Stacked Multilevel Fresnel Zone Plates for Hard X-Rays
  The new type of multilevel Fresnel zone plate, consisting of stacked layers with bi-level zone profile has been investigated. The conditions of layers acting as single multilevel Fresnel zone plate have been discussed by numerical simulation. The criteria for layers alignment have been presented. Considered approach of zone plate fabrication allows achieving high level focusing efficiency from one side and decreasing zone profile etching deep from the other. 
L. Haroutunyan, K. Trouni, A. Kuyumchyan
physics.optics