Windows for UV & VIS  Windows for IR

  G : Germanium (Click here to see the transmission spectrum)
  Z : Zinc Selenide (Click here to see the transmission spectrum)
  A : Gallium Arsenide (Click here to see the transmission spectrum)
  S : Silicon (Click here to see the transmission spectrum)

Germanium(Ge) Germanium is the most widely used substrate material for low and medium power infrared light sources.For typical thicknesses of a few millimetersit has less than 1% absorption between 2 and 15 microns, as long as the temperature is kept below 50oC. At higher temperatures the absorption increases rapidly.

the slight amount of power that is absorbed from medium intensity lasers is easilydissipated, due to a good thermal conductivity. However, in high power applications, the absorption coefficient increases as the substrate is heated by the laser, causing a condition known as thermal runaway, which ultimately can lead to failure. Environmental problems have little effect on germanium because it is inert, mechanically rugged and fairly hard.

Zinc Selenide(ZnSe) Zinc Selenide when chemically vapor deposited shows an extremely low coefficient of absorption compared with other infrared materials. This fact makes it very suitable for transmission optics with both pulsed and continuous wave high power lasers. The laser damage threshold is considerably higher than for germanium. The disadvantage however is that zinc selenide is relatively soft and scratches easily, and it is expensive.

Gallium Arsenide(GaSe) Gallium arsenide is a fairly new material to be used for infrared substrates. It is available to be used in sizes up to 4" in diameter. It has lower absorption than germanium which makes it a substrate material suitable for high power infrared lasers. Aloso ti does not show the thermal problems thatgermanium gives. In addition, it is virtually flat from 2 - 12 microns.

Silicon(Si)  Silicon is commonly used as substrate material for infrared reflectors and windows in the 1.5 - 8 micron region. The advantages are low cost and light weight weight, compared with other infraredsubstrate materials. unfortunately, it has severalabsorption bands beyon 8 microns. Therefore it is only used as a window in the spectral region when the substrates are thin and when low intensity IR sources sre used. Its hardness and durability, combined with a good thermal conductivity and a low coefficient of thermal ecpansion, makes silicon very suitable for use as high reflecting mirror substrates for IR lasers.