Advances in infrared and sub-millimeter filters

Infrared filters use a large variety of physical principles and techniques, as can be expected since they cover three decades of the IR spectrum (1 μm - 1 mm). The multilayer interference filters, derived from optical techniques, play the main role in the region 1 μm–40 μm. They have been successfully used in space applications. On the other side of the spectrum is the domain of metallic mesh filters, which is still developing. Bulk absorption, Reststrahlen bands, diffusion and gratings are also used to achieve the desired properties. A short review of this situation is given, with emphasis on the present trends and developments.Infrared and sub-millimeter filters use a large variety of physical principles and techniques that we may classify in two large families.