We have analyzed and characterized a terahertz stacked holes array over a broad transmission bandwidth. In this context, we identify the key contributions of the surface plasmon modes related to the periodicity of array, and of the subcut off transmission through the holes responsible of a ground left-handed dispersion branch. The experimental verification of a multimode electromagnetic behavior is performed by time domain spectroscopy, with a complementary assessment by full-wave analysis. A circuitlike approach appears suitable for the understanding of a zero-gap transition between the left- and right-handed characteristics, opening the way of nonvanishing group velocity in a near-zero index propagation medium. Such a balanced composite operation, pointed out over the past in the dual element transmission line approaches, is thus generalized for a stacked subwavelength holes array, whose operation can be compared to the one of the so-called fishnet structures.
We report on angle-resolved time domain spectroscopy (TDS) carried out on a prismlike negative index metamaterial operating around 0.5 THz. The wedge-type devices are constituted of hole arrays etched in gold thin films, which are stacked according to a sequential mask shift. By means of a goniometric TDS setup and subsequent analysis of the temporal waveforms, negative refraction is demonstrated with values close to n=−1 around 0.5 THz. The dispersion of refractive index retrieved from the Snell–Descartes law shows comparable trends in comparison with the dispersion deduced from complex transmission and reflection measurements on slab-type samples.
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