Fresnel zone

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

Recent progress in X-ray optics at the ESRF

Abstract: It is the task of x-ray optics to adapt the raw beam generated by modem sources such as synchrotron storage rings to a great variety of experimental requirements in terms of intensity, spot size, polarization and other parameters. The very high quality of synchrotron radiation (source size of a few microns and beam divergence of a few micro-radians) and the extreme x-ray flux (power of several hundred Watts in a few square mm) make this task quite difficult. In particular the heat load aspect is very important in the conditioning process of the brute x-ray power. Cryogenically cooled silicon crystals and water-cooled diamond crystals can presently fulfil this task, but limits will soon be reached and new schemes and materials must be envisioned. A major tendency of instrument improvement has always been to concentrate more photons into a smaller spot utilizing a whole variety of focusing devices such as Fresnel zone plates, refractive lenses and systems based on bent surfaces, for example Kirkpatrick-Baez systems Apart from the resistance of the sample, the ultimate limits are determined by the source size and strength on one side, by materials properties, cooling, mounting and bending schemes on the other side. and fundamentally by the diffraction process. There is also the important aspect of coherence that can be both a nuisance and a blessing for the experiments, in particular for imaging techniques. Its conservation puts additional constraints on the quality of the optical elements. A review of recent progress in this field is given.

Reconstructed images from volume holograms in the Fraunhofer approximation: Analysis by a new spherical-wave expansion

Abstract: The “circular plane-wave” expansion of a spherical wave is newly proposed, and the reconstructed images from volume holograms are studied analytically by applying this method to the expansion of the object wave. The analysis is performed on the weakly coupled amplitude holograms in the Fraunhofer approximation. Both the amplitude and phase of the reconstructed waves are modulated, except the case of exact reconstruction, and are determined by recording and reconstruction parameters and the hologram thickness. The amplitude modulation by the volume hologram of a semitransparent object causes the space-variant or the space-invariant bandpass filtering effect by the spherical-wave or the plane-wave illumination of the object, respectively. The phase modulation causes aberrations and becomes small for a hologram having the large thickness.

Radio Propagation Calculation: A Technique Using 3D Fresnel Zones for Decimeter Radio Waves on Lidar Data

Abstract: This article discusses the Fresnel radio tool (FRT) model for radio-coverage prediction based on the Fresnel-zone calculation. The 3D Fresnel zones are calculated from the transmitter (Tx) source to each cell on a raster digital map. For numerical calculation purposes, Fresnel zones are cross sectioned to a finite number of fragments. The attenuation and phase shift of each segment can be adjusted according to the obstacle type. At the target receiver (Rx) point, contributions from each fragment, represented by complex numbers, are summed and converted to a signal strength.

Statistical Aspects of Sound Propagation in the Ocean

Abstract: A tutorial review of sound propagation in a random ocean is presented, with emphasis on the oceanography and the statistics of received signals. The list of references should help the reader who wishes to investigate further specific aspects of the problem.