Germanium Windows 

In applications demanding robust optics, Germanium Windows prove to be invaluable. Functioning as optical windows with UV and visible light opacity and an extensive transmission range in the infrared (IR) spectrum, these windows exhibit minimal chromatic aberration thanks to low dispersion. To enhance performance, we recommend the application of an anti-reflection coating due to the high index of refraction (4.0 from 2-14μm).

Germanium windows
Germanium Windows

Broad Transmission Range in Infrared (IR) Spectrum: Germanium windows boast unparalleled transparency to infrared wavelengths, spanning from 2 µm to 14 µm. This unique characteristic makes them suitable for IR laser applications, facilitating the efficient passage of IR radiation while maintaining opacity to UV and visible light. The broad transmission range also makes them ideal for various IR applications, including thermal imaging.

Minimal Chromatic Aberration and Low Dispersion: Germanium windows exhibit low dispersion, resulting in minimal chromatic aberration. This ensures superior image quality and reduced color distortion, making them ideal for applications that necessitate precise optical performance, such as weight-sensitive systems requiring accurate imaging.

High Index of Refraction and Anti-Reflection Coating: With a high index of refraction measuring 4.0 from 2 – 14 µm, germanium is an excellent candidate for anti-reflection coatings. These coatings optimize light transmission by reducing undesirable reflections that could compromise optical system efficiency. Anti-reflection coatings like BBAR (Broadband Anti-Reflection) coatings enhance germanium optical windows’ performance, ensuring maximum transmission properties.

Robustness and Durability in Harsh Environments: Germanium (Ge) possesses notable physical properties, characterized by its heavy and hard composition, boasting a Knoop Hardness of 780—nearly double that of MgF. With a density of 5.33 g/cm3, it becomes a favored choice for applications prioritizing durability. However, caution is advised for applications with routine temperatures exceeding 100°C, as germanium’s transmission properties experience a sharp decline with increasing temperature, a phenomenon known as thermal runaway. Despite its sensitivity to temperature, germanium excels in IR laser applications, particularly in scenarios necessitating resilient optics. Additionally, it serves as an effective long pass filter, transmitting only wavelengths greater than 2 µm. Germanium is nonreactive to air, water, alkalis, and many acids, displaying high scratch resistance.

Germanium Window Specifications for Optimized Performance

Size and Coating Options: Germanium Windows are available in sizes ranging from 2 mm to 100 mm in diameter, catering to a wide range of applications, including thermal imaging and IR laser systems. Customers can select from two coating options: 2-14 µm or 8-12 µm (BBAR coating or DLC/BBAR) coatings, designed to cater to specific application requirements.

Precision Flatness and Parallelism: At Avantier, strict quality standards ensure the factory standard for flatness is maintained at 1/2 lambda. This guarantees minimal deviations from an ideal flat surface, enhancing overall optical performance and minimizing image distortion. Additionally, Avantier’s germanium windows exhibit a deviation in parallelism below 3 arc minutes, ensuring optimal alignment of the two optical surfaces and reducing light degradation.

Surface Finish and Transmission Rate: Avantier maintains exceptional surface finish quality with a rating of 20-10 and no digs, ensuring unparalleled optical clarity. Moreover, the germanium windows exhibit an impressive transmission rate of >47.5% @ 3.7-4.8 µm, guaranteeing efficient IR radiation transmission and optimizing the performance of the optical system in thermal imaging applications.

Applications of Germanium Windows in IR and Optical Systems: The versatility of germanium windows enables their deployment across various industries, showcasing their prowess in specific applications:

  • IR Laser Systems: Germanium windows are extensively utilized in IR laser applications, capitalizing on their high transmission range and durability to ensure reliable and efficient laser performance, especially in weight-sensitive systems that require compact and powerful laser systems.
  • Long Pass Filters: By transmitting only wavelengths greater than 2 µm, germanium windows effectively serve as long pass filters, facilitating selective passage of specific IR wavelengths. This feature is particularly useful in IR applications and thermal imaging systems.
  • Rugged Environments: In environments characterized by extreme temperatures and harsh conditions, germanium windows excel by withstanding thermal stress and offering unmatched robustness. Their durability makes them ideal for weight-sensitive systems that need optics capable of enduring challenging environments without compromising performance.

Handling, Cleaning, and Storage of Germanium Windows for Longevity:

  • Hazards of Germanium Dust: Handling germanium optics necessitates caution, as germanium dust can be hazardous. It is imperative to follow meticulous handling practices, such as wearing gloves and washing hands after contact, to minimize exposure. This is especially important when dealing with optical components for weight-sensitive systems, where the presence of dust or debris can impact precision.
  • Recommended Cleaning Methods: For cleaning germanium lenses, reagent-grade acetone, ethanol, isopropyl alcohol, or methanol, along with lint-free germanium lens wipes, are suitable options. However, caution must be exercised when using nitric acid, as it may corrode neighboring optics or mounts. Proper cleaning is crucial for maintaining optimal performance in IR applications and thermal imaging systems.
  • Alternative Cleaning Technique: Liquid CO2 cleaning, employing specialized nozzles, offers a precise and controlled cleaning method, effectively removing stubborn compounds and thin films from germanium windows. This alternative cleaning technique is particularly useful in weight-sensitive systems, where even minor contaminants can impact performance.
  • Storage of Germanium Windows: Proper storage conditions are pivotal in maintaining optimal performance and extending the operational lifespan of germanium windows. We recommend storing these windows between 15 and 25°C, with humidity controlled below 30%. By following appropriate storage procedures, the longevity and reliability of germanium windows in weight-sensitive systems and thermal imaging applications can be ensured.
Germanium windows
Germanium windows

Germanium windows

Factory Standard – Germanium  Window 

with different sizes (2 mm – 100 mm)


+0/-0.05 mm


+0.01/-0.03 mm


1/2 Lambda


< 3 arc min

Polished surface finish

20-10 (no dig)


protective bevel

Transmission rate

>47.5%@3.7-4.8um or according to customer’s specifications

Avantier Customization Options

Avantier offers a wide range of germanium windows, accompanied by customization options tailored to your specific needs. Experience unparalleled optical performance for your rugged applications with Avantier’s germanium windows. Contact us now to explore our exceptional range of products.

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