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 mum diameter apertures periodically spaced by 1 mm and 600 mum diameter apertures periodically spaced by 1.5 mm. We measure absolute amplitude transmission coefficients of similar to 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 similar to 5. This value at terahertz frequencies is significantly larger than equivalent values measured at optical frequencies. (C) 2004 Optical Society of America.