Fresnel zone

About: Fresnel zone is a research topic. Over the lifetime, 2337 publications have been published within this topic receiving 37650 citations.

Two-point Ray Tracing In 3-D Complex Media Using Triangular Surfaces: Application to Line-drawing Migration In 3-D

Abstract: This expanded abstract presents and discusses a two-point (nonzero offset: source-receiver) ray tracing scheme for 3D complex seismic horizons discretized via triangles. The fast and robust method, based on Fermat’s stationary principle, was first introduced by Guiziou (1991). The two successive steps of the scheme called atomic and quadratic step, search the ray with a minimum (resp. maximum) traveltime. We have added a third step for improving the ray accuracy without discretizing surfaces via too small triangles. Resulting rays are validated by carefully checking the signature of the rays. The global algorithm allows to compute reflected, refracted and diffracted raypaths with a minimum computational time if the size of unit triangles of the interfaces equals the radius of their associated Fresnel zone. Events have been picked on ECORS 2.5-D deep seismic reflection stack volume (Marthelot et al., 1994) and reorganized to construct horizons discretized via triangles whose vertices are the picked events (time structures). Depth structures are inferred from the combination of two complementary approaches: migrating the line-drawing (time structures) by the above ray tracing scheme following a top down procedure. refining the model deduced from the migration of the linedrawing by forward modeling (calculating traveltimes) for time sections and shotpoints.

Dynamic phase control by rigid spiralized Fresnel zone plates

Abstract: Compact Fresnel lensing has been extensively used to achieve efficient management of the optical front. The further ability of dynamic tunability generally requires geometric reshaping through elastic deformations. Spiralized lens devices are able to present this property thanks to their substructured elongated configuration; nevertheless, elasticity is still subject to unavoidable limitations due to the limited flexibility of adoptable materials; thus, a nonflexible variant of these structures is quite more convenient. Here we describe a way to promote dynamic continuous light transmission through synchronous displacements of rigid spirals. The general design theory is explained to show the versatility of this new technology. A special study is devoted to the promotion of a controllable phase delay device, based on the Fresnel zone plate design, to promote perfectly endless and continuous linear phase transitions.

Geophysical surveying using fresnel pilot signals

Abstract: In seismic geophysical surveying, a servo-controlled vibrator is driven by a pilot signal that corresponds generally to the variations in density that are encountered in scanning at a constant rate along a radial segment of a Fresnel zone plate, and the resulting seismic waves that arrive at a spaced receiver are recorded as a conventional variable density trace. The pilot signal is thus one that becomes self-compressing by the diffraction of monochromatic light to a focal point on the axis of the zone plate. Accordingly, illumination of the recorded variable density trace by monochromatic light effectively time-compresses each repetition of the pilot signal in the recorded trace by producing in the plane of the Fresnel zone plate focus a concentration of illumination that represents by its intensity and position the amplitude and travel time of seismic wave energy from the vibrator to the receiver by a particular path. In practice, any pilot signal for which the frequency varies linearly with time is so closely similar to a true Fresnel signal that it focuses monochromatic light in the same way.

Fresnel's rings in reconstruction of scattering media holograms

Abstract: The theoretical description of the field reconstructed from an in-line hologram of dispersed media is presented. The intensity distribution in the focal plane of a lens placed behind a hologram is analyzed. It is shown that two overlapped patterns are observing in this plane. The first pattern is entirely in accordance with the small-angle spectrum of radiation scattered by the ensemble of particles, and its view does not depend on the distances between the particles, the hologram, and the lens. The second pattern is made of Fresnel’s rings and depends on the distance between the particles and the hologram. A statistical interpretation of the distribution of intensity in the focal plane of a lens is proposed. Experimental results and discussion are presented.

Effect of optical elements of transmitter on intensity beam profile

Abstract: The paper deals with the Fresnel diffraction effect which occurs when the laser beam is transmitted by the free space optical link transmitter. A specific diffraction problem of the spherical wave with the Gaussian intensity distribution is explained. The paper is focuses on the experimental study of diffraction in the Fresnel zone (the near zone of radiation).