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Fresnel zone

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


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TL;DR: The paper presents an asymptotic expression of relative intensity distribution in a Fresnel diffraction pattern at an opaque straight strip illuminated with a spherical wave and shows sinusoidal behavior, which can be used in easy location of maxima or minima of the relative intensity.
Abstract: The paper presents an asymptotic expression of relative intensity distribution in a Fresnel diffraction pattern at an opaque straight strip illuminated with a spherical wave. The asymptotic expression is used in an analysis showing an area of validity where the asymptotic expression reduces to an asymptotic expression of relative intensity distribution in a Fresnel diffraction at a half plane. The area of validity is defined through width of the geometrical shadow in a Fresnel diffraction pattern at an opaque straight strip and distance of a point under study to the center of the Fresnel diffraction pattern. Within this area, relative intensity in the Fresnel diffraction pattern at an opaque straight strip shows sinusoidal behavior, which can be used in easy location of maxima or minima of the relative intensity. The result of the analysis is supported by experiments realized in the area of validity and outside it.

3 citations

Journal ArticleDOI
TL;DR: In this paper, it was shown that the average turbulence-induced bias in refraction angles depends on the radiation wavelength as lambda/sup(p/--4)/2, more or less ε/sup en-dash1/6/ for Kolmogorov turbulence.
Abstract: Two recent adjacently published papers on the average effects of turbulence in radio and optical occultation studies of planetary atmospheres appear to disagree on the question of wavelength dependence. It is demonstrated here that in deriving a necessary condition for the applicability of their method. Hubbard and Jokipii neglect a factor which is proportional to the square of the ratio of the atmospheric or local Fresnel zone radius and the inner scale of turbulence. They also fail to establish sufficient conditions, thereby omitting as a further factor the square of the ratio of atmospheric scale height and the local Fresnel zone radius. The total descrepancy, which numerically is typically within several orders of magnitude of 10/sup 11/ for radio and 10/sup 7/ for optical occultations, means that their results correspond to geometrical optics and not to wave optics as claimed. Thus their results are inherently inapplicable in a discussion of the wavelength dependence of any parameter, such as the bias in the average refraction angle treated by Eshleman and Haugstad. We note that for power spectra characterized by the (--p) exponent of the turbulence wavenumber, the average turbulence-induced bias in refraction angles depends on the radiation wavelength as lambda/sup( p/--4)/2,more » or as lambda/sup en-dash1/6/ for Kolmogorov turbulence. Other features of the Hubbard-Jokipii analysis are also discussed.« less

3 citations

Proceedings ArticleDOI
29 Nov 2007
TL;DR: In this article, the photonic sieve has been used as a novel diffractive optical element modulating either amplitude or phase which consists of a great number of pinholes distributed appropriately over the Fresnel zones for focusing and imaging of light.
Abstract: Photon sieve is a novel diffractive optical element modulating either amplitude or phase which consists of a great number of pinholes distributed appropriately over the Fresnel zones for the focusing and imaging of light. Photon sieve has the advantages of the diameter of pinholes beyond the limitation of the corresponding Fresnel zone width and the minimum background in the focal plane. Furthermore, photon sieve can be fabricated on a single surface without any supporting struts required unlike the Fresnel zone plate. Photon sieve can be used as EUV telescope for solar orbiter, space-based surveillance telescope operating at visible light, or other imaging components. Photon sieve can also be used as one of the promising lithographic tools for nanoscale science and engineering to obtain the lower cost, higher flexibility and better resolution. The approaches to enhancing imaging resolution of photon sieve are presented in detail. According to Fresnel-Kirchhoff diffraction theory, the diffractive field of photon sieve is described by means of the discrete fast Fourier transform algorithm. The related contents include the calculation of point spread function, the suppression of side lobes, the imaging bandwidth, the physical limit of resolution, and the diffraction efficiency. Imaging properties of photon sieve are analyzed on the basis of precise test.

3 citations

Journal ArticleDOI
TL;DR: In this article, the amplitude and arrival time statistics of very high frequency (50 kHz-2000 kHz) sound scattered from a rough wind-driven wave surface are modeled and the amplitude saturation occurs in the normalized second moment of acoustic intensity when the surface correlation length exceeds a Fresnel zone length.
Abstract: The amplitude, Doppler spread, and temporal coherence of VHF scattering is important for the performance of high frequency sonars and underwater communications systems in operating scenarios where energy from the sea surface cannot be screened. For this talk, the amplitude and arrival time statistics of very high frequency (50 kHz–2000 kHz) sound scattered from a rough wind-driven wave surface are modeled. Saturation occurs in the normalized second moment of acoustic intensity when the surface correlation length exceeds a Fresnel zone length. Fluctuations in arrival time do not saturate and increase proportionally to the dominant surface wave component. Data collected at 300 kHz agree with the model results. Energy is first detected in the wind-driven surface wave field at wavelengths of 1.7 cm and 3.4 cm. The former wave corresponds to a gravity-capillary wave whose phase speed is at a minimum. The principal appearance of this type of wave has threshold implications for the range of acoustic transmission frequencies susceptible to saturation in amplitude statistics.

3 citations

Journal ArticleDOI
TL;DR: A simple and reliable way of characterizing double-sided hard X-ray Fresnel zone plates by differential measurements with a Cu and an Ni filter is presented.
Abstract: Double-sided Fresnel zone plates are diffractive lenses used for high-resolution hard X-ray microscopy. The double-sided structures have significantly higher aspect ratios compared with single-sided components and hence enable more efficient imaging. The zone plates discussed in this paper are fabricated on each side of a thin support membrane, and the alignment of the zone plates with respect to each other is critical. Here, a simple and reliable way of quantifying misalignments by recording efficiency maps and measuring the absolute diffraction efficiency of the zone plates as a function of tilting angle in two directions is presented. The measurements are performed in a setup based on a tungsten-anode microfocus X-ray tube, providing an X-ray energy of 8.4 keV through differential measurements with a Cu and an Ni filter. This study investigates the sources of the misalignments and concludes that they can be avoided by decreasing the structure heights on both sides of the membrane and by pre-programming size differences between the front- and back-side zone plates.

3 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202326
202249
202137
202052
201965
201878