Nanoparticle-on-mirror cavity: a historical view across nanophotonics and nanochemistry

Pushing the limit of squeezing the light into the deep-subwavelength regime can serve as a holy grail for various applications, which are based on light–matter interactions. Especially, the advancements of spectroscopy, which is the foundation of the wide range of fundamental and practical studies, can be a representative example toward this end. Over the last decade, it turned out that a nanoparticle-on-mirror (NPoM) cavity can approach the ultimate limit of light squeezing. Particularly, a picocavity whose mode volume can be reduced to a dimension of a single atom was experimentally proved with a gold NPoM; thus, sub-molecule-level spectroscopy becomes available. This considerable progress has not been achieved alone with nanophotonic cavity science; nanochemistry has cooperatively played an important role in this way. Herein, I briefly review the historical development benchmarks of NPoM cavities with an integrative viewpoint across nanophotonics and nanochemistry. This review I believe can not only deepen the insight into the NPoM cavities but also envision the future directions of the relevant fields.