尖端增强纳米腔中红外-可见和频产生的原位调控
In-operando control of sum-frequency generation in tip-enhanced nanocavities
AI总结：
本文利用金属扫描探针尖端增强镜上纳米颗粒腔，实现连续波和频产生并原位调控，增强达14个数量级，为少分子非线性纳米光学研究提供了通用平台。
摘要：
和频产生（SFG）是一种二阶非线性过程，广泛用于以单层灵敏度表征表面和界面。近年来，等离激元纳米腔中的光场增强已使连续波（CW）激光能够从纳米尺度分子区域产生SFG，有望实现纳米尺度SFG光谱学以及用于可见频率中红外探测的相干上转换等应用。在此，我们展示了当单个镜上纳米颗粒（NPoM）腔置于金属扫描探针尖端下方时产生的连续波SFG；该NPoM腔在可见频率处共振，并填充有单层分子。尖端作为高效的宽带天线，将入射的连续波红外照明聚焦到纳米腔上。NPoM纳米腔内的级联近场增强在宽红外频率范围内产生非线性光学响应，实现了高达14个数量级的SFG增强。此外，尖端的纳米机械定位允许通过调节局部场增强而非照明强度来实现SFG的原位调控。尖端增强纳米腔的多功能性使得无需复杂制造双共振纳米腔即可在少分子体系中对多种分子物种进行SFG研究。我们的结果还预示着尖端在其顶点提供强可见和红外场增强的SFG纳米成像，为未来非线性纳米光学应用提供了一个稳健的平台。
英文摘要：
Sum-frequency generation (SFG) is a second-order nonlinear process widely used for characterizing surfaces and interfaces with monolayer sensitivity. Recently, optical field enhancement in plasmonic nanocavities has enabled SFG with continuous wave (CW) lasers from nanoscale areas of molecules, promising applications like nanoscale SFG spectroscopy and coherent upconversion for mid-infrared detection at visible frequencies. Here, we demonstrate CW SFG from individual nanoparticle-on-mirror (NPoM) cavities, which are resonant at visible frequencies and filled with a monolayer of molecules, when placed beneath a metal scanning probe tip. The tip acts as an efficient broadband antenna, focusing incident CW infrared illumination onto the nanocavity. The cascaded near-field enhancement within the NPoM nanocavity yields nonlinear optical responses across a broad range of infrared frequencies, achieving SFG enhancements of up to 14 orders of magnitude. Further, nanomechanical positioning of the tip allows for in-operando control of SFG by tuning the local field enhancement rather than the illumination intensities. The versatility of tip-enhanced nanocavities allows for SFG studies of a wide range of molecular species in the few-molecule regime without the need for complex nanofabrication of doubly-resonant nanocavities. Our results also promise SFG nanoimaging with tips providing strong visible and IR field enhancement at their apex, offering a robust platform for future applications in nonlinear nanooptics.
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