We demonstrate subwavelength axial sectioning on biological samples with a stimulated emission depletion (STED) microscope combined with supercritical angle fluorescence (SAF) detection. SAF imaging is a powerful technique for imaging the membrane of the cell based on the direct exploitation of the fluorophore emission properties. Indeed, only when fluorophores are close to the interface can their evanescent near-field emission become propagative and be detected beyond the critical angle. Therefore, filtering out the SAF emission from the undercritical angle fluorescence (UAF) emission in the back focal plane of a high-NA objective lens permits nanometer axial sectioning of fluorescent emitters close to the coverslip. When combined with STED microscopy, a straightforward gain in axial resolution can be reached without any alteration of the STED beam path. Indeed, STED-SAF implementation only requires a modification in the detection path of the STED microscope and thus could be widely implemented.

中文翻译：

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超临界角荧光在 STED 显微镜下增强轴向切片

我们展示了使用受激发射损耗 (STED) 显微镜结合超临界角荧光 (SAF) 检测对生物样品进行亚波长轴向切片。SAF 成像是一种强大的技术，用于基于对荧光团发射特性的直接利用来对细胞膜进行成像。事实上，只有当荧光团靠近界面时，它们的渐逝近场发射才能传播并在临界角之外被检测到。因此，从高 NA 物镜后焦平面中的下临界角荧光 (UAF) 发射中滤除 SAF 发射允许靠近盖玻片的荧光发射器的纳米轴向切片。当与 STED 显微镜结合使用时，在不改变 STED 光束路径的情况下，可以获得轴向分辨率的直接增益。事实上，STED-SAF 的实施只需要修改 STED 显微镜的检测路径，因此可以广泛实施。