Terahertz near-field accumulation assisted by shape resonance in narrow rectangular apertures on metal film

We report huge field accumulations in rectangular aperture arrays on thin metal film by using shape resonance in THz frequency region. A large far-field transmittance enhancement is observed in the samples of various widths ranging from 10 μm to 1.8 μm which corresponds to only an order of λ/100. Theoretical calculations based on vector diffraction theory indicates 230 times field enhancement in the near-field for the 1.8 μm rectangular aperture.