One of the fundamental hurdles in plasmonics is the trade-off between electromagnetic field confinement and the coupling efficiency with free-space light, a consequence of the large momentum mismatch between the excitation source and plasmonic modes. Acoustic plasmons in graphene, in particular, have an extreme level of field confinement, as well as an extreme momentum mismatch. Here, we show that this fundamental compromise can be overcome and demonstrate a graphene acoustic plasmon resonator with nearly perfect absorption (94%) of incident mid-infrared light. This high efficiency is achieved by utilizing a two-stage coupling scheme: free-space light coupled to conventional graphene plasmons, which then couple to ultraconfined acoustic plasmons. To realize this scheme, we transfer unpatterned large-area graphene onto template-stripped ultraflat metal ribbons. A monolithically integrated optical spacer and a reflector further boost the enhancement. We show that graphene acoustic plasmons allow ultrasensitive measurements of absorption bands and surface phonon modes in ångström-thick protein and SiO₂ layers, respectively. Our acoustic plasmon resonator platform is scalable and can harness the ultimate level of light–matter interactions for potential applications including spectroscopy, sensing, metasurfaces and optoelectronics.

等离子体激元的基本障碍之一是电磁场限制与自由空间光的耦合效率之间的权衡，这是激发源和等离子体激元之间动量不匹配的结果。尤其是石墨烯中的声等离激元具有极高的场约束水平以及极高的动量失配。在这里，我们表明可以克服这种基本的折衷，并证明石墨烯声等离子体激元谐振器对入射的中红外光具有近乎完美的吸收（94％）。这种高效率是通过利用两阶段耦合方案实现的：将自由空间光耦合到常规的石墨烯等离子体激元，然后将其耦合到超限声等离子体激元。为了实现这个方案，我们将无图案的大面积石墨烯转移到模板剥离的超扁平金属带上。单片集成的光学垫片和反射镜进一步增强了该功能。我们表明，石墨烯声等离激元可以对ångström厚蛋白和SiO中的吸收带和表面声子模式进行超灵敏的测量分别为₂层。我们的声波等离子体共振器平台具有可扩展性，可以利用光-物质相互作用的最高水平，用于光谱，传感，超表面和光电等潜在应用。