Germanium Ge Optical Window
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Germanium Ge single crystal is a chemically inert material with a transmission spectrum range of 2-14μm. It is a commonly used infrared optical material. It has the characteristics of high hardness, good thermal conductivity, and insoluble in water. Germanium single crystal has good mechanical properties and thermal conductivity, and is widely used in windows and optical components thermal imaging systems.
- Germanium glass is used on the windows of infrared thermal imagers and infrared thermometers.
- The main consideration is that the transmittance of germanium glass is only 40-50% without coating in the 8-14um band, while the transmittance can reach 90% after coating with anti-reflection film. In addition, most customers will also require DLC diamond-like carbon film to be coated on germanium glass to enhance the hardness of germanium glass and play a certain explosion-proof effect.
- Germanium has very little absorption at 10.6μm. Windows processed with germanium single crystals are the first choice for CO2 lasers and can also be used to make substrates for various filters. When the pressure is higher than 120KPa, germanium single crystals will form another allotrope, so the working pressure of germanium single crystals cannot exceed 120KPa (0.12MPa).
- Germanium is grown using the Cz method by a handful of manufacturers in Belgium, the United States, China, and Russia. Germanium’s refractive index changes rapidly with temperature, and at all wavelengths slightly above 350°K the material becomes opaque due to the band gap filling with hot electrons.
Technical parameters
| Items | Parameters |
|---|---|
| Material | Germanium (Ge) |
| Processable shapes | Circles, rectangles, polygons and other shapes |
| Diameter | 3mm-500mm ± 0.1mm |
| Center thickness tolerance | ± 0.05mm (we can process to ± 0.01mm with high precision) |
| Center deviation | 3′(we can process to 30 ″with high precision) |
| Surface accuracy | Reflection PV is better than 1/4λ, transmission PV is better than 1/10λ |
| Surface quality | 10-5 20-10 40-20 60-40 |
| Effective caliber | ≥90% |
| Coating | According to the custom requirements |
Germanium Ge Spectral Curve (coating before)
Physical and Chemical Properties of Germanium Ge
| Density (g/cm3) | 5.33 |
|---|---|
| Melting point (℃) | 936 |
| Dielectric Constant Static/High Frame | 16.6@9.37GHz（300K） |
| Thermal expansion coefficient (1/℃) | 6.1*10^-6@298K |
| Bulk modulus (GPa) | 77.2 |
| Shear modulus (GPa) | 67 |
| Thermal conductivity | 58.61@293K |
| Heat capacity (J/k.m.s) | 0.31 |
| Knoop hardness (kg/mm²) | 780 |
| Young's modulus(GPa) | 102.7 |
| Poisson's ratio | 0.28 |
| Elastic modulus | C11=129 C11=48.3 C11=67.1 |
Optical Properties of Germanium Ge
| Transmission wavelength range | 2000nm-12000nm |
|---|---|
| Absorption coefficient (1/cm) | 1.3*10^-3@3800nm |
| 3*10^-2@10600nm | |
| Thermo-optic coefficient, dn/dT (1/K) | 4.08*10^-4@10600nm |
Variation of Germanium Ge Refractive Index with Wavelength
| Wavelength (nm) | Refractive index (n) | Wavelength (nm) | Refractive index (n) |
|---|---|---|---|
| 2200 | 4.0879 | 8000 | 4.0057 |
| 3000 | 4.0451 | 9000 | 4.0040 |
| 3800 | 4.0267 | 10600 | 4.0028 |
| 5000 | 4.0160 | 11000 | 4.0025 |
| 6000 | 4.0107 | 12000 | 4.0021 |
| 7000 | 4.0079 | 13000 | 4.0018 |
Window Materials Quick Guide
| Wavelength range | Window material |
|---|---|
| 180 nm - 8.0 μm | Calcium Fluoride CaF2 |
| 185 nm - 2.1 μm | UV Fused Silica |
| 200 nm - 5.0 μm | Sapphire |
| 200 nm - 6.0 μm | Magnesium fluoride MgF2 |
| 600 nm - 16 µm | Zinc Selenide ZnSe |
| 1.9 - 16 μm | Germanium single crystal Ge |
| 2 - 5 μm | Barium fluoride BaF2 |
We can customize the optical window according to customer requirements or drawings.
For details, please consult:
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