Silicon is commonly used as substrate material for infrared reflectors and windows in the 1.5 - 8 micron region. The strong absorption band at 9 microns makes it unsuitable for CO2 laser transmission applications, but it is frequently used for laser mirrors because of its high thermal conductivity and low density. Silicon is also useful as a transmitter in the 20 micron range.
Two different methods of ingot production are used to obtain a high quality monocrystalline Si substrate material: the Czochralski (Cz) crystal pulling technique, where a seeded crystal is pulled from the melt in a silica crucible and permitted to grow in a mechanically unconstrained environment, permitting precise control of the crystal orientation and shape (standard grade), and the Float Zone (Fz) refining technique (premium hyperpure grade), where a seeded molten zone is supported by surface tension between two vertical cylindrical rods of the material and passed through a heated crucible, re-orientating and refining the crystal through its travel. The most noticeable optical difference between the two grades is the presence of a significantly more pronounced absorption band at approximately 9µm (1110 cm-1) in Cz material, and a reduced absorption profile in premium hyperpure grade (Fz) material beyond 20µm, following the multi-phonon absorption region, where the material exhibits a nearly complete transparency recovery.

Safetyrich optical selected high quality material to satisfy with customer different request.

	Transmittance Property (Reference Data)

Refractive Index
Wevelength (µm)	n	Wevelength (µm)	n
1.40	3.49	2.05	3.45
1.50	3.48	2.50	3.44
1.66	3.47	3.5-5.0	3.43
1.82	3.46	6.0-25	3.42

Optical property
Crystal Class	Cubic
Density at 293k ,g/cm3	2.329
Thermal Conductivity  W/(mk) at 125K at 313K at 400K	598.6 163 105.1
Thermal Expansion 1K at 75K at 293K at 1400K	-0.5x10-6 2.6x10-6 4.6x10-6
Lattice Constant,Å	5.43
Molecular Weight	29.09
Dielectric Constant for 9.37x109Hz	13
Melting Point,K	1690
Specific Heat,cal/(gK) at 298K at 1800 K	0.18 0.253
Debye Temperature,K	640
Knoop Hardness,kg/mm2	1100
Young's Modulus,GPa	130.91
Shear Modulus,Gpa	79.92
Bluk Modulus,GPa	101.97
Poisson's Ratio	0.28
Mohs Hardness	7
Bandgap,eV	1.1
Water Solubility	None