Showing papers on "Zone plate published in 1993"

Fresnel and refractive lenses for X-rays

Abstract: We present a Gaussian beam analysis of X-ray refractive and Fresnel lenses. The X-ray refractive lens is featured by an intrinsic soft (Gaussian) aperture due to strong absorption of X-rays by materials. We defined a parameter N0, the critical Fresnel number (CFN), to describe this optical property. The values of N0 for all practical materials are below 1000 for photon energies exceeding 30 eV, still lower for high-Z materials. The maximum effective Fresnel number of a lens is determined by its material to be 2N0 and its maximum enhancement of X-ray intensity is limited to (2πN0)2, independent of its shape. We found that the refractive lens is likely to be useful for manipulating nearly diffraction limited beam in the hard X-ray region and its application is severely restricted by available fabrication capabilities today. X-ray Fresnel lenses, both in cylindrical and linear forms, are proposed as superior focusing elements for hard X-rays. Their high efficiency, up to 100% in optimal construction, will enable us to manipulate beams with multiple lenses and obtain higher performance optics. Their design and fabrication are discussed in reference to those of X-ray Fresnel zone plates and micro Fresnel lenses for optoelectronics.

High-efficiency Fresnel acoustic lenses

Abstract: Acoustic Fresnel lenses have emerged in recent years as an alternative to the conventional spherical lenses for focusing sound waves in applications such as acoustic microscopy. Fresnel lenses offer the advantage of near-planar geometry and, therefore, ease of fabrication compared to spherical lenses. The Fresnel acoustic lenses reported so far, however, have the disadvantage of low efficiency; only about 40% of the input signal is directed towards the focus. The design and fabrication of lbinaryr acoustic Fresnel lenses that offer much higher efficiencies are described. These lenses, while being still nearly planar, have multiple phase levels to achieve phase shifts other than 0 and 180 degrees as used in conventional, two phase Fresnel lenses. Acoustic Fresnel lenses were fabricated at frequencies of about 1 MHz and 170 MHz. Measurements of the focusing efficiency and point spread function have been performed to characterize the operation of these lenses. Focusing efficiencies in excess of 80% have been achieved with these lenses. The measurements compare well to theoretical simulations

A binary phase zone plate array for laser beam spatial intensity distribution conversion

Abstract: The phase zone plate combines the simplicity of design and fabrication of the random phase plates with the advantage of near field target placement. The flexibility of design allows the cell structure to be easily modified to produce different focal spot shapes. The components are not specific to a particular near field intensity pattern provided several elements can be encompassed by the beam and therefore may be relevant to other laser applications requiring uniform beams on a target provided high spatial frequencies are not detrimental to the laser absorption process. >

Examples of Fresnel diffraction using Gaussian modes

Abstract: Gaussian beam modes, which are normally associated with laser cavities and quasi-optical propagation, can be used to solve some classic problems in Fresnel diffraction. A particular advantage of the technique is that, for the cases of the uniformly illuminated circular aperture, narrow slit and straight edge, it is possible to derive analytical recursive relationships for the mode amplitude coefficients, which allow for speedy computation of the diffraction patterns.

Design procedure for a Fresnel-zone plate antenna

Abstract: A design procedure for two types of Fresnel-zone plate antennas is presented: viz. antennas with absorbing/transparent zones and phase-correcting zones. Design objectives are the optimization of the gain of the lens of the antenna and the side-lobe envelope of its radiation pattern. The design rules are derived from numerical simulations.

Zone plates for zero axial irradiance.

Abstract: We present a family set of zone plates for achieving zero axial irradiance at their foci. This kind of zone plate may be useful in optical alignment.

Generalized Zone Plates Focusing Light into Arbitrary Line Segments

Abstract: A new computer-generated generalized zone plate is proposed, which is able to concentrate the incident beam into a line segment of various length and arbitrary inclination to the optical axis, as well as unrestricted distribution of the longitudinal intensity. The approach is based on the energy conservation principle and equations of the paraxial ray tracing, both considered in the cartesian coordinate system. Hyberbolic, elliptic, linear, and conical zone plates are shown to be limiting cases of the proposed element. Other specific cases, e.g. a new element focusing into a segment of the optical axis, are also derived.

Fabrication of hard x-ray phase zone plate by x-ray lithography

Abstract: Fresnel phase zone plates for hard x‐ray microfocusing have been fabricated. An original x‐ray mask written by e‐beam lithography was replicated into thick PMMA by x‐ray proximity printing. The pattern was transferred into gold and nickel by electroplating. A smallest linewidth of 0.25 μm with an aspect ratio of 14 in the metal pattern has been achieved. Thickness of fabricated zone plates was dictated by a π‐phase shift requirement for focusing of the x rays at 8 and 20 keV energies.

Fresnel zone plate reflector incorporating rings

Abstract: A novel high-efficiency Fresnel zone plate reflector antenna is presented. The reflector consists of an inhomogeneous array of circular conducting rings printed on a grounded substrate. By adjusting the geometrical parameters of the rings and the distances between them, the reflector provides a space-varying phase correction required for focusing an incoming plane wave. Compared with a phase reversal zone plate, an average of 3-dB gain improvement and significant sidelobe reduction have been obtained. >

Phase correcting zone plate.

Abstract: A zone plate focusing radiation comprises a plurality of surface portions (20a, 20b, 20c, 20d, 30) corresponding to zones of the zone plate. The surface portions are positioned in a plurality P of parallel planes such that each surface portion diffracts radiation out of phase with respect to adjacent surface portions such that radiation diffracted by the surface portion constructively interferes at a focus of the zone plate. The Pth plane is dielectrically spaced from the first plane by nμ, where μ is the wavelength of the radiation and n is an integer.

Dynamical theory of stratified Fresnel linear zone plates

Abstract: A dynamical theory is given for calculating the performances of stratified Fresnel linear zone plates (SFLZP’s). The Born expansion extended to the Fresnel diffraction is used to prove a fundamental theorem giving the diffraction efficiency and the diffraction pattern of transmission or reflection SFLZP’s. The method is valuable as long as the wavelength is smaller than the characteristic parameter of the zone plate. It allows us to evaluate the performances of reflection multilayer SFLZP’s, i.e., the so-called Bragg–Fresnel optics recently developed for x-ray optics.

Pupil conjugation connecting device in projection optical system

Abstract: PURPOSE:To obtain a projection optical system in which a Fresnel fringes of Fresnel-elements having a prism operation and a positive power are not projected by arranging optical elements having a periodic construction by shifting toward an optical axis from an intermediate-image position. CONSTITUTION:A pupil conjugation connecting elements (device) 30 is constituted of eccentric Fresnel lenses 31, 32 divided into two sheets, correction lenses 33, 34 inserted between the Fresnel lenses 31 and 32. The center F1 of the eccentric Fresnel lenses 31 and 32 is made eccentric to the center F2 of correction lenses 33 and 34. When the eccentric Fresnel lenses 31 and 34 are arranged by shifting from an inter-mediate image 13 in this way, Fresnel fringes of eccentric Fresnel lenses 31 and 32 are made to be a defocus state to a projection lens 21 of a second projection lens system 20. Thus, the image of the fringes is never formed inside a projected image.

Multilayer phase correcting fresnel zone plate reflector antennas

Abstract: Owing to its flat nature and light weight etc., the Fresnel zone plate antenna is becoming very attractive for such applications as DBS reception and receive-only VSAT. The disadvantages of low efficiency and high sidelobes of the simple and the phase reversing zone plates can be improved by using phase correcting techniques. In this paper, a systematic investigation on the efficiency and sidelobe performance of subzone phase correcting zone plate antennas is presented. The design of a form of multilayer phase correcting zone plate reflector is described. A quarter-wave zone plate reflector constructed with three dielectric layers and metallized rings is reported, with measured peak efficiency of 55 per cent.

Diffraction of multilayer gratings and zone plates in the x-ray region using the Born approximation

Abstract: New devices combining the Bragg reflection from periodic multilayer structures with Fraunhofer or Fresnel diffraction arising from lateral patterning of the multilayer are now available for x-ray optics. Using the Green’s-function method, we establish an integral equation for the scattered amplitude that is valid in the framework of both Fraunhofer and Fresnel diffraction. The scattered amplitude is given in the first and the second Born approximations for multilayer mirrors, laminar and sawtooth-profile multilayer gratings, and linear multilayer zone plates. The main diffractive properties of these devices are deduced. The efficiencies are computed in the first and/or in the second Born approximation and are compared with efficiencies obtained from a rigorous electromagnetic theory when they are available.

On the subzone phase correction of fresnel zone plate antennas

Abstract: Subzone phase correction is a practical technique to produce high-efficiency Fresnel zone plate antennas. In this article a strict theory underlying the technique is presented. A closed-form expression of the focal field for the subzone phase correcting Fresnel zone plate (FZP) illuminated by a plane wave is given first. The subzone division and the corresponding phase correction are then optimized to produce the maximum focal field intensity. To overcome the difficulty of placing many subzone phase shifters in the narrow outer full-wave zones, an aperiodic subzone phase correction technique is proposed.

Eccentric Fresnel lens sheet and method of making same

Abstract: An eccentric Fresnel lens is formed from a concentric Fresnel lens sheet or Fresnel lens sheet mold. The concentric Fresnel lens sheet or mold is cut to produce an eccentric Fresnel lens having a center offset from the optical axis of the concentric Fresnel lens.

Zone plate x-ray microscope using a laser plasma source

Abstract: An imaging x-ray microscope using an incoherent laser plasma source and zone plates is reported. The He-like line of 4.03 nm (1 X 1014 photons/sr/pulse) from a carbon plasma produced by a compact glass laser is used as a source. The x-ray source is monochromatized by a condenser zone plate and a pinhole. As an x-ray image detector, a Kodak 101-07 film and an MCP or a cooled backside illuminated CCD are used. An image of the #1000 copper mesh is obtained by a single x-ray pulse at a magnification of 10 by the CCD. In the case of a singe pulse, the magnification is limited so that enough photons are incident on a pixel of the CCD. Thus, the spatial resolution is limited. Further improvement such as an ellipsoidal mirror with multilayer coating is considered to improve the resolution.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Programmble diffractive optics with a ferroelectric liquid crystal SLM in a binary phase-only mode

Abstract: We report on the performance and application of a commercially available 128 X 128 pixel, electrically addressed ferroelectric liquid crystal spatial light modulator (FLCSLM). In combination with appropriate polarization optics the FLCSLM can be configured as a 2-level phase only modulator. The performance of this `programmable phase transformer' (PPT) is demonstrated by using it in conjunction with a positive lens to produce near diffraction limited, reconfigurable, arrays of spots in the Fourier plane of the lens. Near diffraction limited performance is also shown for the PPT with pixels configured to act as a Fresnel zone plate. Finally, the pixel configuration for spot array generation is combined with that for zone plate to produce spot arrays without the aid of a lens. Improved performance with 2-dimensional over 1-dimensional optimization procedures is also demonstrated.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Image enhancement through deconvolution

Abstract: Several groups have been developing x-ray microscopes for studies of biological and materials specimens at suboptical resolution. The X1A scanning transmission x-ray microscope at Brookhaven National Laboratory has achieved 55 nm Rayleigh resolution, and is limited by the 45 nm finest zone width of the zone plate used to focus the x rays. In principle, features as small as half the outermost zone width, or 23 nm, can be observed in the microscope, though with reduced contrast in the image. One approach to recover the object from the image is to deconvolve the image with the point spread function (PSF) of the optic system. Toward this end, the magnitude of the Fourier transform of the PSF, the modulation transfer function, has been experimentally determined and agrees reasonably well with the calculations using the known parameters of the microscope. To minimize artifacts in the deconvolved images, large signal to noise ratios are required in the original image, and high frequency filters can be used to reduce the noise at the expense of resolution. In this way we are able to recover the original contrast of high resolution features in our images.

Performance comparison of hard x-ray plates fabricated by two different methods

Abstract: Two types of fabrication methods have been developed to fabricate Fresnel zone plates for focusing x-rays in the 5 - 25 keV energy region. These two fabrication methods are discussed in terms of spatial resolution and focusing efficiency, which are two important parameters that characterize the performance of a Fresnel zone plate. Experimental characterization of the zone plates fabricated by the two methods are described and the results are discussed.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Stigmatic imaging by zone plates: a generalized treatment

Abstract: We present a new and succinct formulation for the zone radii of zone plates in terms of the focal length and the object-to-image throw of the imaging configuration. This treatment enables us to develop a method for dimensionless analysis of zone-plate parameters for stigmatic imaging of axial-object points. A set of graphs depicts the essential design parameters of zone plates over a wide range of the electromagnetic spectrum, from the infrared to x-ray wavelengths. These nomographs are useful in designing zone plates for given applications, particularly in rapid assessment of the feasibility of zone plates for specified requirements in the early stages of design.

Illumination optical system

Abstract: PURPOSE:To eliminate the optical damage of an optical element by a method wherein a homogenizer which makes the brightness distribution of an illumination light flux uniform and a condensing optical system with which an object to be irradiated is irradiated are constituted of a zone plate. CONSTITUTION:A light flux 2 which is radiated form a laser light-source generation device 1 is reflected by a reflector 3; it is incident on a homogenizer 4 as an optical element which forms the more uniform brightness distribution of a plane to be irradiated. The light flux which is divided by the homogenizer 4 forms a secondary light source 5 on the focal plane of the homogenizer, and illuminates, by using an installed condensing lens 6, a plane 7 to be irradiated where a mask is installed. The homogenizer 4 and the condensing lens 6 are formed of a zone plate. Thereby, it is possible to constitute an illumination optical system wherein the loss of the quantity of light is small with reference to a short-wavelength light source and the optical damage of an optical component is not caused.

The self-focusing Fresnel-Dammann grating and the Fresnel binary CGH for compact 2-D light spot array generation

Abstract: The authors have described the design and demonstrated the performance of two types of lensless array generator. The Self-focusing Fresnel-Dammann grating (SFD), and the Fresnel hologram. The SFD is based on a conventional Dammann grating, but obviates the need for extraneous Fourier transform lenses, by combining the grating with a Fresnel zone plate, in an exclusive-OR fashion. No alignment is required and no bulky or dispersive refractive elements are used. The Fresnel hologram can be designed for high fanout, but the design must take into account the phases of the light spots in the image array. The authors have demonstrated this for an 8times8 fanout element, where a set of random phases in the output gave rise to a satisfactory performance, whilst another set of phases gave an undesired, although interesting, result. The authors have also demonstrated a 30deg slanted axis, random phase design, generating a two dimensional array of 8times8 beams, used in reflection, and operating in a multiple reflection, planar-optic configuration

Varifocal fresnel zone plate

Abstract: The invention relates to a varifocal (variable focus) Fresnel-zone plate which includes a succession of absorbent concentric rings and of transparent concentric rings enabling incident light of wavelength lambda to be focused. This Fresnel-zone plate possesses means enabling the absorbence and the transparency of the concentric rings to be varied so as to reconfigure the said plate and thus to change the focus. Depending on the spectral domains, this can be a Fresnel-zone plate using electrochromic materials, dispersed liquid-crystal polymers or even electrolytic depositions based on silver allowing X-ray focusing.

Blazed Fresnel zone lenses approximated by discrete step profiles: effects of fabrication errors

Abstract: Blazed Fresnel zone lenses for 1.5 j.m wavelength were fabricated in quartz glass by means of microstructuringtechnology. The blazed profile in each zone of the lenses was approximated by 2, 4, and 8 discrete levels. The effects offabrication 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.1. INTRODUCTIONDiffractive optical lenses are beginning to play an important role in a variety of applications'. This is especially true for those lenses that can be fabricated with microstructuring techniques that are adapted from microelectronic technology. The most common of these diffractive lenses are Fresnel zone lenses that are recorded as surface reliefgratings. In order to obtain the maximum diffraction efficiency, the shape of the grating profiles must be blazed.Unfortunately, such blazed profiles are difficult to fabricate, so they must be approximated by a staircase-like profilehaving a number of discrete levels.Multilevel zone plate lenses can reach high efficiencies depending on the number of discrete levels that are used. Thefabrication of these elements involves multiple steps of repeated pattern transfer and either anisotropic etching orthin film deposition3 to build up the desired surface profile. During these steps a variety of fabrication errors can beintroduced that degrade the optical quality and reduce the diffraction efficiency significantly. Some of these errors andtheir effects have been considered in applications with visible and far infra-red radiations2'.

X-ray microscopy studies with the Goettingen x-ray microscopes

Abstract: Zone plates with improved resolution have been constructed by electron beam lithography. With these zone plates features as small as 30 nm can be imaged without astigmatism. By using the phase shifting property of the zone plate material and by an improved etching technique, groove efficiency values up to 10% have been measured. A new type of foils for the support of the zone plates as well as for the x-ray windows are more stable under synchrotron radiation than the polyimide foils used before and have a higher transmission for x-rays in the `water-window' region. The x-ray microscope installed at BESSY, Berlin, Germany was modified in such a way that the environmental chamber is now placed in air with better access to the specimens under investigation. In addition, a light microscope was incorporated in the x-ray microscope providing a better practicability to adjust object details to the object field of the x-ray microscope, selecting another object or object detail to be investigated, and prefocussing the object for x-ray imaging. With the improved x-ray microscope different wet biological specimens and test structures were investigated, showing features as small as 30 nm. The x-ray microscope using a pulsed plasma x-ray source, installed in Gottingen, Germany was modified in such a way that instead of a zone plate an ellipsoidal mirror is used as the condenser. The pulsed plasma x-ray source was improved too, i.e., the number of pulses needed for an image is reduced.

Linear-Fresnel-Zone-Plate-Based Two-State Alignment Method for Sub-0.25 µm X-Ray Lithography System

Abstract: In this paper, we present a linear-fresnel-zone-plate-based two-state alignment method developed at the Center for X-ray Lithography. The alignment system uses a linear Fresnel zone plate (LFZP) as a mask alignment mark and an array of dots as a wafer alignment mark. The alignment error signal extraction is based on a two-state modulation of the incident light. The optical system is arranged outside of the exposure X-ray path and alignment can be performed during X-ray exposures. In the experiment, we obtained an alignment signal depth of focus larger than 4 µm and the gap change between the mask and wafer did not affect the alignment position. The X-ray double-exposure experiment on the system demonstrated an alignment accuracy better than 0.035 µm (3σ) on both Al and silicon nitride marks.