Diffractive optics can be used to accurately control optical wavefronts, even in situations where refractive components such as lenses are not available. For instance, conventional Fresnel zone plates (ZPs) enable focusing of monochromatic radiation. However, they lead to strong chromatic aberrations in multicolor operation. In this work, we propose the concept of spatial entropy minimization as a computational design principle for both mono- and polychromatic focusing optics. We show that spatial entropy minimization yields conventional ZPs for monochromatic radiation. For polychromatic radiation, we observe a previously unexplored class of diffractive optical elements, allowing for balanced spectral efficiency. We apply the proposed approach to the design of a binary ZP, tailored to multispectral focusing of extreme ultraviolet (EUV) radiation from a high-harmonic tabletop source. The polychromatic focusing properties of these ZPs are experimentally confirmed using ptychography. This work provides a new route towards polychromatic wavefront engineering at EUV and soft-x-ray wavelengths.

中文翻译：

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量身定制用于多光谱刻印的极紫外聚焦光束的空间熵

即使在没有像透镜这样的折射组件的情况下，也可以使用衍射光学器件来精确地控制光波阵面。例如，常规的菲涅耳波带片（ZP）能够聚焦单色辐射。但是，它们在多色操作中会导致强烈的色差。在这项工作中，我们提出了空间熵最小化的概念，作为单色和多色聚焦光学器件的计算设计原则。我们表明，空间熵最小化会产生单色辐射的常规ZP。对于多色辐射，我们观察到以前未探索过的一类衍射光学元件，可实现平衡的光谱效率。我们将提出的方法应用于二进制ZP的设计，专门针对来自高谐波桌面源的极紫外（EUV）辐射的多光谱聚焦。这些ZP的多色聚焦特性是通过分型术通过实验确定的。这项工作为通向EUV和软X射线波长的多色波前工程提供了一条新途径。