Department of Imaging Physics , Delft University of Technology , NL-2600 GA Delft , The Netherlands.
Nano Lett. 2018 Oct 10;18(10):6107-6112. doi: 10.1021/acs.nanolett.8b00546. Epub 2018 May 2.
Many applications in (quantum) nanophotonics rely on controlling light-matter interaction through strong, nanoscale modification of the local density of states (LDOS). All-optical techniques probing emission dynamics in active media are commonly used to measure the LDOS and benchmark experimental performance against theoretical predictions. However, metal coatings needed to obtain strong LDOS modifications in, for instance, nanocavities, are incompatible with all-optical characterization. So far, no reliable method exists to validate theoretical predictions. Here, we use subnanosecond pulses of focused electrons to penetrate the metal and excite a buried active medium at precisely defined locations inside subwavelength resonant nanocavities. We reveal the spatial layout of the spontaneous-emission decay dynamics inside the cavities with deep-subwavelength detail, directly mapping the LDOS. We show that emission enhancement converts to inhibition despite an increased number of modes, emphasizing the critical role of optimal emitter location. Our approach yields fundamental insight in dynamics at deep-subwavelength scales for a wide range of nano-optical systems.
许多（量子）纳米光子学中的应用都依赖于通过对局部态密度（LDOS）进行强的纳米级修饰来控制光物质相互作用。探测有源介质中发射动力学的全光技术通常用于测量 LDOS，并根据理论预测对实验性能进行基准测试。然而，为了在例如纳米腔中获得强 LDOS 修饰，所需的金属涂层与全光特性化不兼容。到目前为止，还没有可靠的方法来验证理论预测。在这里，我们使用聚焦电子的亚纳秒脉冲穿透金属，并在亚波长共振纳米腔内部的精确定义位置激发埋置的有源介质。我们以深亚波长的细节揭示了腔体内自发发射衰减动力学的空间布局，直接绘制了 LDOS。我们表明，尽管模式数量增加，但发射增强会转化为抑制，这强调了最佳发射体位置的关键作用。我们的方法为广泛的纳米光学系统在深亚波长尺度下的动力学提供了基本的见解。
