近日，西班牙巴斯克地区大学Rainer Hillenbrand团队研究了尖端增强纳米腔中和频率产生的操作控制。该项研究成果发表在2025年5月22日出版的《光：科学与应用》杂志上。

和频生成（SFG）是一种二阶非线性过程，广泛用于表征具有单层灵敏度的表面和界面。最近，等离子体纳米腔中的光场增强使来自纳米级分子区域的连续波（CW）激光器的SFG成为可能，这是纳米级SFG光谱和相干上转换等有前景的应用，用于可见频率的中红外检测。 

研究组展示了单个纳米颗粒在镜面（NPoM）腔上的CW SFG，当放置在金属扫描探针尖端下方时，这些腔在可见频率下共振，并填充有单层分子。尖端充当高效的宽带天线，将入射的CW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范围的红外频率上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不是照明强度来操作控制SFG。尖端增强纳米腔的多功能性允许在少分子范围内对各种分子物种进行SFG研究，而不需要复杂的纳米制造。该研究结果还承诺，SFG纳米成像的尖端在其顶点提供强大的可见光和红外场增强，为非线性纳米光学的未来应用提供了一个强大的平台。

附：英文原文

Title: In-operando control of sum-frequency generation in tip-enhanced nanocavities

Author: Roelli, Philippe, Pascual Robledo, Isabel, Niehues, Iris, Aizpurua, Javier, Hillenbrand, Rainer

Issue&Volume: 2025-05-22

Abstract: 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. 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.

DOI: 10.1038/s41377-025-01855-5

Source: https://www.nature.com/articles/s41377-025-01855-5