Abstract
Tailoring radiative properties of a surface has become achievable with the fast advances in micro/nanofabrication and understanding in physical mechanisms [1]. The key is the interplay between electromagnetic fields of radiation and wavelength-comparable dimensions of periodic microstructures at surfaces. For example, gratings composed of periodic lines or wires aligned laterally on a substrate have been widely employed as polarizers and wavelength-selective filters [2]. A type of slit arrays, complex grating, was recently proposed and investigated with is componential gratings [3]. Their reflectance spectra at oblique incidence showed several due to Wood’s anomaly and “pseudoanomalies.”This work continues to study their infrared transmittance both numerically and experimentally at normal incidence. An objective is to seek the possibility in tailoring mid-infrared transmittance spectra with slit arrays of synthesized profiles. Another is to link some commonly-shared features in spectra with the profile similarity. Both directional and hemispherical transmittance spectra of slits on a silicon substrate are investigated in a broad band (2.5 um to 25 um). All numerically-obtained data are from programs based on the rigorous coupled-wave analysis while an FT-IR spectrometer is employed for measuring directional transmittance. Unique features in spectra are explained and many are elucidated with distributions of electromagnetic fields in the near field. Some transmittance dips through the complex slit array can also be attributed to pseudoanomalies, which are from its component slits. Though the thickness of a semi-transparent supporting substrate dominates the transmittance usually, numerical results here further confirm its little impacts on pseudoanomalies.