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Custom Germanium Optics

Germanium IR Lenses

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All optical components 100% QA checked
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Knight Optical is at the forefront of providing top-tier germanium optics and infrared components tailored to your unique specifications. Our range encompasses germanium IR lenses and other optical elements such as germanium windows, germanium aspheric lenses, and germanium prisms.

We are able to provide our customers with large germanium optics with dimensions exceeding 230mm, ideal for aerospace applications.

Coatings are often critical to germanium’s performance and at Knight Optical we ensure we can provide a variety of coating types to suit your application, mainly antireflective (AR) and diamond-like carbon (DLC) coatings. Our AR/AR coatings, often essential for components being used within an optical system, exhibit high transmission wavebands above 87%, and our AR/DLC coating type is ideal for germanium optics being used in a rugged environment, where the DLC-coated surface can be exposed to harsh conditions including abrasives. Our stock germanium can be purchased with coatings extending over the MWIR and LWIR coating ranges including 3-8µm, 3-12µm, and 7-14µm.

Our typical manufacturing specifications are listed below, however, we are always expanding our capabilities so please do not hesitate to contact our technical sales team who will guide you through your enquiry.

Our Germanium Optics Include Germanium Infrared Lenses

Alongside our other germanium products, we specialise in providing custom germanium IR lenses, both stock and bespoke.

Germanium IR Lenses

Speak to our experts about your Custom Germanium Optics needs today

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    Optical Properties of Germanium

    Germanium (Ge) is a crystalline material with the highest index of refraction (4.0026 at 11µm) among frequently used infrared materials. Germanium’s high refractive index means that uncoated germanium can act as a natural 50% beamsplitter between 2 and 14µm. It also has a comparatively high hardness and density, making it an ideal substrate in optical systems requiring a more robust infrared optical component.

    With our in-house state-of-the-art metrology laboratory, you can be confident that your germanium optical components, whether it’s a germanium window or a germanium IR lens, will meet your requirements. You can find out more about our testing facilities here.

    Transmission Range1.8 to 23µm
    Refractive Index4.002 @ 11µm
    Density5.33 g/cm3
    Melting Point936°C
    HardnessKnoop 780
    Operating Temperature< 100°C
    Diameter5mm to 300mm +
    Form error (@633nm)< 0.5 waves
    Centration/parallelism< 1 arc minute
    Scratch/dig< 60/40
    Typical coatingsAR/AR — T(avg) > 85% @ 3-12µm, AR/DLC — T(avg) > 85% @ 7-14µm
    Graph to depict the optical properties of Germanium, uncoated uncoated 1mm thick

    Uncoated, 1mm thick

    Graph to depict the optical properties of Germanium, uncoated AR/AR @ 3-12µm

    AR/AR @ 3-12µm

    Graph to depict the optical properties of Germanium, uncoated AR/DLC @ 7-14µm

    AR/DLC @ 7-14µm

    Frequently Asked Questions

    Germanium Optics are those manufactured from germanium (Ge), a high refractive index crystalline material, which is transparent in the infrared waveband, particularly the mid-wave infrared (MWIR) and long-wave infrared (LWIR) regions making it an ideal material for lenses and windows used in thermal imaging and infrared spectroscopy.

    Germanium and Silicon are both semiconductor crystalline materials that exhibit distinct optical properties. Whereas Germanium Optics are more commonly used in MWIR and LWIR thermal imaging applications, Silicon Optics are more often used in applications utilising NIR wavelengths. The two materials are comparable in their transmission and refractive indices, Silicon is half as dense and therefore can be used in optical applications which are weight-sensitive.

    Germanium lenses perform over a broad wavelength range in the infrared region from 1.8µm to 23µm, making them suitable for thermal imaging applications. They also have a high refractive index for effective focusing of light and as such exhibit a low dispersion which reduces the chromatic aberrations, which is crucial in an imaging system as it means better image quality.

    For an optical system working within the infrared region, germanium infrared lenses are an excellent choice due to their broad wavelength range encompassing both the mid-wave infrared (MWIR) and long-wave infrared (LWIR) thermal wavebands. Germanium’s high refractive index, compared to many other optical materials, allows for more efficient focusing of light and means the lens exhibits a low optical dispersion which minimises chromatic aberrations. The transmission performance and durability of germanium lenses can also be optimised by applying antireflective (AR) and diamond-like carbon (DLC) coatings.

    The refractive index for Germanium (Ge) is 4.002 at 11µm.

    The resistivity of germanium can affect the transmission of light in the infrared spectrum. The lower the resistivity the more the material will absorb the light and therefore germanium’s transmission will decrease. Consequently, the higher the resistivity the higher the transmission in the infrared region which is ideal for when germanium lenses and germanium windows are being used in optical applications.

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    We are ready and waiting to answer any queries you may have about germanium.

    Additional Information

    Low optical distortion

    Due to germanium’s high refractive index, spherical germanium lenses have a low optical dispersion and therefore display minimal chromatic aberration.

    Eliminate spherical aberration

    Aspheric germanium lenses offer diffraction-limited performance. Their design eliminates spherical aberration and can therefore greatly simplify an optical system by removing the need for multiple elements.

    Substrate for infrared longpass

    Germanium optics are often used as a substrate for infrared longpass filters as it naturally blocks the UV and visible wavelengths. It is a semiconducting material and therefore has an abrupt cut-on (intrinsic edge) at 1.7µm.

    Naturally high reflectivity

    Due to germanium’s naturally high reflectivity, AR coatings are usually applied to increase transmission, reaching over 85%. A DLC coating can be applied to an exposed surface, increasing durability and transmission.


    High density

    Germanium has a high density which needs to be taken into account if the optical system is weight-sensitive. Silicon has almost half the density of germanium so could present a better option if weight is an issue.

    Thermal runaway

    It is also subject to thermal runaway – as the temperature increases, germanium’s absorption also increases, meaning its transmission is reduced. At 100°C, it is almost opaque, and by 200°C, it does not transmit at all. Therefore it should be used in systems working below 100°C to reduce the risk of optical failure

    Hazardous dust (if inhaled)

    Germanium dust is hazardous if inhaled, so care should be taken when handling.

    Typical Applications

    Infrared Lenses for FLIR Thermal Imaging

    FLIR & Thermal Imaging

    Germanium optics transmit in both the MWIR and LWIR wavebands, making it ideal for thermal imaging systems both as protective windows and/or lenses within the systems.

    Infrared Lenses for Low Powered CO2 Lasers

    Low-powered CO2 lasers

    Germanium transmits at 10.6µm and therefore works in a CO2 laser system. However, it cannot withstand the higher-powered lasers; zinc selenide is more commonly used here.

    Germanium for Fourier Transform Infrared Spectroscopy (FTIR)

    Fourier Transform Infrared Spectroscopy (FTIR)

    Germanium is often the material of choice for attenuated total reflection (ATR) prisms used in FTIR spectroscopy. It is especially used when the sample being measured has a high refractive index.

    Germanium for Pyrometers


    Due to germanium’s comparative robustness, especially when a DLC coating has been applied to the exposed surface, it is commonly used as a protective window in pyrometers.

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    With our in-house state-of-the-art metrology laboratory you can be confident that your optical components will meet your requirements. You can find out more about our testing facilities here.

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