Microscopes and various forms of interferometers have been used for decades in optical metrology of objects that are typically larger than the wavelength of light λ. Metrology of sub-wavelength objects, however, was deemed impossible due to the diffraction limit. We report the measurement of the physical size of sub-wavelength objects with deeply sub-wavelength accuracy by analyzing the diffraction pattern of coherent light scattered by the objects with deep learning enabled analysis. With a 633 nm laser, we show that the width of sub-wavelength slits in an opaque screen can be measured with an accuracy of ∼λ/130 for a single-shot measurement or ∼λ/260 (i.e., 2.4 nm) when combining measurements of diffraction patterns at different distances from the object, thus challenging the accuracy of scanning electron microscopy and ion beam lithography. In numerical experiments, we show that the technique could reach an accuracy beyond λ/1000. It is suitable for high-rate non-contact measurements of nanometric sizes of randomly positioned objects in smart manufacturing applications with integrated metrology and processing tools.

中文翻译：

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亚波长物体的深亚波长非接触式光学计量

数十年来，显微镜和各种形式的干涉仪已用于通常大于光波长λ的物体的光学计量。然而，由于衍射极限，亚波长物体的计量被认为是不可能的。我们通过分析由具有深度学习能力的分析对象散射的相干光的衍射图案，报告了具有深亚波长精度的亚波长对象物理尺寸的测量。使用 633 nm 激光器，我们表明可以以 ~ λ /130的精度测量不透明屏幕中亚波长狭缝的宽度（对于单次测量）或 ~ λ/260（即 2.4 nm），当结合距物体不同距离处的衍射图案的测量时，从而挑战扫描电子显微镜和离子束光刻的准确性。在数值实验中，我们表明该技术可以达到超过λ /1000的精度。它适用于具有集成计量和处理工具的智能制造应用中随机定位物体的纳米尺寸的高速非接触式测量。