstructuring technology. The blazed profile in each zone of the lenses was approximated by two, four, and eight discrete levels. The effects of fabrication errors, such as depth and alignment errors, on the diffraction efficiency of the different Fresnel zone lenses were investigated. Further the location and intensity of the parasitic foci appearing due to the discrete level approximation are calculated. Theoretical results along with experimental measurements are presented.

Sub-micron spatial resolution of a micro-XAFS electrostatic microscope with bending magnet radiation: Performance assessments and prospects for aberration correction

Abstract: The X-ray photoemission electron microscope (XPEEM) has been shown to be a valuable tool for small-area X-ray absorption fine-structure (XAFS) spectroscopy, and for state-selected imaging. The instrument currently in regular operation on bending-magnet monochromators uses electrostatic optics to create an image of a sample surface in vacuum. The instrument can be operated on a wide variety of X-ray and VUV beamlines, and the spectral resolution is determined by the beamline monochromator. The spatial resolution is determined primarily by the aberrations of the immersion lens accelerating field and the objective lens, although other factors such as surface roughness play an important, though less fundamental role. We have tested the spatial resolution of micro-XAFS with a high quality test object, consisting of a free-standing circular zone plate made of gold. These tests confirm the assessment that chromatic aberration limits the performance of the optics, because of the wide range of kinetic energies of secondary electrons produced in XAFS spectroscopy, and the highly asymmetric intensity distribution of these secondaries. One attempt at solving the chromatic aberration problem is the use of an energy filter, which solves the problem by allowing only a narrow band of electrons to produce an image. We describe an alternative approach, based on chromatic aberration correction, which has great potential for an XPEEM instrument with extremely high transmission, and spatial resolution below 10 nm. We also point out the performance improvements to be expected when XPEEM is adapted to high-throughput undulator beamlines.

Analytical theory of zone plate efficiency.

Abstract: The theory is developed which enables us to derive explicit formulas for the efficiency of thick zone plates. The theory employs the method of coupled wave equations. The solutions obtained can be applied to the large class of zone plates and diffraction structures which are locally equivalent to sliced multilayers. Based on this theory we find limits to the diffraction efficiency of zone plates due to refraction and absorption of indexes of materials. The results can be applied in x-ray, neutron, and atom optics.

Diffraction efficiency of low-resolution Fresnel encoded lenses.

Abstract: A mathematical model to describe the behavior of low-resolution Fresnel lenses encoded in any low-resolution device (e.g., a spatial light modulator) is developed. From this model the diffraction efficiency is calculated in terms of all the parameters that characterize these lenses.

High-efficiency cosine-approximated binary Gabor zone plate

Abstract: A cosine-approximated binary Gabor zone plate is proposed. The zone plate is fabricated by standard photographic techniques. It was evaluated by simulation and by experiment to match the focusing behavior of an ideal Gabor zone plate, but it has a focusing efficiency at least 23% higher than that of a binary Gabor zone plate. Duplication of an alphabetic character to form a 4 × 4 array of images with little astigmatism by the proposed zone-plate array is demonstrated.

Multilayer offset Fresnel zone plate reflector

Abstract: An offset phase-correcting Fresnel zone plate (FZP) reflector antenna based on the multilayer configuration is presented. The reflector consists of a conducting ground and four layers of conducting patterns separated by four dielectric substrates. An experimental prototype designed at 10.39 GHz was fabricated and tested. With a 0.32 m by 0.34 m elliptical reflector aperture and a pyramidal feedhorn, the antenna achieved -20-dB sidelobe level and 61% maximum efficiency. Compared with a phase reversal FZP of the same size, a 3.3-dB gain improvement and significant sidelobe reduction were obtained. >

Millimeter-wave Fresnel zone plate antennas

Abstract: Fresnel zone plate antennas have seen extensive research in recent years. Both transmission and reflection types have been analyzed and tested, and found to give excellent performance. Parameters such as far-field patterns, gain, efficiency, frequency dependence, aberrations, scan capability, focal region properties, and off-axis performance have been examined. While most zone plates are planar, curved (spherical or paraboloidal) versions have been found to offer certain advantages, such as sharpness of focus or larger field of view. In general, millimeter-wave results are emphasized.

Imaging by zone plates: axial stigmatism at a particular order

Abstract: A Fresnel zone plate (FZP) produces simultaneously multiple images, both real and virtual. In general, none of the images is stigmatic beyond the paraxial domain. Axially stigmatic imaging by FZP’s calls for unique values of zone radii corresponding to each combination of the order number of the image and the object distance. In a recent paper [ J. Opt. Soc. Am. A10, 69 ( 1993)] we presented a set of nomographs for ready estimation of zone-plate parameters. The treatment dealt with the special case of a positive first-order image produced by a FZP. We now extend the study to incorporate imaging of any specific order. It is shown that, with a simple redefinition of the variables, the nomographs presented in the earlier paper retain their practical usefulness.

Offset Fresnel zone plate antennas

Abstract: The theory of offset Fresnel zone plate antennas is presented. Explicit formulae for the design of the zone boundaries for the offset Fresnel zone plate are given. Theorectical equations and numerical results for the far-field analysis are presented. It is found that when the offset angle increases, the zone boundaries become more elliptic and the plate becomes more asymmetric in the E-plane. With the number of full wave zones and the plate width in the W-plane fixed, the plate width in the E-plane increases with the offset angle, which keeps the projected aperture area constant. Within a limited range of offset angles, the offset configuration can be employed without degrading the radiation performance much. For large offset angles, however, the asymmetry of the configuration may lead to increased sidelobes and decreased antenna directivity. An experiment with one particular phase reversal zone plate antenna with 30° offset angle shows good agreement between the measured antenna pattern and the theoretical prediction.

Stepped lens with Fresnel surface structure produced by lithography and process for manufacturing of same

Abstract: In a stepped lens with a Fresnel surface structure produced by lithography and a process for fabricating same, the high potential exposure speed of high-speed electron-beam exposure systems which work with variable rectangular beam cross sections is converted in such a way that stepped Fresnel type lenses can be fabricated with high efficiency and, in so doing, the required amounts of data is reduced. According to the invention, radiation dose distributions which correspond to cylindrical lenses are exposed one upon the other, at least one of the radiation dose distributions corresponding to a Fresnel type cylindrical lens. Lens structures with any desired lens curvature, from radially spherical to elliptical, can be efficiently produced by lithography by the disclosed process.

Subnanometer alignment system for x‐ray lithography

Abstract: Proximity printing with soft x rays is a leading contender for very large scale integrated circuit lithography below 0.25 μm. It will require overlay accuracy far below the 100 nm (3σ) typical of today’s systems. In addition, it should use wafer marks which permit planar resist flow, so their apparent position is not distorted. We report an alignment system which uses a linear zone plate on the mask to focus laser light into a line on the wafer. The wafer mark is the boundary between two adjacent fine pitch gratings. These gratings diffract the light into photodiodes. The gratings either differ slightly in pitch or by 180° in phase. This configuration minimizes the disturbance to the resist as it flows over the alignment mark. In the case of gratings with slightly different pitch the light from each grating is detected by one‐half of a split photodiode. This arrangement has good sensitivity and a very wide capture range. The phase shift gratings have reduced capture range but enhanced sensitivity because ...

Subharmonic focal-length intensities formed by Fresnel lenses

Abstract: Binary Fresnel lenses produce focused spots at subharmonics of the principal focal length of the lens. The intensities of these focal spots can be controlled by variation of the relative widths of the rings of the Fresnel lens compared with the spacings between the rings. Theory is presented and experimental verification is provided with Fresnel lenses written onto the magneto-optic spatial light modulator.

Optical displacement sensor employing reflected light of four wavelengths to determine displacement and the refractive index of the medium

Abstract: An optical displacement sensor suitable for use in drowned environments where the refractive index of a medium in the optical path may vary, comprises a light source emitting first to fourth wavelengths. The first and second wavelengths are within the infrared region of the spectrum, whereas the third and fourth wavelengths are in the visible region of the spectrum. A zone plate focuses the first and second wavelengths to respective positions substantially at the extremes of movement of a reflective element whose position is to be measured. The zone plate also focuses the third and fourth wavelengths to respective positions. A cold mirror is interposed between the zone plate and the reflective element and is arranged to transmit the first and second wavelengths and to reflect the third and fourth wavelengths. The ratio of the intensities of the light reflected from the cold mirror gives information about the refractive index of the medium in the optical path. This information can be used to correct the measurement of the position of the reflective element which is determined by the ratio of reflected intensities of the first and second wavelengths.

A scanned source X-ray microscope

Abstract: The first results using a scanning X-ray microscope, with zone plate optics, specifically designed for use with a laser-plasma X-ray source are reported. Unlike previous microscopes of this type, in which the specimens were mechanically scanned, in the present arrangement the specimen was kept stationary and the source was moved, the zone plate demagnifying this movement on the specimen. Images of test specimens show an edge resolution of 0.35+or-0.14 mu m, apparently limited by noise.

On the radiation characteristics of Fresnel zone plate antenna

Abstract: This paper presents some numerical results of radiation patterns of the Fresnel zone plate antenna (FZPA) based on the vectoral Kirchhoff diffraction integral. The results of beamwidth, sidelobe level and efficiency vs zone type, focal length and feeder illumination are given as design criteria. The experimental data for a FZPA fed by a E-sectoral horn are provided for verifying the availability of the theoretical analysis.

Liquid crystal lens

Abstract: PURPOSE:To obtain the liquid crystal lens which utilizes a liquid crystal cell formed by arranging flat plate type substrates opposite each other and provides it with a lens function. CONSTITUTION:Transparent conductive films 11 and 21 and orienting films 12 and 22 are formed on the respective internal surfaces of a couple of flat plate glass substrates 1 and 2 arranged opposite each other, and liquid crystal 3 is charged in the space partitioned between both the substrates 1 and 2 to form the liquid crystal cell, and a couple of polarizing plates 5 and 6 are arranged outside the liquid crystal cell on both sides. Then the transparent conductive film 21 of one substrate 2 is arranged in plural concentric zones and when a voltage is applied, an even-numbered Fresnel zone part becomes dark. Thus, the lens function of a Fresnel zone plate is obtained at the time of the voltage application.

Lighting optical system

Abstract: PURPOSE:To obtain a lighting optical system effectively applicable to object lens with large numerical aperture corresponding to a light source with strong directivity without bending the light axis of the optical system. CONSTITUTION:In a lighting optical system of a focusing optical system, a secondary light source is formed with a zone plate. The light from this secondary light source is cast on a sample through a slanting incidence mirror 3 having a curved surface of revolution formed by revolving a non-spherical surface. For example, a small-diameter beam 1 from a light source with strong directivity is transmitted in the zone plate 2 and the light beam is converged with the zone plate 2 and then transmitted to a slanting incidence mirror 3 formed with an ellipsoidal or revolution. By placing a light shield plate 6 having a pin hole through which the light beam is penetratable, at the convergence point in this case, the incidence light can be separated into spectrum.

A Low Cost W-Band Doppler Radar

Abstract: In order to measure accurately the instantaneous real speed on the sea, a low cost Doppler radar has been developed in the W-band. The main parts of the device are a Gunn diode oscillator and a Schottky diode mixer integrated on the same printed circuit, on either side of the emission and reception system including a conical horn with a Fresnel zone plate, excited by the dipole antennas of emission and reception. The Doppler signal, which is obtained after mixing, must be in the order of tens of kHz.

Multilayer reflection-type zone plates and blazed gratings for the normal incidence soft x-ray region

Abstract: Here we report on the fabrication and analysis of two different types of laterally structured multilayers, which act as highly efficient x-ray optical elements for focusing or spectral dispersion of soft x-rays at (near) normal incidence. The microfocusing of soft x-rays at (near) normal incidence with plane reflection optics can be obtained by multilayer Bragg-Fresnel zone plates. A circular condensor zone plate structure (2.9 mm diameter, 417 zones, inner zone radius 50 micrometers , outer zone width 0.9 micrometers ) has been recorded by holographic lithography followed by ion beam etching into a Mo-Si multilayer mirror of 24 periods and a doublelayer thickness of 7.2 nm. The focusing properties analyzed by soft x-ray reflectometry at (lambda) equals 13.8 nm show a focal spot size smaller than 40 micrometers measured 160 mm behind the multilayer zone plate. Multilayer blazed gratings offer the opportunity for highly resolved spectral dispersion of soft x-rays due to the possible combination of high efficiency and high diffraction orders with almost the whole intensity diffracted in one diffraction order. The sawtooth profile of a blazed grating structure (1221 l/mm, blaze angle 1.5 degree(s)) has been ruled into a 200 nm thick Au-film which has been deposited onto a plane glass substrate. A Mo/Si multilayer of 15 periods and a doublelayer thickness of 7.2 nm has been deposited onto the grating substrate. In order to smooth the rough Au-surface and to prevent interdiffusion of the Au-film with the upper Mo-Si multilayer a carbon film has been evaporated onto the Au-grating surface before the deposition of the soft x-ray coating. This procedure results in a significant increase of diffraction efficiency. The multilayer grating has been matched working on blaze in the third diffraction order, where an absolute diffraction efficiency of 3.4% at (lambda) equals 14 nm has been measured, while only 1.1% has been achieved for a similar grating without a carbon interlayer.

Applications of the Xia Scanning Photoemission Spectromicroscope for Element Identification on Material Surfaces

Abstract: The Second Generation Scanning Photoemission Microscope at the beamline X1a of the National Synchrotron Light Source (NSLS), X1A SPEM II, is designed for spatially resolved elemental and chemical analysis by X-ray Photoelectron Spectroscopy (XPS) on material surfaces. Based on Fresnel Zone Plate (ZP) microfocusing techniques with the use of a bright and coherent photon source, this microscope is capable of acquiring XPS spectra from a small area irradiated by the focused beam and taking element-specific (using photopeaks) or chemical-state-specific (by detecting the chemical core level shifts) images with a spatial resolution defined by the focused spot size.