Alfa Chemistry customizes infrared optics using germanium (Ge), crystalline material with the highest refractive index of any commonly used infrared material. Due to its high refractive index, it can function as a 50% natural beam splitter between 2 and 14 µm. Its comparatively high density and hardness make it the perfect substrate for optical systems used in infrared optics. All custom AMTIR optics are rigorously tested by skilled experts at cutting-edge metrology facilities, giving customers the peace of mind that their needs will be met. Contact us for your customer service as soon as possible!
Our Services
Alfa Chemistry can produce high-quality customized germanium parts to your exact specifications, including but not limited to windows, lenses, aspheric mirrors, and prisms. Diamond-like carbon (DLC) coatings and broadband-enhanced transmission (BBAR) coatings are two examples of the coated and uncoated choices we may offer. Our average manufacturing needs are listed in the table below. If your needs are not covered by the aforementioned list, get in touch with our technical sales team. We can help you since we have a lot of experience in this area.
Ge Windows
The most commonly requested specifications for an Ge window are as follows:
| Diameter Range | 5 mm ~ 300 mm |
| Diameter Tolerance | ± 0.1 mm |
| Centre Thickness | up to 50 mm |
| Centre Thickness Tolerance | ± 0.05 mm |
| Clear Aperture | 90% |
| Centration Tolerance | 1 arc minute |
| Form Error | better than 0.5 wave (633 nm) over aperture |
| Surface Radius Tolerance | 1 fringe over aperture |
| Linear Dimension | up to 300 mm |
| Linear Tolerance | ± 0.1 mm |
| Angular Tolerance | 5 arc minutes |
| Edge Finish | ground, blacked |
| Chamfer | 0.3x0.3@45° |
| Surface Quality | 40-20 scratch/ dig |
| Coatings | BBAR coating@1-14μm; Diamond-Like carbon (DLC) coating@1-14μm |
Ge Prisms
The most commonly requested specifications for an Ge prism are as follows:
| Length of Hypotenuse | up-to 150 ± 0.1 mm |
| Length of Sides | up-to 150 ± 0.1 mm |
| Thickness | 100 ± 0.05 mm |
| Angle Tolerance | better than 1 arc minute |
| Edge Finish | ground, blacked |
| Clear Aperture | 90% of entrance dimensions |
| Chamfer | 0.3x0.3@45° |
| Form Error | 0.2 fringe from test flat |
| Surface Quality | 20-10 scratch/dig |
Ge Ground Blanks
The most common specifications for Ge ground blanks are as follows.
| Diameter Range | less than 5 mm to 300 mm |
| Diameter Tolerance | better than ± 0.5 mm |
| Centre Thickness | up to 50 mm |
| Centre Thickness Tolerance | better than ± 0.5 mm |
| Clear Aperture | 90% |
| Linear Dimension | up to 300 mm |
| Linear Tolerance | better than ± 0.5 mm |
| Angular Tolerance | better than 10 arc minutes |
| Edge Finish | fine ground N6 |
| Chamfer | 0.3x0.3@45° |
Applications:
- FLIR and Thermal Imaging: Ge is the perfect material for use in thermal imaging systems, both as a protective window and/or lens within the system because it transmits in the MWIR and LWIR bands.
- Low Power CO2 Lasers: Ge transmits at 10.6 µm, therefore it can be used in CO2 laser systems. However, it cannot survive higher power lasers, which are more frequently employed with zinc selenide.
- Pyrometer: Ge is frequently employed as a protective window in pyrometers because of its durability, particularly when a DLC coating has been added to the exposed surface.
Ge's Optical Properties
Ge, a material with a high refractive index that by nature absorbs UV and visible light, is frequently employed as a substrate for infrared long pass filters. Due to Ge's inherently high reflectivity, a transmission-enhancing layer is frequently used to raise the transmittance to over 85%. DLC coatings can be used to improve the durability and transmission of exposed surfaces.
Fig 1. Optical transmission range of germanium sulphide glass by CVD. (Huang K, et al. 2004)
If the optical system is weight-sensitive, it must take into account Ge's high density. If weight is a problem, silicon might be a preferable choice because it has a density that is almost half that of germanium. Thermal runaway is another danger. Ge loses transmittance as the temperature rises due to an increase in absorption; at 100 °C, it is virtually opaque, and at 200 °C, it is completely opaque. To lessen the chance of optical failure, it should be utilized in systems running at temperatures below 100°C.
Below is a quick description of Ge's optical characteristics. For more information on the properties of Ge materials please click here.
| Transmission Range | 0.75 to 14.0 µm |
| Refractive Index | 2.4981@10 µm |
| Melting Point | > 360 ℃ |
| Density | 4.4 g/cm3 |
| Hardness | 170 |
If you need technical advice, please contact our technical team to learn more about our high-quality services.
Reference
- Huang H, et al. (2004). "Deposition and Characterization of Germanium Sulphide Glass Planar Waveguides." Optics Express. 12(11): 2501-2506.