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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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TL;DR: In this paper, the location and magnitude of the axial pressure amplitude extreme were investigated using Fresnel zones for a model of a disc transducer vibrating in a plate mode with a single node.
Abstract: The mechanisms which underline the location and magnitude of the axial pressure amplitude extreme have been investigated using Fresnel zones for a model of a disc transducer vibrating in a plate mode with a single node. It was found that the position of the last axial minimum gives an effective radius equal to the radius of the node. The magnitude of excitation of the anti-phased outer ring can be obtained from the ratio of the amplitude of the last axial minimum and last axial maximum
1 citations
16 Nov 2000
TL;DR: In this article, a tri-layer process was used to produce nickel zone plates with the outermost zone widths of 40 nm, 30 nm and 25 nm with the tri-level process yielding 21.6, 18.0% and 14.7% first-order groove efficiency, respectively.
Abstract: Soft X-ray microscopes require high-spatial-resolution Fresnel zone plates with high and uniform diffraction efficiency as imaging optics. The combination of the zone height for optimal diffraction efficiency with the fact that the first-order spatial resolution of a zone plate scales linearly with its outermost zone width leads to high aspect ratios of the nanostructures. In the water window wavelengths region nickel is a well suited zone plate material, yielding high diffraction efficiency at moderate aspect ratios of the zones. Since it cannot be structured by reactive ion etching a tri-layer process making use of electrodeposition techniques was developed. All nickel zone plates presented in this work have demonstrated excellent first-order diffraction efficiencies at 2.4 nm wavelength. Zone plates with outermost zone widths of 40 nm, 30 nm and 25 nm were fabricated with the tri-level process yielding 21.6%, 18.0% and 14.7% first-order groove efficiency, respectively. These measured efficiencies correspond to maximum obtainable efficiencies determined by the galvanoform height of 100%, 95% and 85%.
1 citations
16 Sep 2011
TL;DR: A novel hard x-ray interferometer employing three optical Fresnel zone plates has been proposed in this article, which does not impose strong requirements on the coherence of the incident x-rays.
Abstract: A novel hard x‐ray interferometer employing three optical Fresnel zone plates has been proposed This amplitude‐division type interferometer does not impose strong requirements on the coherence of the incident x‐rays Employing a magnifying system can lead to increased spatial resolution for phase retrieval applications
1 citations
TL;DR: Recording data with a resolution of 5 or more bits appears to be the best way to construct high-quality images from computer-generated Fresnel holograms using a two-dimensional image as an object.
Abstract: We present a way of using a computer simulation to reconstruct gray-level images from computer-generated Fresnel holograms (Fresnel CGHs) using a two-dimensional (2D) image as an object. The interference fringes formed with spherical object waves emitting from 2D-image pixels and a plane reference wave were recorded as the sum of Fresnel zone plates at a CGH plane. It is assumed that the amplitude of the object wave is proportional to the pixel intensity of the 2D image. Reconstructed images from the Fresnel CGH are obtained by applying the fast Fourier transform algorithm to the Fresnel-Kirchhoff diffraction integral. The simulations were executed by changing parameters such as a bit number for CGH data recordings and a sampling interval of the interference fringes at the CGH plane, and some simulation results are presented; recording data with a resolution of 5 or more bits appears to be the best way to construct high-quality images.
1 citations
TL;DR: A theoretical model is established using Rayleigh-Sommerfeld diffraction theory to describe the diffraction focusing characteristics of low F-number diffractive optical elements with continuous relief fabricated by laser direct writing, and measurements made indicate that the spot size and diffraction efficiency coincide well with the theoretical results.
Abstract: A theoretical model is established using Rayleigh-Sommerfeld diffraction theory to describe the diffraction focusing characteristics of low F-number diffractive optical elements with continuous relief fabricated by laser direct writing, and continuous-relief diffractive optical elements with a design wavelength of 441.6nm and a F-number of F/4 are fabricated and measured to verify the validity of the diffraction focusing model. The measurements made indicate that the spot size is 1.75µm and the diffraction efficiency is 70.7% at the design wavelength, which coincide well with the theoretical results: a spot size of 1.66µm and a diffraction efficiency of 71.2%.
1 citations