Theory of Light Scattering in Subwavelength Metallic Slot Antenna Array Fabricated on Subwavelength Thin Film

We demonstrate an analytic model that describes the near-field electromagnetic field profile near a subwavelength-sized metallic slot antenna fabricated on a thin dielectric substrate having a subwavelength thickness reaching λ/1000 in the terahertz frequency region. We found two-dimensional light diffraction induced by the two-dimensional nature of the slot antenna, and back-reflected waves interfered with each other in a complicated manner, resulting in a coupling of the Fourierdecomposed field amplitudes between the diffraction orders along the x and the y directions. We applied these findings to our model by modifying a previously developed model [D. J. Park et al., J. Korean Phys. Soc. 65, 1390 (2014)], and we monitor the effect on far-field transmission. This coupling effect was found to contribute to removal of physically-meaningless spikes or divergences in the transmission spectra, especially for relatively thick substrates.