Surface plasmon mediated transmission of subwavelength slits at THz frequencies

We present measurements and a numerical modeling that elucidate the role of surface plasmons in the resonant transmission of a subwavelength slit in a conducting material. By using THz time domain spectroscopy, we determine the Fabry-Perot transmission resonances for a single slit formed from a wafer of a semiconductor with a surface plasma frequency in the THz frequency range. We measure large redshifts in the resonant frequencies close to the surface plasma frequency, which are 50% lower than the resonance frequencies expected well below the surface plasma frequency. This is an effect attributed to the coupling of plasmons on the adjacent surfaces of the slit.