Terahertz near-field imaging of metallic subwavelength holes and hole arrays

Metallic microstructures are investigated by time-resolved terahertz near-field imaging. By our approach, we can directly follow field diffraction from subwavelength structures as well as coupling to the surface. Near-field images of the spectral amplitude and phase of the electric field show the formation, propagation, and attenuation of surface waves and allow us to distinguish between propagating and stationary modes. Our results show that the field enhancement in an individual hole, together with the formation of standing waves on the metal surface between the holes, are key mechanisms for the extraordinary transmission phenomenon through periodic hole arrays. (C) 2008 American Institute of Physics.