AN INVESTIGATION OF FRESNEL AND FIRST ORDER ZONE PLATES

Equivalent First Order and Fresnel zone plates were constructed using a novel rotating wheel technique which allowed for convenient control of the modulation factor and simplified the problem of producing First Order and Fresnel zone plates which were equivalent. Using a microphotometer system, the focal plane diffraction patterns of both types of zone plates were quantitatively examined and compared as the modulation strength and recording linearity were varied. The effects of removing the amplitude transmission function, thereby producing a phase zone plate (by bleaching the photographic plates), were also noted, as were the effects of varying the number of zones in the zone plate. The Fourier relationship between the two types of zone plates was experimentally verified, as was the theoretical equality of intensity of all the sub-foci of the Fresnel zone plate. A phase shift was shown to exist at the focal point and at all axial nulls for both types of zone plates, using a modified Rayleigh interferometer. An examination of the properties of a 'one-step zone plate' yielded some interesting information concerning the thin transmittance type of hologram. (Author)