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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TL;DR: The impact of Gaussian and fractal surface roughness on the exponent of power fall-off and the transition from coherent to incoherent scattering in radar sounding is shown and the Fresnel zone for planetary surfaces is derived.
Abstract: This paper reports the analysis of the geometric power fall-off of Fresnel zone scattering in radar sounding. Radar sounders can take advantage of strong coherent scattering from Fresnel zones at nadir which grow with sensor altitude. The strength of the signal and the actual rate of power fall-off, however, depend heavily on the surface properties. We first use the radar equation to separate geometric versus scattering mechanisms driving $R^{2}$ , $R^{3}$ , or $R^{4}$ fall-off. The Fresnel zone for planetary surfaces, where body curvature has an effect, is derived and its implications discussed. We show the impact of Gaussian and fractal surface roughness on the exponent of power fall-off and the transition from coherent to incoherent scattering. This is done in simulation and analytically to derive coherence loss functions. Finally, we study the effect of incoherent area fraction within the Fresnel zone. These results are intended to be used in radar link budgets, performance metrics, and scientific interpretation of sounding data.
45 citations
TL;DR: In this paper, the same authors used copolymer galvanoforms for nickel micro zone plates for high-resolution x-ray microscopy, achieving first-order diffraction efficiencies of up to 13% and 20%, respectively.
Abstract: High-resolution x-ray microscopy makes use of nanostructured diffractive optics such as Fresnel zone plates made of nickel. These micro zone plates are manufactured using microscopic galvanoforms and electrodeposition techniques. Copolymer galvanoforms for nickel micro zone plates were irradiated with high doses of x-ray radiation to increase the degree of cross-linking of the copolymer network; in this way, exact pattern replication in the galvanoform was obtained for zone aspect ratios of up to 8:1. Using these galvanoforms, nickel micro zone plates were produced for the soft x-ray wavelength λ=2.4 nm, with smallest zone widths of 30 nm and 40 nm, achieving first-order diffraction efficiencies of up to 13% and 20%, respectively.
45 citations
TL;DR: In this article, a simpler fiber design alternative to photonic crystal fibers is proposed for high-peak-power propagation with reduced nonlinear interactions, and multiple foci are observed in the far field.
Abstract: Propagation of light at 1.5 µm with peak intensity in an air hole is achieved within an air–silica-structured Fresnel waveguide. Thus a simpler fiber design alternative to photonic crystal fibers is possible for high-peak-power propagation with reduced nonlinear interactions. Multiple foci are observed in the far field.
45 citations
TL;DR: A new technique for precise focal-length measurement with a hologram is presented and offers the additional benefit of easy characterization by use of the same interferometer employed in examining the test optic.
Abstract: A new technique for precise focal-length measurements with a hologram is presented. This technique is widely applicable and is particularly useful for measuring large, slow lenses. In diffraction, the Fresnel-zone plate hologram emulates the reflective properties of a convex spherical mirror for use during transmission null tests of an optic by use of a phase-shifting interferometer. The hologram is written lithographically and therefore offers a higher degree of precision at a lower cost than its spherical mirror counterpart. A hologram offers the additional benefit of easy characterization by use of the same interferometer employed in examining the test optic. Better than ±0.01% precision is achieved during measurement of a 9-m focal-length lens by use of a 150-mm aperture interferometer.
45 citations
TL;DR: In this article, the spectral domain moment method was used to analyze homogeneous reflective phase shifters with conducting rings as elements, and numerical and experimental results were given for a novel phase correcting Fresnel zonal reflector based on this model.
Abstract: An array of conducting elements printed on a grounded dielectric substrate functions as an electromagnetic phase shifter. With a fixed substrate and a given operating frequency, the phase shift is determined by the array parameters. In the paper, the spectral domain moment method model for analyzing homogeneous reflective phase shifters with conducting rings as elements is presented, and numerical and experimental results are given. A novel phase correcting Fresnel zonal reflector based on this model is reported. A 43% maximum antenna efficiency and -22 dB sidelobe level were measured in X-band. The bandwidth of the reflector is estimated to be greater than 10%. >
45 citations