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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14 Jun 2010
TL;DR: In this article, a tip-wave superposition method is proposed to model the scattered wavefield as the superposition of events multiply reflected and transmitted in accordance with the wavecodes, which allows modeling of selected events independently.
Abstract: Seismic waves traveling in the subsurface can be described by two physically different processes: propagation inside layers with smoothly varying properties and reflection and transmission at internal reflectors, which are formed by parameter discontinuities. Evaluation of the multiple reflections-transmissions for complex subsurface geometries is not straightforward. The presence of diffracting edges and vertices limits the applicability of geometrical seismics. Reflections-transmissions in the Fresnel zones near the shadow boundaries of the ray tubes can be described as the sum of geometrical seismic waves and diffracted waves in the boundary-layer approximation. To describe the reflection-transmission in the caustic zones caused by interface curvatures, we introduced the tip-wave superposition method. This method explicitly represents the scattered wavefield as the superposition of events multiply reflected and transmitted in accordance with the wavecodes, which allows modeling of selected events independently. Each event is formed by the sequential action of the propagator matrices inside heterogeneous layers with effective reflection and transmission coefficients at curved interfaces. Each element of the matrix contains the tip waves diverging from a small interface element. Effective coefficients generalize plane-wave coefficients used in the conventional seismic modeling for curved reflectors, non-planar wavefronts and finite frequencies.
5 citations
TL;DR: An experimental simulation of the use of the Shack-Hartmann wavefront sensor based on an array of electrically controlled zone plates made of ferroelectric domains to enhance astronomical images obtained by "Lucky Imaging" is presented.
Abstract: A modified Shack-Hartmann wavefront sensor based on an array of electrically controlled zone plates made of ferroelectric domains is presented. The camera used for image acquisition is also used for wavefront sensing. An experimental simulation of the use of this sensor to enhance astronomical images obtained by “Lucky Imaging” is presented.
5 citations
TL;DR: In this article, the spatiotemporal and spectral characteristics of ultrawide-band terahertz pulses after passing through a Fresnel lens are studied by using the scalar diffraction theory.
Abstract: The spatiotemporal and spectral characteristics of ultrawide-band terahertz pulses after passing through a Fresnel lens are studied by using the scalar diffraction theory. The simulation shows that the transmitted terahertz waveforms compress with increasing propagation distance, and the multi-frequency focusing phenomenon at different focal points is observed. Additionally, the distribution of terahertz fields in a plane perpendicular to the axis is also discussed, and it is found that the diffraction not only induces focusing on-axis but also inhibits focusing at off-axis positions. Therefore, the Fresnel lens may be a useful alternative approach to being a terahertz filter. Moreover, the terahertz pulses travelling as a basic mode of a Gaussian beam are discussed in detail.
5 citations
TL;DR: In this paper, the optimization of Fresnel zone plates using a genetic algorithm and a finite-difference time-domain simulator is studied, and the results are compared with a traditionally designed zone plate and a doubly hyperbolic lens.
Abstract: The optimization of Fresnel zone plates using a genetic algorithm and a the body-of-revolution, finite-difference time-domain simulator is studied. This technique is applied to zone plates for use in a free-space, focused-beam system to measure the electrical properties of materials. The results are compared with a traditionally designed zone plate and a doubly hyperbolic lens. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2223–2227, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24520
5 citations
TL;DR: In this article, a new physical theory of diffraction was proposed based on action at a distance, in which the reradiating molecules of a screen are treated as equivalent to a thin layer of half-wave dipoles, to which the Fresnel zone theory is applied.
Abstract: Some optical experiments, indicating that an illuminated edge acts in all directions like a linear radiator, are described. A new physical theory of diffraction is put forward based on action-at-a-distance, in which the re-radiating molecules of a screen are treated as equivalent to a thin layer of half-wave dipoles, to which the Fresnel zone theory is applied.
5 citations