Fresnel zone

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

Extension of Fresnel Near-Field Region by Single-Cycle Sinusoidal Pulses

Abstract: : A circular conducting disk antenna is excited by three uniform current waveforms namely, a very high frequency CW sin& , a single-cycle sinwO1, and a single-cycle coswOt. The energy per cycle associated with each of these waveform is taken to be the uM. From the behavior of the radiated energy densities along the axis of the disk, it is found that if the CW waveform extends the near field to unit distance, then the corresponding distances are 1. 375 and 3.75 for the single-cycle sinwOt and the single-cycle coswOt respectively. These results show that the method of energy transfer to a large distance along the axis of an aperture (or disk) becomes more efficient when a short pulse, instead of a CW source, is applied. This will have applications wherever a transmission of high intensity beam of energy far away from a radiating device is needed.

Control of Spatial Distribution of Broadband Terahertz Radiation Using Fresnel Zone Plates

Abstract: The controllability of the directional pattern of separate frequency components of the broadband terahertz radiation spectrum by introducing Fresnel zone plates into the beam is shown.

Distinguishing characteristics of diffractive optical elements and Fresnel lenses

Abstract: Transmissive optical components tend to be classified as either diffractive or refractive, based on which phenomenon more accurately describes the way they function. Although their optical functions are governed by distinct physical phenomena, Fresnel lenses are often confused or conflated with Diffractive Optical Elements (DOEs) like Fresnel zone plates and kinoforms; this is due to their similarities in shape, the method of defining their surfaces, and even the name. This research was conducted as an opportunity to describe the distinguishing characteristics of DOEs and Fresnel lenses, as well as the acceptable terminology to use with both classes of optics. First, background on diffraction and geometrical optics will be discussed, followed by methods used to design and fabricate both types of elements. Then, back focal distance metrology is performed to demonstrate the difference in function. The experiment performed supports the fact that DOEs and Fresnel lenses are not the same. This work is intended as a clarification of nomenclature and functionality, as well as an illumination of what makes DOEs and Fresnel lenses distinct.

Correcting the secondary focus of Fresnel zone plate antennas

Abstract: The large aperture Fresnel zone plate antenna has been extensively investigated in recent years for application at frequencies from the microwave range to the terahertz region. These zone plate antennas have a focal length (F) and diameter (D) that are comparable (F/D = 0.3 to 2.5). The results of these investigations show that the phase-correcting zone plate gives performance comparable to a true lens. There is one limitation, however, in that most cases a secondary focus occurs on-axis at one-third the focal distance from the zone plate. The intensity is 10 dB or more down from the main focus. A method has now been developed to essentially eliminate this secondary focus by properly adjusting the amount and location of the phase-correcting grooves or rings. A revised positioning of the grooves and degree of correction can reduce the secondary focus, but maintain the integrity of the main focus. Specific examples have been analyzed and will be presented at the conference.

Use of optical masers in displays and printers.

Abstract: : The immediate purpose of this study is to develop laser technology for computer input output devices, and tore a laboratory type demonstration to indicate the ability to modulate electronically and deflect a light beam. This task is preparatory to further development of a complete laser display system. The deflection of laser beams using digital light deflectors and conical refraction, and the focusing of laser beams with a Fresnel zone lens were investigated. The results indicate that laser beams can be accurately deflected by means of a digital light deflector. Conical refraction shows promise for analog deflection of the beam and the Fresnel zone plate lens, when constructed with proper electrodes, is suitable for focus/defocus control. The conclusion indicates that digital electro-optic deflection of intense light beams is feasible and could lead to the realization of practical laser display and printing apparatus.