Custom Infrared Lens, thermal imaging cameras & systems components

What materials are suitable for infrared lenses?
When designing infrared optical components, various factors
related to the optical materials used must be considered. These factors include
refractive properties, optical transmission, non-thermal properties,
hardness/durability, environmental sensitivity, weight/density, manufacturing
technology, and cost. Some of these factors are still interrelated. For
example, for some materials, their optical transmittance is high at room
temperature, but decreases at higher temperatures. Considering all these
factors, when designing infrared optical components, careful consideration of material
selection is required. Available materials are: germanium (Ge), silicon (Si),
gallium arsenide (GaAs) and cadmium telluride (CdTe); zinc compounds, such as
zinc sulfide (ZnS) and zinc selenide (ZnSe); water-soluble crystals, such as
Potassium bromide (KBr), sodium chloride (NaCl) and potassium chloride (KCl);
fluorides such as magnesium fluoride (MgF2), calcium fluoride (CaF2) and barium
fluoride (BaF2); and other materials, Such as fused silica and sapphire;
chalcogenide glass, etc. The currently available materials are as follows (blue
is chalcogenide glass):
