Abstract
A metasurface consisting of an infinite array of square loops was designed for maximal absorptivity for s-polarized light at a wavelength of 10.6 µm and 60 degrees off-normal. We investigate the effects of array truncation in finite arrays of this design using far-field FTIR spectroscopy and scattering scanning near-field optical microscopy. The far-field spectra are observed to blue-shift with decreasing array size. The near-field images show a corresponding decrease in uniformity of the local electric field amplitude and phase spatial distributions. Simulations of the far-field absorption spectra and local electric field are consistent with the measured results.
Highlights
Optical metamaterials are an engineered class of materials which exhibit properties not typically found in nature
We investigate the effects of array truncation in finite arrays of this design using far-field FTIR spectroscopy and scattering scanning near-field optical microscopy
The interaction of a beam of light of finite size can cause an equivalent form of array truncation if the number of illuminated elements is small compared to the number necessary for the desired optical property to converge to that of an infinite array
Summary
Optical metamaterials are an engineered class of materials which exhibit properties not typically found in nature. Metasurfaces and other sub-wavelength periodic structures are almost universally simulated as infinite arrays along the directions of periodicity, by considering a single unit cell with the appropriate boundary conditions. This greatly reduces the computational effort for simulation and is a good approximation for most applications. The interaction of a beam of light of finite size can cause an equivalent form of array truncation if the number of illuminated elements is small compared to the number necessary for the desired optical property to converge to that of an infinite array. It is clear that below some threshold the finite size of truncated arrays will significantly alter the device performance in terms of the near- and far-field response
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