SCATTERING MATRIX-METHODS FOR FAR-INFRARED METAL MESH FILTERS

The spectral transmission of inductive metal mesh of grid constant 50.8-mu-m and of several Fabry-Perot-filters made from the same mesh were measured in the wavenumber range from 50 cm-1 to 250 cm-1. A concise scattering matrix method is used to predict the transmission of the Fabry-Perot-filter from the spectrum of the constituent mesh. The calculation predicts the experimental transmission well in the diffraction-free region, but it was found that the theoretical spacer-thickness of the Fabry-Perot-Filter is systematically greater than the real, experimental spacer-thickness. The transmission characteristic of metal mesh on one surface of a dielectric sheet and of metal mesh between two dielectric sheets is shifted to smaller wavenumbers. Rescaling the wavenumber with the index of refraction yields the amount of the shift. In these cases only a modified scattering matrix calculation predicts some characteristics of the experimental results.