Far-IR optical properties of freestanding and dielectrically backed metal meshes

The optical properties of freestanding and dielectrically backed inductive metal meshes are investigated in the far IR spectral regime. The most pronounced effect of the substrate is to cause a shift in the diffraction edge to longer wavelengths by a factor equal to the substrate index of refraction. Various theoretical models are reviewed and tested with the main result being that only the microwave based waveguide-array model successfully predicts the freestanding and dielectrically back optical features in and around the diffraction edge. A simplified version of this model is presented and shown to be adequate for describing the majority of the spectral features. The backed meshes are then characterized in terms of mirror quality for use in optically pumped far IR lasers.