Reflection suppression and absorption enhancement of optical field at thin metal gratings with narrow slits

Abstract

Optically thin metal gratings of high filling factor can support surface plasmon polariton modes at their horizontal metal boundaries and vertical cavity modes inside their slits. These modes are coupled through the metal stripes and the slits. This letter shows that the resonant interactions between the modes critically influence the optical field distribution near the grating and substantially enhance several phenomena such as low reflection, low transmission, and high absorption of the electromagnetic radiation. A high degree of energy confinement is obtained, especially when the energy is stored almost exclusively on the far side of the grating, away from the incident radiation. It is numerically shown that this phenomenon originates from the interaction of field modes with the collective motion of free electrons, as considered in the Drude model.

λ3/20000 plasmonic nanocavities with multispectral ultra-narrowband absorption for high-quality sensing

“…12,14 The cavity mode can support a narrow linewidth at a specific resonant wavelength related to the corresponding geometry of the cavity resonantor. 12,14,27 Even though the slit is ultra-narrow, the existence of FP cavity modes have been verified previously. 12,30 Therefore, based on the cavity resonance, near-unity light absorption can be achieved in this deep-subwavelength nanocavity.…”

“…19 The multiple narrow-band light absorption performance derives from the extremely enhanced optical field coupling and confinement in the metasurface due to the excitation of plasmon cavity modes and surface plasmon resonances. 12,14,[27][28][29][30] To confirm the mechanism of the multispectral narrowband light absorption, we calculated the electric and magnetic field distributions of the four absorption peaks k 1 -k 4 in Fig. 1(b).…”

“…2(a) and 2(b). These features arise from the excitation of plasmon cavity modes in the slits between adjacent paired patch tips 12,27,30 which can produce strong optical field coupling and enhancement. 12,14 The cavity mode can support a narrow linewidth at a specific resonant wavelength related to the corresponding geometry of the cavity resonantor.…”

“…2(c)) also confirms the formation of a plasmon cavity resonance. [27][28][29][30] At k 2 , main electric field is confined in the nanocavities between the large rectangular patches and a small electric field is distributed along the sides of patches (Fig. 2(d)).…”

Nearly perfect absorption in a single-layer metallic grating with rectangular grooves on its front surface

“…Agreeing with the results in Ref. [25], the absorptions of all the resonance modes in the above metallic grating are not larger than 50 %, when the coupling between the SPPs and the CMs occurs the absorption is slightly larger but not more than 75 % [30]. In order to further enhance the absorption, it is necessary to clarify the individual role of each resonance mechanism mentioned above.…”