Fresnel zone

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

Methods of imaging, focusing and conditioning neutrons

Abstract: A compound refractive lens for neutrons is provided having a plurality of individual unit Fresnel lenses comprising a total of N in number. The unit lenses are aligned substantially along an axis, the i-th lens having a displacement t i orthogonal to the axis, with the axis located such that ∑ i = 1 N   t i = 0. Each of the unit lenses comprises a lens material having a refractive index decrement δ<1 at a wavelength λ<200 Angstroms. In a preferred mode, the lens above is configured such that the displacements t i are distributed and have a standard deviation σ t of the displacements t i about the axis, and wherein each of the unit lens has a smallest Fresnel zone width of s n −s n−1 , where s n and s n−1 are the zone radii of the n and n−1 zones and the standard deviation is σ t ≦[s n −s n−1 ]/4.

Hard X-ray microscopy activities at SPring-8

Abstract: Development of microfocusing optics for scanning microscopy and image forming optics for imaging microscopy are now in progress in SPring-8 by using varieties of optical devices: refractive lens, total reflection mirrors. Fresnel zone plates, and sputtered-sliced Fresnel zone plates. Spatial resolution of 100 nm has been achieved in scanning microscopy using highly coherent X-ray beam at a 248 m-long beamline 20XU and F2P' focusing optics. Recent results on development of optical systems are described.

Dynamic spectra of interplanetary scintillations

Abstract: Interplanetary scintillations (IPS) are fluctuations in the apparent intensity of radio sources caused by fluctuations in the electron density of the solar wind1. Observations at a single wavelength provide information on the spatial spectrum of electron density at scales of the order of the radius of the first Fresnel zone. However, dynamic spectra covering a wide range of wavelengths show evidence of fluctuations on a much larger scale2. Unfortunately, the problem of estimation of the spatial spectrum at this larger scale is analytically intractable. Here we compare the observations2 with a numerical simulation of the diffraction of plane waves by a two-dimensional random phase screen. The frequency–time structure of the simulated IPS shows good qualitative agreement with the observations when the turbulence spectrum in the phase screen is a simple power law with the Kolmogorov exponent. No ad hoc large-scale structure is necessary to account for the observations.

Fresnel zone laser coupling mirror

Abstract: A laser cavity includes a spherical mirror and a flat mirror, the flat mirror having a plurality of holes arranged in a Fresnel zone pattern so as to provide distributed output coupling having a near-field focal point; alternatively, the flat mirror may comprise a pattern of reflecting material on a light-transmissive medium.

Fresnel number of a regular polygon and slit.

Abstract: The concept of the Fresnel number is generalized to make it possible to describe the regular polygon and slit illuminated by a homogeneous plane wave. The generalization is based on nonlinear regression of the axial intensity distribution curve. A useful analytical expression for the Fresnel number is presented. A simple experiment to show the different Fresnel numbers in one observation plane is illustrated.