Resonantly enhanced transmission of terahertz radiation through a periodic array of subwavelength apertures

We demonstrate resonantly enhanced transmission of freely propagating coherent terahertz radiation through free-standing metal foils perforated with periodic arrays of sub-wavelength apertures. These arrays consist of 400 microm diameter apertures periodically spaced by 1 mm and 600 microm diameter apertures periodically spaced by 1.5 mm. We measure absolute amplitude transmission coefficients of ~0.6 at the resonance wavelength. Correspondingly, the ratio of the absolute amplitude transmission coefficient to the fractional aperture area at these resonance frequencies is ~5. This value at terahertz frequencies is significantly larger than equivalent values measured at optical frequencies.