Germanium (Ge)

Germanium is a high index material that is used to manufacture Attenuated Total Reflection (ATR) prisms for spectroscopy. Its refractive index is such that Germanium makes an effective natural 50% beamsplitter without the need for coatings. Germanium is also used extensively as a substrate for production of optical filters. Germanium covers the whole of the 8-14 micron thermal band and is used in lens systems for thermal imaging. Germanium can be AR coated with Diamond producing an extremely tough front optic.

Transmission Range : 1.8 to 23 µm (1)
Refractive Index : 4.0026 at 11 µm (1)(2)
Reflection Loss : 53% at 11 µm (Two surfaces)
Absorption Coefficient : <0.027 cm-1 @ 10.6 µm
Reststrahlen Peak : n/a
dn/dT : 396 x 10-6 /°C (2)(6)
dn/dµ = 0 : Almost constant
Density : 5.33 g/cc
Melting Point : 936 °C (3)
Thermal Conductivity : 58.61 W m-1 K-1 at 293K (6)
Thermal Expansion : 6.1 x 10-6/°C at 298K (3)(4)(6)
Hardness : Knoop 780
Specific Heat Capacity : 310 J Kg-1 K-1 (3)
Dielectric Constant : 16.6 at 9.37 GHz at 300K
Youngs Modulus (E) : 102.7 GPa (4) (5)
Shear Modulus (G) : 67 GPa (4) (5)
Bulk Modulus (K) : 77.2 GPa (4)
Elastic Coefficients : C11=129; C12=48.3; C44=67.1 (5)
Apparent Elastic Limit : 89.6 MPa (13000 psi)
Poisson Ratio : 0.28 (4) (5)
Solubility : Insoluble in water
Molecular Weight : 72.59
Class/Structure : Cubic Diamond, Fd3m

• Its high index is desirable for the design of lenses that might not otherwise be possible.
• It has nearly the highest density of the IR-transmitting materials, a consideration when designing for weight restricted systems.
• It is subject to thermal runaway; the hotter it gets, the more the absorption increases. Pronounced transmission degradation starts at about 100°C and begins rapidly degrading between 200°C and 300°C, resulting in possible catastrophic failure of the optic.
• Ge is generally less expensive than ZnSe and Cleartran.
• Ge is diamond turnable.

Typeical application: Thermal imaging, FLIR.

Products manufactured: Lenses, Aspheric Lenses, Binary (Diffractive) Lenses, Windows, Optical Beamsplitters, Optical Filters, Wedges.

Surface Finish: Typical 40-20 or 60-40 scratch-dig. Diamond Turned 120 Angstroms rms or better.
Surface Flatness: Range from 1/2 wave to 2 waves @633nm depending on the system performance requirements.
AR coating: BBAR for 3 to 5µm, 8 to 12µm, and the 3 to 12µm spectral regions. Other specialized bands are possible from 2 to 12 µm.

Zinc Selenide (ZnSe)

ZnSe is used widely for IR components, windows and lenses, and for spectroscopic ATR prisms. Zinc Selenide is one of the materials of choice for CO2 laser optics operating at 10.6 microns.

Transmission Range : 0.6 to 21.0 µm
Refractive Index : 2.4028 at 10.6 µm
Reflection Loss : 29.1% at 10.6 µm (2 surfaces)
Absorption Coefficient : 0.0005 cm-1 at 10.6 µm
Reststrahlen Peak : 45.7 µm
dn/dT : +61 x 10-6/°C at 10.6 µm at 298K
dn/dµ = 0 : 5.5 µm
Density : 5.27 g/cc
Melting Point : 1525°C (see notes below)
Thermal Conductivity : 18 W m-1 K-1 at 298K
Thermal Expansion : 7.1 x 10-6 /°C at 273K
Hardness : Knoop 120 with 50g indenter
Specific Heat Capacity : 339 J Kg-1 K-1
Youngs Modulus (E) : 67.2 GPa
Bulk Modulus (K) : 40 GPa
Apparent Elastic Limit : 55.1 MPa (8000 psi)
Poisson Ratio : 0.28
Solubility : 0.001g/100g water
Molecular Weight : 144.33
Class/Structure : HIP polycrystalline cubic, ZnS, F43m

Typeical application: Thermal imaging, FLIR.

Products manufactured: Lenses, Aspheric Lenses, Binary (diffractive) Lenses, Windows, Optical Beamsplitters and Optical Filters, Prism.

Surface Finish: Typical 40-20 or 60-40 scratch-dig. Diamond Turned 150 Angstroms rms or better.
SurfaceFlatness: Range from 1/2 wave to 2 waves @633nm depending on the system performance requirements.
AR coating: BBAR for 0.8 to 2.5µm, 3 to 5µm, 1 to 5µm, 8 to 12µm, and the 3 to 12µm spectral regions and single wavelength coating AR at 10.6µm. Many other specialized wavelength bands are possible within the 0.6 to 16µm range.

Product Notes:
Zinc Selenide is produced by synthesis from Zinc vapour and H2Se gas, forming as sheets on Graphite susceptors. Zinc Selenide is microcrystalline in structure, the grain size being controlled to produce maximum strength. Single crystal ZnSe is available, but is not common but has been reported as having lower absorption and thus more effective for CO2 optics.

Zinc Selenide oxidizes significantly at 300°C, exhibits plastic deformation at about 500°C and dissociates about 700°C. For safety, Zinc Selenide windows should not be used above 250°C in normal atmosphere.

Zinc Sulphide Multispectral (ZnS)

ZnS Multispectral (water-clear) is used for IR windows and lenses in the thermal band (8 to 14 µm) where maximum transmission and lowest absorption is required. Also selected for use where visible alignment is an advantage.

Transmission Range : 0.37 to 13.5 µm
Refractive Index : 2.20084 at 10 µm
Reflection Loss : 24.7% at 10 µm (2 surfaces)
Absorption Coefficient : 0.0006 cm-1 at 3.8 µm
Reststrahlen Peak : 30.5 µm
dn/dT : +38.7 x 10-6 /°C at 3.39 µm
Density : 4.09 g/cc
Melting Point : 1827°C
Thermal Conductivity : 27.2 W m-1 K-1 at 298K
Thermal Expansion : 6.5 x 10-6 /°C at 273K
Hardness : Knoop 160 with 50g indenter
Specific Heat Capacity : 515 J Kg-1 K-1
Dielectric Constant : 88
Youngs Modulus (E) : 74.5 GPa
Apparent Elastic Limit : 68.9 MPa (10,000 psi)
Poisson Ratio : 0.28
Solubility : 65 x 10-6 g/100g water
Molecular Weight : 97.43
Class/Structure : HIP polycrystalline cubic, ZnS, F42m

Due to its good transmission in the VIS and IR, Cleartran is an ideal choice for systems with a visible cameras,and and various IR detectors or IR cameras.

Typeical application: Visible imaging, thermal imaging, FLIR, astronomy

Products manufactured: Lenses,aspheric lenses ,binary(diffractive) lenses,windows,beamsplitters and optical filters and prisms

Surface Finish: Typical 40-20 or 60-40 scratch-dig. Diamond Turned 100 Angstroms rms or better.
Surface Flatness: Range from 1/2 wave to 2 waves @633nm depending on the system performance requirements.
AR coating: BBAR for 0.8 to 2.5µm, 3 to 5µm, 1 to 5µm, 8 to 12µm, and the 3 to 12µm spectral regions. Other specialized bands are possible from 0.4 to 12 µm.

Product Notes:
Zinc Sulphide oxidizes significantly at 300°C, exhibits plastic deformation at about 500°C and dissociates about 700°C. For safety, Zinc Sulphide windows should not be used above 250°C in normal atmosphere.

Silicon (Si)

Silicon is used as an optical window primarily in the 3 to 5 micron band and as a substrate for production of optical filters. Large blocks of Silicon with polished faces are also employed as neutron targets in Physics experiments.

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

With one of the lowest densities of the common IR materials, it is ideal for systems with weight constraints.
It is harder than Ge and not as brittle.
It is the lowest material cost option of all the IR materials.
Silicon is diamond turnable.

Typeical application: Thermal imaging, FLIR.

Products manufactured:Lenses, Aspheric Lenses, Binary(Diffractive) Lenses, Windows, Optical Beamsplitters, Optical Filters, Wedges.

Surface Finish: Typical 40-20 or 60-40 scratch-dig. Diamond Turned 120 Angstroms rms or better.
Surface Flatness: Range from 1/2 wave to 2 waves @633nm depending on the system performance requirements.

Product Notes:
Silicon is grown by Czochralski pulling techniques (CZ) and contains some oxygen which causes an absorption band at 9 microns. To avoid this, Silicon can be prepared by a Float-Zone (FZ) process. Optical Silicon is generally lightly doped ( 5 to 40 ohm cm) for best transmission above 10 microns. Silicon has a further pass band 30 to 100 microns which is effective only in very high resistivity uncompensated material. Doping is usually Boron (p-type) and Phosphorus (n-type)..

Gallium Arsenide (GaAs)

Gallium Arsenide has specialist applications in far IR optics and lens systems.

Transmission Range : 1 to 16 µm (1)
Refractive Index : 3.2727 @ 10.33 µm (1)
Reflection Loss : 44% @ 10.33 µm
Absorption Coefficient : 0.01 cm-1
Reststrahlen Peak : n/a
dn/dT : 147 x 10-6/°C @ 10 µm (4)
dn/dµ = 0 : 6.3 µm
Density : 5.315 g/cc
Melting Point : 1511°C
Thermal Conductivity : 48 W m-1 K-1 @ 273K (2)
Thermal Expansion : 5.7 x 10-6 /°C at 300K (3)
Hardness : Knoop 750
Specific Heat Capacity : 360 J Kg-1 K-1
Dielectric Constant : 12.91 at low frequencies
Youngs Modulus (E) : 84.8 GPa
Bulk Modulus (K) : 75.5 GPa
Apparent Elastic Limit : 71.9 MPa
Poisson Ratio : 0.31
Solubility : Insoluble in water
Molecular Weight : 144.64
Class/Structure : Cubic ZnS, F43m, (100) cleavage

• It is nearly as hard ,strong and dense as Ge.
• It is commmonly used in applications where toughness and durability are of great importance.
• It has a low absorption coefficient of 0.01 cm-1 from 2.5 to 12 um
• Its optical -grade material is generally more expensive than Ge and ZnSe.
• GaAs is diamond turnable.

Typeical application: Thermal imaging, CO2 laser systems, FLIR.

Products manufactured: Lenses, Aspheric Lenses, Windows, Wedges.

Surface finish: Typical 40-20, 60-40 80-50 or 120-80 scratch-dig depending upon system performance requirements.

Surface Flatness: Ranges from 1/2 wave to 2 waves @633nm depending on the system performance requirements.

AR coating options: BBAR for 3 to 5µm or 8 to 12µm spectral region. Many other specialized bands are possible within the 2 to 15µm spectral region.

OptocCity offer Windows, Prisms, Wedges, Lenses, and other optical components according to customer's specifications and drawings.