Figure 6
Simulated wavefield intensity in the vicinity of the focal spots created by two stacked zone-doubled FZPs with an outermost zone width of [\Delta r] = 25 nm. (a) When two FZPs of identical diameter, D = 45 µm, are stacked, the separation distance required for an acceptable focal spot shape is below ld = 10 µm. (b) The separation distance can be relaxed by adjusting the diameter, D2, of the second FZP. For a separation distance of ld = 25 µm an optimal focus profile is recovered for a diameter D2 = 44.8 µm.  [article HTML]