Abstract

The main elements of an infrared interference filter are the substrate, the main filter stack and the necessary blocking filter stacks. These latter stacks are placed either upon a separate substrate or on the reverse of the main filter substrate. In the 8-13 micrometer wavelength band the substrate will normally be germanium or zinc-selenide, and typical stacks consist of zinc-sulphide or -selenide/thorium-fluoride or lead-telluride/zinc-sulphide alternating layers. The choice of substrate depends upon the subsequent application of the filter, and in many cases it is desirable to have a substrate with a very low index of refraction, i.e. air. When we consider the total physical thickness of a typical stack combination to be in the region 30 - 100 micrometers, it is tempting to have a possibility for making a self-supporting or pellicle type of filter.

© 1984 Optical Society of America