Fresnel zone

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

Super-Fresnel resolution of plasma inhomogeneities by electromagnetic sounding

Abstract: The application of the double weighted Fourier transform (DWFT) method is suggested for extracting the linear integral of the electron density in the inhomogeneous plasma from microwave or IR sounding data. The virtue of DWFT is its ability to localize the measured linear integral in the area, narrow as compared with the radius of the Fresnel zone, that is to realize super-Fresnel resolution. The advantages of the DWFT method are illustrated, firstly, by numerical simulation of a wave propagation through the Gaussian inhomogeneity in conditions of weak scattering, when a small angle Born approximation is applicable, and secondly, by theoretical estimates of resolution in conditions of strong scattering. The method under discussion promises to be helpful for studying the fine structure of turbulent plasma.

Parallel maskless optical lithography for prototyping, low-volume production, and research

Abstract: Earlier we reported on a proof-of-concept maskless-lithography system that used an array of Fresnel zone plates to focus multiple beams of 442 nm light onto a substrate, and micromechanics for multiplexing light to the several zone plates, enabling patterns of arbitrary geometry, at 350 nm linewidth, to be written. We referred to the technique as zone-plate-array lithography (ZPAL). We also demonstrated zone-plate-array microscopy. Here, we report on a “preprototype” ZPAL system operating at an exposure wavelength of 400 nm, capable of quick-turn-around, maskless lithography. We describe the lithography results with this system as well the development of high-speed data delivery systems, high-numerical-aperture zone plates (up to 0.95), and a multiplexing scheme that will enable us to move to a “full-prototype” system capable of 210 nm feature sizes at a moderate but useful throughput of ∼0.25 cm2 in 20 min.

Wind and refractive-turbulence sensing using crossed laser beams.

Abstract: The theory of optical propagation through atmospheric turbulence demonstrates the sensitivity of such quantities as log-amplitude variance and covariance to strength of refractive turbulence and transverse wind. We exploit this sensitivity by using a crossed-path technique to derive path profiles of these quantities. The results are insensitive to changes in the spatial spectrum of the refractive-index variations. The path resolution is easily varied by changing the receiver and transmitter separations and is ultimately limited by signal-to-noise considerations. The experimental results for horizontal paths, described here, will ultimately be used to indicate the feasibility of profiling on vertical paths with passive sources.

Resolving Power in Diffraction Microscopy with Special Reference to X-Rays

Abstract: ROGERS'S1 elementary explanation of Gabor's2 technique for microscopy treats the hologram as a generalized Fresnel zone plate. I have used this idea for deriving a resolution criterion. Two point objects separated by a distance y produce two Fresnel zone patterns at the hologram with centres separated by a distance z, where z = pay/(Pa − qa), if Pa and qa are the distances from the illuminating point source of wave-length λa to the hologram film and from the film to the object, respectively. The subscript a refers to parameters of the ‘analysis’ while r will refer to the ‘reconstruction’.

Sub-25-nm laboratory x-ray microscopy using a compound Fresnel zone plate

Abstract: Improving the resolution in x-ray microscopes is of high priority to enable future applications in nanoscience. However, high-resolution zone-plate optics often have low efficiency, which makes implementation in laboratory microscopes difficult. We present a laboratory x-ray microscope based on a compound zone plate. The compound zone plate utilizes multiple diffraction orders to achieve high resolution while maintaining reasonable efficiency. We analyze the illumination conditions necessary for this type of optics in order to suppress stray light and demonstrate microscopic imaging resolving 25 nm features.