Helmholtz-like Nanoresonators Applied to Surface Enhanced Infrared Absorption

Nanostructures exhibiting high electric field enhancement are very appealing for infrared spectroscopic applications. The optical Helmholtz resonator presents very high enhancement factors within hot volumes. Nevertheless, its nanofabrication is rather challenging and has hindered its practical use. Here, we introduce and study, both theoretically and experimentally , a simplified nanostructure that supports an Helmholtz-like resonance with the expected high electric field enhancement. This resonator is then applied to the SEIRA detection of 2,4-dinitrotoluene, leading to reflectivity changes up to 15% at λ = 6.6 µm.