The peak at the high energy side in the strong coupling phenomenon was observed to converge toward the peak energy at the shoulder of the transmittance spectrum T (λ ). This takes place regardless of the thickness of SiO 2 film. In addition, the peaks on the low-energy side are converging, corresponding to the absorption peak of SiO 2 . For this reason, when SiO 2 is used as a dielectric in MIM, a gap region is formed between 1052 cm -1 (9.51 µm) and 1217 cm -1 (8.22 µm) where the resonance spec-trum cannot exist. Also the peak intensity of (1 -R) is twice less than that of pure CaF 2 peaks. Note, that from 8-to-14 µm is the wavelength region for optical window in the mid-IR. Therefore, pure SiO 2 as dielectric layer disturb the efficient photo-thermal energy conversion. In the case of pure (100%) SiO 2 , a small absorption peak around 800 cm -1 is also observed to be coupled with the meta-surface, but the effect becomes smaller as the amount of SiO 2 decreases. After 50% of SiO 2 (about 125 nm in thickness), these small peaks cannot be observed and, ultimately, only the two prominent absorption peaks appear to be coupled with the meta-surface. A plot showing the respective peak intensities is shown along-side with the mapping data (Fig. ).