X-Ray Lens Design

Fresnel zone plates and phase plates were developed for use with copper K-alpha X-rays (8 Kev λ = 1.54 Å). Alternating layers of transparent and opaque materials are sputtered onto a substrate, sliced perpendicular to the coating, thinned to a desired thickness and polished. Phase plates are made with a phase shifting layer in place of the opaque layers. Each material combination has a characteristic phase length, or thickness necessary to cause a relative phase shift of π between X-rays passing through the two materials. When phase plates are sliced to a thickness of integral multiple phase lengths, constructive interference occurs in the focal plane, with up to a four-fold increase in intensity compared to a zone plate. The design considerations and comparisons with experiment will be presented.