Transmission forbiddance and absorption enhancement in a subwavelength metallic cross-slit

This paper investigates the transmission properties of a normally incident transverse magnetic (TM) wave through a single subwavelength metallic cross-slit (a vertical slit modified by a horizontal cut at the center of the slit). The results show that, as the horizontal cut length increases, the odd modes of the extraordinary optical transmission (EOT) of the slit exhibit an apparent red shift while the wavelengths of the even modes remain almost unchanged. If the horizontal cut length is large enough so that a red shifted odd mode degenerates with an even mode, the transmission is unexpectedly suppressed to nearly zero, at the same time an increased absorption (up to 85%) occurs. The behaviors of the excited surface plasmon polaritons (SPPs) inside the cross-slit are analyzed in detail. It is found that the interference between the encountering even mode and odd mode leads to the suppressed transmission and enhanced absorption.