Fresnel zone

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

Single element plate lens

Abstract: PURPOSE:To obtain the single element plate lens with a high numerical aperture which converges laser light into a fine spot by forming a fine striped pattern like a hologram lens and a Fresnel lens on both surfaces of a transparent plate. CONSTITUTION:A hologram or Fresnel zones 2 and 3 are formed on both surfaces of the transparent plate 1. Incident laser light (a) is converged through the striped pattern 2 toward a point P as a light beam (b) and the numerical aperture sintheta1 at this time is 0.2-0.3 at most. Then, it is converged on a point Q as a light beam C through the striped pattern 3 and the numerical aperture sintheta2 is increased to about 0.5, but the striped pattern 3 operates as a lens with a 0.2- 0.3 numerical aperture to the light beam (b), and aberrations are reduced enough to ignore.

Intracavity optical modulation using Fresnel zone-plate-type E-O lens

Abstract: Setting an electrically controllable dual focal-point (DFP) lens into the optical resonator of a laser, we can readily modulate the output power of the optical beam with a relatively low voltage. The DFP lens is fabricated by combining an electro-optic (E-O) material with the Fresnel zone-plate (FZP) lens, in which numerous transparent (ITO) electrodes are evaporated in the form of the Fresnel zone- plate (FZP) on a PLZT ceramic E-O plate to compose a dual focal-point lens with and without an applied voltage. In addition, the PLZT (La/Zr/Ti equals 9/65/35) ceramic used here as an E-O material represents a quadratic E-O effect. Inserting this DFP E-O lens inside the optical resonator of an He-Ne 3.39 mm laser on trial, the fundamental modulation characteristics are investigated. As a result, about 15.5% modulation degree was obtained with applying the rf (2 kHz) voltage of 13.5 V p under a certain bias. The operational principle is experimentally demonstrated together with theoretical discussions.

Method of evaluation of radiation fields in Fresnel region for circular and elliptic aperture antennas

Abstract: A method of evaluating Fresnel zone radiation fields is studied for circular and elliptic aperture antennas which is illumated with an arbitrary aperture distributions. Fresnel zone field is represented by a series of generalized Lommel functions of two parameters defined here. It is shown that the generalized Lommel functions with any degrees and orders may be derived from the original Lommel functions [1] using the recurrence relations. The validity of the expressions is verified numerically by comparing with those obtained from the method by Sun and Rusch [2] and from direct numerical integrations. This method may also be applied to predict the far field pattern of offset typed parabolic reflector antennas [3]. The three dimensional pictures of Fresnel patterns for circular apterute with tapered illumination as well as uniform distribution are obtained.

Analysis and design of Fresnel zone plates with multiple foci

Abstract: Fresnel Zone Plates (FZPs) become an interesting alternative to traditional lenses when planar fabrication is advantageous, and are used in a wide range of physical disciplines such as optics, microwave propagation, or ultrasounds. Conventional FZPs produce a single focus, which is optimal in most applications. However, certain medical applications, such as MRI (magnetic resonance imaging) guided ultrasound surgery, require multiple foci ultrasound exposures. In this work, new multi-focus Fresnel lenses (MFFLs) based on conventional FZPs are presented. The advantages and drawbacks of these new MFFL structures are thoroughly analyzed. There is a tradeoff on the number of foci achieved in a single MFFL and its focusing efficiency. Therefore, the most efficient MFFL is that with two foci. A procedure for designing 2-foci MFFLs, in which the focal length of both foci may be selected independently, is established. For each 2-foci MFFL, there are several physical implementations. The focusing properties of all ...