| Materials | Optical grade germanium single crystals | Diameter Range | ~280mm |
| Thickness Tolerance | ±0.2mm (Optional: ±0.1mm or ±0.05mm) |
Surface Quality | 60/40 S/D |
| Fringes (N) | customized | Irregularity (delta N) | customized |
| Chamfer | 0.1~0.3mmx45degree | Coating(optional) | AR/AR@7-14μm DLC/AR@7-14μm BBAR/BBAR@3-12μm See the curves below |
Physical and Optical Properties:
| Transmission Range | 1.8 to 23μm (1) | Refractive Index | 4.0026 at 11μm (1)(2) |
| Reflection Loss | 53% at 11μm (2 surfaces) | Absorption Coefficient | <0.027 cm-1 @ 10.6μm |
| 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 |
Germanium domes are a special kind of window made of germanium crystal with a curved profile, Ge domes are excellent for IR applications due to their broad transmission range of 2-14μm, rejection to the visible spectrum and low chromatic dispersion, functioning as a protective barrier to shield sensitive components from hostile environments while let the portion of IR radiations of interest pass unhindered. Germanium domes are often used in IR thermal imaging cameras operating in the 2µm to 14µm spectral range, covering the LWIR (8-12μm) and MWIR (3-5μm) region. The rugged nature of Ge makes it competent at handling extreme environments (such as aerospace and defense). Germanium domes can be AR coated with Diamond (DLC coating or Hard carbon coating), producing a front optic with striking toughness.
Technical Images:
1. Transmission curve for Ge windows with coating AR/AR of 1mm thickness
