Germanium for many years has been the prevailing material in infrared equipmentis.
The reduction in cost appeared recently in uncooled thermal imagers and peculiarly in uncooled detectors either bolometer or ferroelectric give to the cost of the Germanium optics an increased relative importance.
Obviously it has been researched ways to reduce cost of the optics by limiting the number of lenses with aspherics or aspherodiffractive surfaces or by using faster manufactoring tools but it still remains the constraint of the cost per kg of Germanium and the fact that Germanium is not a moldable material.
In Infrared some Chalchogenide Glass are known to be transparent and moldable and at least two of them (AMTIR and GASIR) have been developed and commercialized with technical characteristics enabling
them to be used widely in IR equipmentis .
Concerning the price as they are made of Ge As Se or Ge Sb Se with a percentage not exceeding 33% Ge and as their density is lower than Ge it allows to get blanks typically half price per volume.
To get molded lenses specific process had to be developed to maintain the homogeneity of the material during the annealing , to achieve the right shape and roughness of the surface .In addition to that the
molded surface should not be polluted to allow further efficient coatings (anti-refection or Diamond Like ) to be deposited .
Nevertheless a minimum quantity of lenses is required to amortize the cost of the molding tools.