We have seen in Sec. 4.4 that x-ray lenses with good efficiency are theoretically possible, if one keeps the maximum thickness small by breaking the lens up into Fresnel zones and varies the material thickness in each zone in such a way that the desired phase delay between 0Â° and 360Â° is obtained. However, it is difficult to produce the desired thickness profile within each zone with the precision and resolution required for the x-ray region.
A simplified Fresnel lens can be realized if one simply blocks of the radiation from the zones with the wrong phase with a ring of absorbing material. Such a lens consists essentially of an opaque screen with openings for those areas that contribute in phase at the desired image point
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