Detection of strong light-matter interaction at the nano-scale in concealed optical cavities via a thermal transducer

A thin layer of a mid-IR transparent polymer is inserted inside a metallic optical nano-resonator, where a photonic mode and an intersubband transition are strongly coupled together. Acting as a non-perturbative transducer, and without modifying the optical response, the polymer allows the detection of absorbed optical power in the form of thermal expansion due to heat dissipation. This innovative approach permits to identify - even at the single nano-resonator level - the typical anti crossing characteristic of the polaritonic system, and to perform direct imaging of the electromagnetic fields buried within the inside of an otherwise inaccessible optical nanocavity.