Directional and hemispherical mid-infrared transmittance through microscale slit arrays on a semi-transparent substrate at normal incidence

Abstract

The directional and hemispherical transmittance through four microscale slit arrays on a semitransparent substrate were investigated at normal incidence. Materials and vertical dimensions of all arrays were the same, but lateral dimensions varied among the three simple slit arrays. The complex slit array had three identical slits and three lamellae of dissimilar widths in a profile period. The incidence covered a broad-band mid-infrared region (2.5–25μm) in which two linear polarizations were considered. Impacts of the structure profile, incidence polarization and wavelength, and optical constants of involved materials on spectra were studied numerically with programs based on the algorithm termed rigorous coupled-wave analysis (RCWA). Near-field patterns of electromagnetic fields that correlated with unique transmittance were also plotted to identify responsible physical mechanisms. In addition, the directional transmittance spectra of fabricated samples were measured with FT-IR spectrometry. Reasonable agreement between numerical and experimental results was obtained. Unique features in spectra were consistently found, regardless of the finite substrate thickness.