Silicon – Si

lenses, windows, mirrors, filters and prisms



Silicon is primarily used in optical windows in the 3-5 micron region and as a substrate for optical filters. Silicon has low density and high thermal conductivity making it an ideal material to be used for laser mirrors. Grown by two different techniques, Czochralski (CZ) which contains some oxygen which causes an absorption band. Optical quality Silicon is normally lighted doped (5 to 40 ohm cm) and because it has a high refractive index it must be anti-reflection coated in order to achieve a high optical transmission.

Transmission Range 1.2 – 15.0 µ
Crystal Structure Diamond
Cleavage Plane 111
Colour Metallic lustre
Density 2.329 (25°)
Melting Point (°) 1420
Reflection Loss 46.1% (10µ) for 2 surfaces
Solubility index insoluble
Hardness (Knoop) 1150
Thermal Conductivity (cal/cm sec°C) 0.39 (40°C)
Thermal Expansion coefficient (/°C) 4.15×10-6(10-50°C)


Silicon (SI) windows and Silicon (SI) lenses

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