Topic
Fresnel zone
About: Fresnel zone is a research topic. Over the lifetime, 2337 publications have been published within this topic receiving 37650 citations.
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20 May 1968
TL;DR: In this paper, a technique for holographically constructing a lens made of stacked Fresnel zone plates on a thick emulsion photographic film which is capable of imaging a wide object field by joining the individual fields of each superimposed zone plate to form an unaberrated composite image is presented.
Abstract: A technique for holographically constructing a lens made of stacked Fresnel zone plates on a thick emulsion photographic film which is capable of imaging a wide object field by joining the individual fields of each superimposed Fresnel zone plate to form an unaberrated composite image. The extent of the individual zone plate field is determined by the emulsion thickness and optical construction geometry and thereby allows restriction of this field to a size capable of unaberrated imaging.
27 citations
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TL;DR: In this article, the geometrical interpretation of Gaussian-beam deformations under reflection at a linear dielectric interface is revised, and an independent nonspecular effect termed the complex amplitude modification exists and that all these effects are necessary for a complete description of the deformed beam.
Abstract: The geometrical interpretation of Gaussian-beam deformations under reflection at a linear dielectric interface is revised. It is proved that, besides the four known geometrical effects, namely, the lateral, focal, and angular shifts and the beam-waist modification, an independent nonspecular effect termed the complex amplitude modification exists and that all these effects are necessary for a complete description of the deformed beam. The new effect is described as a product of reflectance and propagation nonspecular modifications. The amplitude-based and intensity-based definitions of the modified reflection coefficient are given, and substantial differences between them and the Fresnel reflectance are shown. The significance of the propagation modification in the evaluation of the modified reflectance is also explained. Analytical expressions for all the nonspecular effects and for the interrelations among them are derived, and an accurate numerical procedure for their evaluation is discussed.
27 citations
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TL;DR: A nano-focusing module based on two linear Fresnel zone plates is presented, designed to generate a kinoform phase profile in tilted geometry, thus overcoming the efficiency limitations of binary diffractive structures.
Abstract: A nano-focusing module based on two linear Fresnel zone plates is presented. The zone plates are designed to generate a kinoform phase profile in tilted geometry, thus overcoming the efficiency limitations of binary diffractive structures. Adjustment of the tilt angle enables tuning of the setup for optimal efficiency over a wide range of photon energies, ranging from 5 to 20 keV. Diffraction efficiency of more than 50% was measured for the full module at 8 keV photon energy. A diffraction limited spot size of 100 nm was verified by ptychographic reconstruction for a lens module with a large entrance aperture of 440 μm × 400 μm.
27 citations
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TL;DR: In this article, the authors considered a beamed WPT scheme based on a dynamically reconfigurable source aperture transferring power to receiving devices within the Fresnel (near-zone) region.
Abstract: Wireless power transfer (WPT) has been an active topic of research, with a number of WPT schemes implemented in the near-field (coupling) and far-field (radiation) regimes. Here, we consider a beamed WPT scheme based on a dynamically reconfigurable source aperture transferring power to receiving devices within the Fresnel (near-zone) region. In this context, the dynamic aperture resembles a reconfigurable lens capable of focusing power to a well-defined spot, whose dimension can be related to a point spread function (PSF). Near-zone focusing can be achieved by generating different amplitude or phase profiles over the aperture, which can be realized using traditional architectures, such as phased arrays. Alternatively, metasurface guided-wave apertures can achieve dynamic focusing, with potentially lower cost implementations. We present an initial tradeoff analysis of the near-zone WPT concept, relating key parameters such as spot size, aperture size, wavelength, focal distance, and availability of sources. We find that approximate design formulas derived from the Gaussian optics approximation provide useful estimates of system performance, including transfer efficiency and coverage volume. The accuracy of these formulas is confirmed using numerical calculations.
26 citations
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TL;DR: The fabrication and performance of multilayer Al2O3/Ta2O5 Fresnel zone plates in the hard X-ray range and a discussion of possible future developments considering available materials are reported.
Abstract: Fresnel zone plates (FZPs) recently showed significant improvement by focusing soft X-rays down to ∼10 nm. In contrast to soft X-rays, generally a very high aspect ratio FZP is needed for efficient focusing of hard X-rays. Therefore, FZPs had limited success in the hard X-ray range owing to difficulties of manufacturing high-aspect-ratio zone plates using conventional techniques. Here, employing a method of fabrication based on atomic layer deposition (ALD) and focused ion beam (FIB) milling, FZPs with very high aspect ratios were prepared. Such multilayer FZPs with outermost zone widths of 10 and 35 nm and aspect ratios of up to 243 were tested for their focusing properties at 8 keV and shown to focus hard X-rays efficiently. This success was enabled by the outstanding layer quality thanks to ALD. Via the use of FIB for slicing the multilayer structures, desired aspect ratios could be obtained by precisely controlling the thickness. Experimental diffraction efficiencies of multilayer FZPs fabricated via this combination reached up to 15.58% at 8 keV. In addition, scanning transmission X-ray microscopy experiments at 1.5 keV were carried out using one of the multilayer FZPs and resolved a 60 nm feature size. Finally, the prospective of different material combinations with various outermost zone widths at 8 and 17 keV is discussed in the light of the coupled wave theory and the thin-grating approximation. Al2O3/Ir is outlined as a promising future material candidate for extremely high resolution with a theoretical efficiency of more than 20% for as small an outermost zone width as 10 nm at 17 keV.
26 citations