Quasi-single-order focusing zone plate with trapezoidal transmittance
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摘要: 为改进用于X射线聚焦的二值化Gabor波带片目前所存在的结构复杂、不利于加工制作的问题，在不改变梯形透过率函数的前提下，通过将传统的梯形孔基元变为平行四边形基元应用于波带片的设计之中，提出了一种聚焦效率更高的具有准单级聚焦特性的波带片。理论推导显示，该波带片除了像Fresnel波带片一样能够消除偶数级的焦点外，还可以消除3q级（q为整数）的焦点，1/m4（m为焦点级数）的效率衰减系数也使得高级衍射得到了很好的抑制。MATLAB数值模拟的结果证明，该波带片的特性不仅满足以上推论，还具有比Fresnel波带片和环带扇形基元阵列波带片更低的背景噪声，可以看作是一种准单级聚焦的新型波带片。此外，在同一波带内，这种基于平行四边形基元孔的波带片设计的透光区始终保持各处的径向宽度为该波带的一半，且扇区结构简单一致，能够降低不少加工难度，易于推广应用。Abstract: We designed a novel zone plate by employing the trapezoidal transmission function. Numerical simulations based on Fresnel-Kirchhoff diffraction theory have demonstrated the quasi-single-order focusing characteristic and different performance of this plate from Fresnel zone plate. The comparison with a binary Gabor zone plate shows that the first-order diffraction efficiency of this plate is about 11.3% higher. Besides, all foci with orders of 2q and 3q(q=1,2,3,) are eliminated for this plate, and the diffraction efficiency of the fifth order is only 1/625 of the first order theoretically. More importantly, due to its symmetric structure and duplicable sectors that have equal width in a half-wave zone, this plate is much easier for nanofabrication.
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Key words:
- zone plate /
- quasi-single-order focusing /
- diffraction efficiency /
- duplicable sectors
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