Discover the optical properties and applications of Germanium IR windows. Learn how this high-density material efficiently transmits infrared light.
Germanium (Ge) is a robust, high-density material with excellent infrared (IR) transmission properties, effectively blocking ultraviolet (UV) and visible (VIS) light while permitting IR wavelengths from 2µm. With the highest refractive index among common IR transmitters and minimal optical dispersion, Germanium is a prime choice for advanced lens designs that require these specific optical characteristics. Anti-reflective (AR) coating is advisable to enhance performance.
SHAPE OPTICS Germanium (Ge) Crystals Specifications
| Attribute | Details |
|---|---|
| Diameter (mm) | 12mm ~ 380mm |
| Length (mm) | Customized |
| Electrical Resistivity | 0.005Ω ~ 50Ω/cm |
| Crystal Structure | Single Crystal, PolyCrystal |
| Crystal Purity | 99.999% ~ 99.99999% |
| Conduction Type | N/P |
| Surface Roughness | Ramax 0.2µm to 4.0µm |
| Refractive Index at 10.6µm | 4.0052 |
| Absorptance at 10.6µm | ≤0.035 |
These specifications provide key details about the Germanium (Ge) crystals offered by SHAPE OPTICS.
Germanium IR windows efficiently transmits over 45% of IR light from 2-14μm up to temperatures of 45°C. However, its transmission capacity gradually decreases at 100°C and deteriorates more rapidly above 200°C. Due to this sensitivity to high temperatures, Germanium windows is not recommended for environments exceeding these heat thresholds, as exposure can result in significant material failure. Additionally, its high density may pose considerations in applications where weight is a constraint. The material’s hardness is rated at HK780, slightly above that of GaAs, with which it shares similar mechanical properties.
This material is predominantly used in thermal imaging as a front optic and is advantageous for producing wide-angle lenses and microscope components due to its refractive index. Germanium windows is also integral to Forward Looking Infrared (FLIR) and Fourier Transformed Infrared (FTIR) spectroscopy systems, among other analytical instruments.
Germanium IR windows Transmission Range
Germanium is highly transparent to infrared light. Its transmission range is from about 2 to 14 microns, which makes it extremely useful in mid-wave infrared (MWIR) and long-wave infrared (LWIR) systems. This broad transmission range is one of the key reasons it’s chosen for thermal imaging, military applications, and spectroscopy.
Transmission Curve of Ge Window without AR Coating
Optical Properties
- Refractive Index: Germanium has a high refractive index, around 4.0 at 10 microns, which is beneficial for designing systems with fewer lens elements.
- Dispersion: It has relatively low optical dispersion, which helps in reducing chromatic aberration in the design of optical systems.
Factory Standard
- Germanium Window with different sizes (2 mm – 100 mm)
- Diameter: +0/-0.05 mm
- Thickness: +0.01/-0.03 mm
- Flatness: 1/2 Lambda
- Parallelism: < 3 arc min
- Polished surface finish:20-10 (no dig)
- Bevel: protective bevel
- Transmission rate: >47.5%@3.7-4.8um or according to customer’s specifications
Contact us for manufacturing limit or custom specifications.
Physical Properties
- Density: Germanium is quite dense, about 5.323 g/cm³, which impacts the weight of the optical system.
- Hardness: It’s relatively hard, but not as hard as materials like diamond, making it moderately scratch-resistant but easier to work with in manufacturing.
Germanium IR windows Thermal Properties
- Thermal Conductivity: It has moderate thermal conductivity, which is important for applications where temperature changes are a factor.
- Thermal Expansion: Germanium has a thermal expansion coefficient of about 6 x 10^-6 K^-1, which needs to be considered in designs where the optic will be subjected to varying temperatures.
Sensitivity to Environment
- Hygroscopicity: Unlike materials like sodium chloride or potassium bromide, germanium is not hygroscopic, meaning it does not absorb water from the air and degrade.
- Durability: It is robust in harsh environments but is opaque in the visible spectrum, so it is not suitable for applications requiring visible light transmission.
Germanium IR windows Applications
Germanium is used in a variety of IR applications including:
- Thermal imaging systems
- Military and defense optics, such as night-vision systems
- Spectroscopic components in science and industry
- Satellite imaging systems
Limitations of Germanium IR windows
- Cost: Germanium is relatively expensive compared to other optical materials, which can affect the cost-efficiency of an optical design.
- Sensitivity to Temperature: High temperatures can affect its transmission properties, limiting its use in very high-temperature environments.
Given these properties, germanium windows and lenses are particularly suited to applications where robust, high-performing IR transmission is needed, though considerations around cost, weight, and thermal effects are necessary in the design phase.
At Shape Optics , we offer an array of Germanium Windows, DLC/AR coated for 7-12 µm. We also provide custom Germanium windows tailored to specific requirements. Our portfolio includes Germanium lenses, prisms, and blanks, crafted to meet diverse application needs. Each component undergoes rigorous testing by our expert technicians in our state-of-the-art metrology lab, ensuring compliance with our stringent quality standards.
