Showing papers on "Zone plate published in 1968"

Holographic lens with aberration correction

Abstract: A technique for holographically constructing a lens made of stacked Fresnel zone plates on a thick emulsion photographic film which is capable of imaging a wide object field by joining the individual fields of each superimposed Fresnel zone plate to form an unaberrated composite image. The extent of the individual zone plate field is determined by the emulsion thickness and optical construction geometry and thereby allows restriction of this field to a size capable of unaberrated imaging.

Fresnel Zone Plate Antenna

Abstract: The paper describes the design of a Fresnel zone plate suitable for use as an antenna in the centimetric or lower wavelength range. It has been shown that such antennas can be fabricated by using either metal or dielectric rings. Its properties have been analysed by employing the simple methods of electromagnetic diffraction. Experimental results are reported showing close agreement with the theory. A theory has been presented explaining the working of the dielectric ring zone plate. The investigation leads to the conclusion that both the metal and dielectric zone plates are useful as low gain antennas.

Synthesis of fresnel diffraction patterns by overlapping zone plates.

Abstract: It has been shown previously that two overlapping circular zone plates will create the image of two separate zone plates, two circular dots of light, with the closeness of the dots proportional to the degree of overlap of the zone plates. It is shown here that more complicated patterns can be produced by superpositioning of zone plate sections if the zone plates are cut so that the same number of sections overlap in each area.

X-ray picture of the sun taken with fresnel zone plates.

Abstract: It is well known that Fresnel zone plates act as a lens with a focal length inversely proportional to the wavelength. At Professor Moellenstedt’s Institute of Applied Physics in Tubingen, a technique has been developed to manufacture micro-zone plates electronoptically from Buckbee-Mears zone plates. These micro-zone plates have a diameter of 0·5 mm approximately, 38 zones and a focal length of 30 cm for X-rays of nearly 50 A. Their resolving power is of the order of a few seconds of arc (Einighammer et al, 1966). One finds, however, experimentally as well as theoretically that the sharply defined image is surrounded by a halo having a diameter of a few minutes of arc for the above-mentioned zone plates. Whereas for a point source the intensity of a halo is poor and therefore unimportant, for extended sources it becomes large as a result of the superposition of the contributions from the individual points of the source. This has been demonstrated by the photometer curves of the images of circular sources by Einighammer (1966) (Figure 1). The halo is not noticeable in case of very narrow sources (curves a and b). With increasing diameter of the source the intensity of the halo rapidly increases (curves c and d). For the same source the brightness distribution of the halo agrees practically with the one obtained by a pinhole camera, provided the diameter of the hole and that of the zone plate are equal; these brightness distributions are represented by the dashed lines c′d′ in Figure 1.

Three-dimensional camera

Abstract: A three-dimensional hologram producing camera utilizing a single lens system for providing a volumetric image on bulk sensitive film having a zone plate positioned in front of the lens to provide greater resolution to the recorded image point formed as a volumetric biconically shaped light distribution in the film bulk.

New Techniques in X-Ray Astronomy

Abstract: A review is given of some modern developments in X-ray astronomy. Improved designs of proportional counters and other detectors are described. We further enumerate developments in solar X-ray spectrographs and heliographs, like the ‘gutter’ spectrograph, and the paraboloidal-hyper-boloidal frustrum mirror system, the zone plate technique. We also give a review of instruments and collimating techniques for the detection of non-solar celestial X-ray sources.