Designing objects with predefined optical properties is a task of fundamental importance for nanophotonics, and chirality is a prototypical example of such a property, with applications ranging from photochemistry to nonlinear photonics. A measure of electromagnetic chirality with a well-defined upper bound has recently been proposed. Here, we optimize the shape of silver helices at discrete frequencies ranging from the far-infrared to the optical band. Gaussian process optimization, taking into account also shape derivative information on the helices scattering response, is used to maximize the electromagnetic chirality. We show that the theoretical designs achieve more than 90% of the upper bound of em-chirality for wavelenghts 3 μm or larger, while their performance decreases toward the optical band. We fabricate and characterize helices for operation at 800 nm and identify some of the imperfections that affect the performance. Our work motivates further research both on the theoretical and fabrication sides to unlock potential applications of objects with large electromagnetic chirality at optical frequencies, such as helicity filtering glasses. We show that, at 3 μm, a thin slab of randomly oriented helices can absorb 99% of the light of one helicity while absorbing only 10% of the opposite helicity.

中文翻译：

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朝向光学频率下的最大电磁手性散射体

设计具有预定义光学特性的物体是纳米光子学的一项基本任务，手性是这种特性的典型例子，其应用范围从光化学到非线性光子学。最近提出了一种具有明确上限的电磁手性测量方法。在这里，我们在从远红外到光学波段的离散频率优化银螺旋的形状。考虑螺旋散射响应的形状导数信息的高斯过程优化用于最大化电磁手性。我们表明，对于 3 μm 或更大的波长，理论设计实现了超过 90% 的手性上限，而它们的性能向光学波段降低。我们制造并表征了在 800 nm 下运行的螺旋，并确定了一些影响性能的缺陷。我们的工作激发了在理论和制造方面的进一步研究，以解锁在光学频率下具有大电磁手性的物体的潜在应用，例如螺旋滤光玻璃。我们表明，在 3 μm 处，随机取向的螺旋薄板可以吸收一个螺旋的 99% 的光，而仅吸收相反螺旋的 10%。