Effect of the subwavelength hole symmetry on the enhanced optical transmission through metallic films

Abstract

We present here the measurements on the extraordinary optical transmission when light passes through different subwavelength hole arrays fabricated on a 120-nm-thick gold film by the focused ion beam system. The comparison of optical transmission shows that the aperiodic concentric circular hole arrays, which possess the sixfold rotational symmetry and central-inversion symmetry, have higher transmittance (about six and two times larger in peak intensity, respectively) than the periodic hexagonal and square lattice of hole array structures. This phenomenon can be attributed to the stronger constructive interference of multiple scattered waves in a higher symmetrical hole array structure. In addition, although the three structures possess the same lattice constant 1μm and hole diameter 350nm, the enhanced transmission peak for the circular hole arrays locates in the visible region, while that of the two periodic structures is in the infrared region. Moreover, when the hole diameter decreases, the transmission peak shifts slightly, while the transmittance drops rapidly.