Topic
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: In this article, a modification of the Shack-Hartmann wavefront sensor was proposed, in which the lens array is made of Fresnel zone plates, which allows students to construct the sensor in an undergraduate laboratory at little cost.
Abstract: We propose a modification of the Shack–Hartmann wavefront sensor in which the lens array is made of Fresnel zone plates. The modification allows students to construct the sensor in an undergraduate laboratory at little cost. In spite of its simplicity the sensor has a sensitivity of λ∕50 in relative measurements, which is sufficient to measure a wavefront of a laser beam distorted by various optical elements as well as by a turbulent airflow. Such an experiment is an excellent supplement to a course in optics, gives students a deeper understanding of the wavefront concept, and demonstrates the wavefront measurement technique widely used in physics, astronomy, and medicine.
5 citations
16 Sep 2011
TL;DR: In this paper, a direct e−beam writing process of Fresnel zone plates (FZPs) using thick layers of PMMA resist as electroplating molds was reported.
Abstract: We report a direct e‐beam writing process of Fresnel zone plates (FZPs) using thick layers of PMMA resist as electroplating molds. We used 100‐kV electron beam lithography to directly expose thick PMMA layers, which were later used as plating molds without intermediate etching steps. High‐quality 500‐nm‐ and 1‐μm‐thick Au FZPs with outermost zone widths down to 50‐nm and 70‐nm, respectively, and with diameters up to 600 μm were fabricated. In this paper we present the details of the optimized fabrication process, such as development times, developer, dose tables, and line shrinkages required to obtain the desired zone widths and gaps between the zones. The diffraction efficiencies of the fabricated FZPs were measured for a wide range of x‐ray energies (2.8–13.2 keV) showing excellent values up to 65–75% of the theoretical maximum, reflecting the good quality of the FZPs. Spatially resolved diffraction efficiency measurements indicate the uniformity of the zone plates and lack of defects.
5 citations
TL;DR: In this article, a multi-regioned square zone plate (MRSZP) is presented which is achieved by sectioning a SZP into several regions, each region is composed of Fresnel zones in a way that the first zone of a given region is the same as the last zone of the previous ones, from transmission point of view.
Abstract: Multi-regioned square zone plate is presented which is achieved by sectioning a square zone plate into several regions. Each region is composed of Fresnel zones in a way that the first zone of a given region is the same as the last zone of the previous ones, from transmission point of view. By numerical studies and experimental works, we show capability of the proposed element in producing square corner-located focal points as well as square top hat-like beams. Additionally, we demonstrate that the distance between the generated points are a function of the number of the regions and the starting zone for sectioning the SZP. We have also illustrated that an array of focal points will also be accessible if the widths of all of the regions are the same.
5 citations
TL;DR: In this article, a Fresnel lens is designed and applied to modulate the light field into a uniform quadrangle or hexagon shape with controllable diameters by applying a spatial light modulator to load the phase information of the lens.
Abstract: Recently, annular beams have been developed to rapidly fabricate microscope tubular structures via two-photon polymerization, but the distribution of the light field is limited to a ring pattern. Here a Fresnel lens is designed and applied to modulate the light field into a uniform quadrangle or hexagon shape with controllable diameters. By applying a spatial light modulator to load the phase information of the Fresnel lens, quadrangle and hexagon structures are achieved through single exposure of a femtosecond laser. A 3×6 array of structures is made within 9 s. Comparing with the conventional holographic processing, this method shows higher uniformity, high efficiency, better flexibility, and easy operation. The approach exhibited a promising prospect in rapidly fabricating structures such as tissue engineering scaffolds and variously shaped tubular arrays.
5 citations
01 Mar 1974
TL;DR: In this article, a variety of closely related coded apertures, including an annulus, an inverted zone plate, a spiral zone plate and the Girard grill, are discussed.
Abstract: Mertz and Young introduced the idea of using a Fresnel zone plate as a shadow-casting reticle, or coded aperture, in x-ray astronomy. More recently, considerable progress has been made toward using the zone-plate aperture for gamma-ray imaging in nuclear medicine. The most successful configuration has used an off-axis section of a zone plate in conjunction with a halftone screen. In this paper, we discuss a variety of closely related coded apertures, including an annulus, an inverted zone plate, a spiral zone plate and the Girard grill. In most cases, the technique of grid-coded subtraction is used to suppress the zero-order (DC) background light usually associated with zone-plate imaging. The first application of this technique, reported by Stoner et al., used a sequence of two to four on-axis zone plates. In the present paper it is shown that the method can be extended to other apertures and is also very useful in synthesizing the spatial filters for optical decoding.
5 citations