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. 2018 Jun 17;25(Pt 4):1048–1059. doi: 10.1107/S1600577518007208

Figure 4.

Figure 4

While there might be practical limitations to the number of zone plates Inline graphic that can be stacked together, one can obtain gains in first-order diffraction efficiency Inline graphic that go well beyond the simple thin zone plate expression of equation (1). In (a) we show the efficiency as a function of individual zone plate thickness Inline graphic and cumulative thickness t, where Inline graphic = Inline graphic zone plates are used with with a separation of Inline graphic = 10 µm (for Inline graphic = 45 µm, and Inline graphic = 25 nm for the first zone plate at 10 keV). A single gold zone plate with the optimum thickness Inline graphic = 2.0 µm would give Inline graphic = 32.7%, whereas much higher efficiencies can be obtained by using many more zone plates with slightly higher cumulative thickness. In (b) we show how the stacking of Inline graphic = 8 zone plates, each with a thickness Inline graphic = 0.5 µm, leads to differences in diffraction efficiency as one changes the separation distance Inline graphic between zone plates. Smaller separation distances Inline graphic are preferable but might be impractical, but even with larger separation distances like Inline graphic = 1000 µm one can still obtain an efficiency of Inline graphic = 36% if Inline graphic = 5 zone plates are used. All calculations were for gold zone plates at 10 keV.