Anomalous near-perfect extraordinary optical absorption on subwavelength thin metal film grating.

We demonstrate analytically and numerically that the anomalous extraordinary optical absorption through thin metal grating with air slit arrays can be excited simultaneously by long and short range surface plasmonic modes supported on the surfaces of thin metal film in weak coupling while this absorption can only be excited by short range surface plasmonic mode in strong coupling. In particular, we predict localized plasmonic mode inside air slits holding double-effect to generate the anomalous extraordinary optical absorption when only this mode is present and to suppress this absorption when the pathways excited by localized and surface plasmonic modes are present simultaneously. Furthermore, we present that double-layer metal grating consisting of two identical single-layer metal gratings can be exploited to enhance absorption efficiency more than 99% and 90% for excited localized plasmonic modes and surface plasmonic modes respectively.