We report the design and realization of the back focal plane (BFP) imaging for the light emission from a tunnel junction in a low-temperature ultrahigh-vacuum (UHV) scanning tunneling microscope (STM). To achieve the BFP imaging in a UHV environment, a compact “all-in-one” sample holder is designed and fabricated, which allows us to integrate the sample substrate with the photon collection units that include a hemisphere solid immersion lens and an aspherical collecting lens. Such a specially designed holder enables the characterization of light emission both within and beyond the critical angle and also facilitates the optical alignment inside a UHV chamber. To test the performance of the BFP imaging system, we first measure the photoluminescence from dye-doped polystyrene beads on a thin Ag film. A double-ring pattern is observed in the BFP image, arising from two kinds of emission channels: strong surface plasmon coupled emissions around the surface plasmon resonance angle and weak transmitted fluorescence maximized at the critical angle, respectively. Such an observation also helps to determine the emission angle for each image pixel in the BFP image and, more importantly, proves the feasibility of our BFP imaging system. Furthermore, as a proof-of-principle experiment, electrically driven plasmon emissions are used to demonstrate the capability of the constructed BFP imaging system for STM induced electroluminescence measurements. A single-ring pattern is obtained in the BFP image, which reveals the generation and detection of the leakage radiation from the surface plasmon propagating on the Ag surface. Further analyses of the BFP image provide valuable information on the emission angle of the leakage radiation, the orientation of the radiating dipole, and the plasmon wavevector. The UHV–BFP imaging technique demonstrated here opens new routes for future studies on the angular distributed emission and dipole orientation of individual quantum emitters in UHV.

中文翻译：

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低温超高真空扫描隧道显微镜中隧道结光发射的后焦平面成像

我们报告了低温超高真空（UHV）扫描隧道显微镜（STM）中隧道结光发射的后焦平面（BFP）成像的设计和实现。为了在 UHV 环境下实现 BFP 成像，我们设计并制造了一种紧凑的“一体式”样品架，它使我们能够将样品基底与光子收集单元集成在一起，其中包括半球固体浸没透镜和非球面收集单元镜片。这种专门设计的支架可以表征临界角以内和之外的光发射，并且还有助于在特高压室内进行光学对准。为了测试 BFP 成像系统的性能，我们首先测量银薄膜上的染料掺杂聚苯乙烯珠的光致发光。在 BFP 图像中观察到双环图案，由两种发射通道产生：分别在表面等离子体共振角周围的强表面等离子体耦合发射和在临界角处最大化的弱透射荧光。这样的观察还有助于确定 BFP 图像中每个图像像素的发射角，更重要的是，证明了我们的 BFP 成像系统的可行性。此外，作为原理验证实验，电驱动等离子体发射被用来证明所构建的 BFP 成像系统用于 STM 诱导电致发光测量的能力。BFP 图像中获得了单环图案，揭示了在 Ag 表面传播的表面等离子体激元泄漏辐射的产生和检测。对 BFP 图像的进一步分析提供了有关泄漏辐射的发射角、辐射偶极子的方向和等离子体激元波矢量的有价值的信息。这里展示的 UHV-BFP 成像技术为未来研究 UHV 中单个量子发射器的角分布发射和偶极子方向开辟了新途径。