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Silicon (Si) Windows

  • Low density and light weight
  • Maximum diameter 300mm
  • Transmitting range 1.2μm to 7.0μm
  • Coating options: DLC coating, AR coating
  • Low cost
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Materials Silicon crystals Diameter Range ~ 300mm
Aperture >90% Dimension Tolerance +0.0/-0.2mm
Thickness Tolerance +/-0.1mm Surface Quality 60/40 S/D
Parallelism 1 arc minute Chamfer 0.3-0.5mmx45degree
Coating AR/AR or DLC/AR


Basic Properties:

Transmission Range 1.2 to 15 μm (1) Refractive Index 3.4223 @ 5 μm (1) (2)
Reflection Loss 46.2% at 5 μm (2 surfaces) Absorption Coefficient 0.01 cm-1 at 3 μm
Reststrahlen Peak n/a dn/dT 160 x 10-6 /°C (3)
dn/dμ = 0 10.4 μm Density 2.33 g/cc
Melting Point 1420 °C Thermal Conductivity 163.3 W m-1 K-1 at 273 K
Thermal Expansion 2.6 x 10-6 / at 20°C Hardness Knoop 1150
Specific Heat Capacity 703 J Kg-1 K-1 Dielectric Constant 13 at 10 GHz
Youngs Modulus (E) 131 GPa (4) Shear Modulus (G) 79.9 GPa (4)
Bulk Modulus (K) 102 GPa Elastic Coefficients C11=167; C12=65; C44=80 (4)
Apparent Elastic Limit 124.1MPa (18000 psi) Poisson Ratio 0.266 (4)
Solubility Insoluble in Water Molecular Weight 28.09
Class/Structure Cubic diamond, Fd3m

Silicon (Si) Windows manufactured from optical grade silicon are popular for the 1.2 - 7μm spectral region due to their low cost and low density. Due to its low density (half that of germanium or zinc Selenide), silicon is ideal for weight sensitive applications, especially those in the MWIR thermal imaging 3 - 5μm region. Density is 2.329 g/cm3 and Knoop Hardness is 1150, making it harder and less brittle than germanium.


1. Transmission curve of the Silicon windows (no coating)


2. Transmission curve of the Silicon windows with AR/AR coating at 3-5μm