Germanium Glass – used to see heat
Germanium glass is typically used for solutions in thermal systems, where you want to be able to make accurate infrared image measurements without the measuring devices being disturbed by UV and VIS light. Germanium glass is what is called a high-density IR-transmitting material that blocks UV and VIS wavelengths. Germanium lets light in the wavelengths between 8000-14000 nanometers (the infrared spectrum) pass through and basically blocks all other light.
The specialized germanium glass is typically used in technical imaging solutions that can visualize heat differences. For example, in food production, where you can use infrared cameras to see if a meatball is cooked through. By using germanium, extraneous light is sorted out and thus the infrared images become unambiguous.
Infrared lasers are also a field where germanium glass is used. Infrared lasers best from the military, who use it for targeting. However, infrared lasers are also used for many civilian purposes in both medicine and industry.
An additional plus of germanium glass is that it is unaffected by alkalis and acids with the exception of nitric acid.
Ironically, Germanium’s Achilles heel is heat. If the glass gets too hot it blocks all light completely. Typically it gradually starts shutting off from light at 50 degrees Celsius and typically it shuts off completely at 100 degrees Celsius. At higher temperatures, you can use zinc selenium glasses, which are taken home to order.
Germanium is generally expected to operate at room temperature. Therefore, all tolerances are given as standard at 293 K (293 degrees Celsius = 19.85 degrees Celsius).
Germanium – being a very specialized glass – is taken home on order only.