Silicon (Si)


Silicon (Si)

Silicon has blue-gray appearance. It has peak transmission range of 3 - 5 µm over the total transmission range of 1.2 - 8 µm. Due to high thermal conductivity and low density, it is suitable for laser mirrors and optical filters. Large blocks of silicon with polished surfaces are also employed as neutron targets in physics experiments. Si is low-cost and lightweight material, it is less dense than Ge or ZnSe & has a similar density to optical glass, so it can be used in some circumstances where weight is a concern. AR coating is recommended for most applications. Silicon is grown by Czochralski pulling techniques (CZ) and contains some oxygen which causes a strong absorption band at 9 µm, so it is not suitable for use with CO2 laser transmission applications. To avoid this, Silicon can be prepared by a Float-Zone (FZ) process.

Material Properties

Refractive Index

3.423 @ 4.58 µm

Abbe Number (Vd)

Not Defined

Thermal Expansion Coefficient (CTE)

2.6 x 10-6/ at 20℃



Transmission Regions & Applications

Optimum Transmission Range Ideal Applications
1.2 - 8 μm
3 - 5 μm AR coating available
IR spectroscopy, MWIR laser systems, MWIR detection systems, THz imaging
Widely used in biomedical, security and military applications


The right graph is transmission curve of 10 mm thick, uncoated Si substrate


For more in-depth specification data, please view our catalog optics to see our complete selection of optics made from silicon.