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):