Fixing a diamond containing a high density of Nitrogen-Vacancy (NV) center ensembles on the apex of a multimode optical fiber (MMF) extends the applications of NV-based endoscope sensors. Replacing the normal MMF with a tapered MMF (MMF-taper) has enhanced the fluorescence (FL) collection efficiency from the diamond and achieved a high spatial resolution NV-based endoscope. The MMF-taper's high FL collection efficiency is the direct result of multiple internal reflections in the tapered region caused by silica, which has a higher refractive index (RI) than the surrounding air. However, for applications involving fluidic environments whose RI is close to or higher than that of the silica, the MMF-taper loses its FL collection significantly. Here, to overcome this challenge, we replaced the MMF-taper with an ultra-high numerical aperture (NA) microstructured optical fiber (MOF) which is tapered and sealed its air capillaries at the tapered end. Since the end-sealed air capillaries along the tapered MOF (MOF-taper) have isolated the MOF core from the surrounding medium, the core retains its high FL collection and NV excitation efficiency in liquids regardless of their RI values. Such a versatile NV-based endoscope could potentially find broad applications in fluidic environments where many biological processes and chemical reactions occur.

中文翻译：

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用于流体环境中基于氮空位集合的内窥镜的锥形超高数值孔径光纤尖端

将包含高密度氮空位 (NV) 中心集合的钻石固定在多模光纤 (MMF) 的顶点上，扩展了基于 NV 的内窥镜传感器的应用。用锥形 MMF (MMF-taper) 代替普通 MMF 提高了钻石的荧光 (FL) 收集效率，并实现了基于 NV 的高空间分辨率内窥镜。MMF-taper 的高 FL 收集效率是由二氧化硅引起的锥形区域多次内反射的直接结果，二氧化硅的折射率 (RI) 高于周围空气。然而，对于涉及流体环境的应用，其 RI 接近或高于二氧化硅的 RI，MMF 锥形会显着失去其 FL 收集。在这里，为了克服这一挑战，我们用超高数值孔径 (NA) 微结构光纤 (MOF) 替换了 MMF 锥形，该光纤是锥形的，并在锥形端密封其空气毛细管。由于沿锥形 MOF（MOF 锥形）的末端密封空气毛细管已将 MOF 核心与周围介质隔离，因此核心在液体中保持其高 FL 收集和 NV 激发效率，无论其 RI 值如何。这种基于 NV 的多功能内窥镜可能会在发生许多生物过程和化学反应的流体环境中得到广泛应用。无论液体的 RI 值如何，核心都保持其在液体中的高 FL 收集和 NV 激发效率。这种基于 NV 的多功能内窥镜可能会在发生许多生物过程和化学反应的流体环境中得到广泛应用。无论液体的 RI 值如何，核心都保持其在液体中的高 FL 收集和 NV 激发效率。这种基于 NV 的多功能内窥镜可能会在发生许多生物过程和化学反应的流体环境中得到广泛应用。