Fresnel zone

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

A novel phase retrieval technique based on propagation diversity via a dielectric slab.

Abstract: This paper deals with a novel technique to determine the far field of an aperture starting from the knowledge of two near-field intensity data sets collected over the same measurement plane. The diversity between the two intensity data sets is achieved by ensuring different conditions of the near field propagation between the aperture and the measurement plane. In particular, one measurement is performed under free-space propagation condition while the second one is performed by exploiting a dielectric slab, with known properties, filling partly the space between the aperture and the measurement plane. A phase retrieval technique, that faces a non linear inverse problem, is solved by assuming as unknown the plane wave spectrum of the aperture field. The feasibility of the novel approach is presented also in comparison with the usual near field phase retrieval technique exploiting measurements of the near field intensity over two scanning planes.

About the method of integral field representation as the double weighted Fourier transform in the problems of wave propagation in inhomogeneous media

Abstract: The limits of applicability of the method of integral field representation as the double weighted Fourier transform (DWFT) are determined on the basis of an exact path representation for the Green function of the parabolic equation. The estimates we have obtained imply that the DWFT method takes into account the effects of diffraction by inhomogeneities with scales equal to or less than the radius of the first Fresnel zone of a plane wave and can be exploited to solve the inverse problems of retrieval of the inhomogeneous-medium parameters from the data measured in the source and receiver planes.

Simulation of Tight Focusing of Laser Light by Gold Zone Plate

Abstract: In this paper amplitude Fresnel zone plates with gold relief on silica glass is investigated by using frequency dependent finite difference time domain method. During the simulation linearly and circularly polarized Gaussian beams with wavelength of 532 nm are proposed as incident light. Study of the focal spot characteristics versus the relief height of zone plate is carried out. It shows that the height of 140 nm allows to achieve an optimal ratio between width and intensity of the focal spot. Also, it is shown that for linear polarized Gaussian beam this gold zone plate gives tighter focal spot with the full width at half maximum of 0.38λ and 0.86λ than phase zone plate and produce circle focal spot with the Cartesian axis diameter of 0.64λ for circularly polarized light.

3D Radiating and Focusing Antenna System

Abstract: The 3D antenna system focusing the radiation in a far zone based on the linear array consisting of declining semitransparent plane arrays is examined in paper. The quasioptical conditions are fulfilled for the system's geometry. The distance between separate elements of system satisfies to the Fresnel zone conditions, and the radiation pattern (RP) of system is calculated in its far zone. The separation of variables is assumed in the apertures of separate elements and in the RP's components. The explicit formulas are derived for the field values in the constituent elements of antenna and created RP. The ability of system to create the RPs of the different kind is supported by computations.