Effective description of THz localized waveguide resonance through metal film with split ring resonator holes: zero refractive index.

Using a periodic array of split ring resonator holes within a terahertz range, we numerically and experimentally confirmed a zero refractive index at localized waveguide resonant frequency of aluminum film. The effective index was directly calculated from the phase difference of electromagnetic waves passing through film and air. Thickness-independent resonant frequency, as well as spatially static hole resonant modes, clearly verified a zero refractive index. For experimentation, we fabricated samples by means of a femtosecond laser machining system and employed a terahertz time domain spectroscopy system to measure transmitted terahertz pulses. Further, the effective index of refraction extracted from phases and amplitude of measured transmitted pulses confirmed a zero refraction index at resonant frequency.