Si
Silicon is the most abundant element making up the Earth's crust, synthetic mono-crystalline silicon is the base for the modern electronics industry, and perhaps the most affordable infrared material. Silicon is commonly used as an optical window primarily in the 3-5μm band, and also could be used for 6-15μm transmission. The thickness is a very critical parameter of silicon optics. Silicon is often employed as a substrate for laser mirrors because of its high thermal conductivity and low density.
Silicon is commonly grown by CZ method and contains some oxygen which causes strong absorption band at 9μm and limits its transmission applications in 8-12μm.
Optical Properties
Bulk Absorption Coefficient <0.01/ cm @ 3μm
Refractive Index 3.4223 @ 5μm 3.4289 @ 4μm
Temperature change of Refractive Index 160×10-6/K
Thermal Properties
Thermal Conductivity at 25°C 160 W/m/K
Specific Heat 703 J/Kg/K
Thermal Expansion 2.6×10-6/K at 20?
Mechanical Properties
Young’s Modulus 131 GPa
Rupture Modulus 125 MPa
Shear Modulus 79.9 GPa
Knoop Hardness 1150
Poisson Ratio 0.266
Density 2.33 g/cm³
Typical Specification
Dimensional Tolerance +0.0/-0.1mm
Thickness Tolerance ±0.2mm
Center Thickness Tol. ±0.2mm
Surface Quality 10/5
Centering 3-5 arc minutes
Surface Accuracy 1/10 λ @ 10.6μm
Parallelism < 1 arc minute
Clear Aperture 90%