Si is a semiconductor material commonly used in infrared optical systems operating in the near-IR and MW spectral band. Silicon has the lowest density among common infrared materials, making it ideal for systems with weight constraint. Products such as windows, lenses, prisms, filters and wedges in different sizes are available.
Germanium has the highest index of refraction among commonly used infrared transmitting materials .It is a very popular material for systems operating in the 3-to5-or 8 to 12-μm spectral region. Germanium has nearly the highest density of the infrared transmitting material and this should be taken into account when designing for weight-restricted systems. Germanium is subject to thermal runaway, which means that the hotter it gets, the more the absorption increases. Products such as lenses, windows, beamsplitters, filters, wedges etc. are available.
Calcium Fluoride is used for optical windows, lenses and prisms in the 0.15 μm - 9 μm range. This material has found wide use in high power laser optics due to its low absorption. Polished surfaces are stable and will last several years under normal conditions. Due to its low refractive index, Calcium Fluoride can be used without anti-reflection coating.
Calcium fluoride is grown by vacuum Stockbroker technique. Material for IR use is grown using naturally mined fluorite, in large quantities at relatively low cost.
Magnesium Fluoride is used for optical elements in the infrared where extreme ruggedness and durability is required. Its useful transmission range is 0.11 μm - 7.5 μm. Irradiation does not lead to color centers. Magnesium fluoride is a rugged, hard material which is resistant to thermal and mechanical shock. Considerable mechanical shock is needed to cause cleavage which is near perfect when it occurs. The natural form of MgF2 is known as Sellaite. Magnesium fluoride is a positive birefringent crystal grown normally to 135 mm diameter by vacuum Stockbroker technique, seeding along the C-axis.
Zinc selenide, a chemically vapor deposited material, is used in high-power CO2 laser systems because of its low absorption at 10.6μm. It is also a popular choice in systems operating at various bands within its wide transmission range. Products such as lenses, windows, beamsplitters, filters, and prisms are available in different sizes.
Sapphire crystal is extremely hard and scratch resistant useful for the visible and IR spectrum. Optical sapphire is made to a random orientation or cut to a specified orientation. It has excellent thermal conductivity at low temperatures allowing single crystal sapphire to be used in many diverse fields requiring thermal conduction and heat radiation. Sapphire has high dielectric constant and is resistant to common chemical acids and alkaline. Optical sapphire has no colouration and with a selection of grades of sapphire transmission ranging from 170nm to 6 microns . Sapphire windows, lenses, prisms and domes in various shapes, sizes and forms i.e. squares, plates, rectangles and discs are available