Zone Plate Aperture Research Articles

Study of spatial resolution of circular and off-axis zone plates

The effect of limiting the zone plate aperture on its resolution was studied. Analytical formulas for calculating the field in the image plane were derived. The field distribution in the focal plane of circular and off-axis zone plates was numerically simulated.

Application Of Zone Plates To Alignment In X-Ray Lithography

Fresnel zone plate patterns, when printed on masks and wafers and suitably illuminated, form images that are useful for alignment in microlithography. These images are observed to be largely unaffected by poor edge definition or by pattern defects arising from variations in processing and linewidth control. This paper describes how these zone plates are used for automatic alignment in x-ray lithography. To obtain high contrast bright images with good signal-to-noise ratio (important in automatic alignment), the zone plates are illuminated with a collimated HeNe laser beam. The images formed at the focus are found to be nearly diffraction limited with diameters determined by the zone plate aperture ratio. With zone plates approximately 100 um in diameter and 300 um focal length, we have observed signal-to-noise ratios better than 20 dB and have been able to obtain position accuracies better than ±0.1 um. Our geometry is chosen so that magnification errors in the mask or wafer up to ~1 um are automatically compensated. A microprocessor-based system that performs all the alignment functions automatically is described.

Digital processing of images from a zone plate camera

A method for the digital decoding of data obtained with a gamma camera fitted with a zone plate aperture is described. Taking a line source as the object, computer simulations have been used to examine the effects of noise, solid angle variations, shape of detector and detector resolution and methods of dealing with these effects are considered. Using an Anger gamma camera and a zone plate aperture both a line source and a thyroid phantom containing 99Tcm have been well reconstructed. The behaviour of the system with regard to resolution, signal-to-noise ratio and tomographic capability is discussed.

Imaging in Nuclear Medicine with Incoherent Holography

One of the principal concerns in nuclear medicine is imaging the spatial distribution of tracer amounts of gamma emitting radiopharmaceuticals which have been intravenously administered to patients. These images are customarily formed on a gamma ray detector by means of lead pinholes or multichannel collimators. In practice these apertures yield only 1 cm spatial resolution and geometric efficiencies of 10-4. This paper describes the use of a lead Fresnel zone plate aperture in conjunction with an image intensifier camera to produce coded images of gamma sources. These images possess properties similar to holograms. This method shows promise of a factor of 4 or 5 improvement in resolution, a factor of 10 improvement in efficiency and gives 3 dimensional information about the object.