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Custom Calomel

infrared calomel

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Knight Optical is a leading provider of precision optical components, including those made from calomel, a mercurous chloride (Hg2Cl2) crystalline material known for its wide transmission range and remarkable properties.

Calomel, with its exceptional transmission range from 0.38µm to 17µm, is renowned for its applications in infrared optics, making it a preferred choice for specialists seeking materials with specific calomel properties.

The calomel transmission range enables its use across visible to the long-wave infrared (LWIR) region, highlighting why calomel is so valued in calomel infrared optics. Its strong birefringence of Δn=0.683 and optically positive nature (ne > no) underscore its unique calomel properties. The material’s high extinction ratio between 2.5 to 17µm (ER > 1:15000) and a high figure of merit, M2, for acousto-optical devices further showcase what calomel is used for in advanced optical applications.

What is calomel used for?

Calomel excels in infrared polarisation and acousto-optical components. It stands out as one of the few materials suitable for LWIR applications demanding high performance in calomel refractive index and calomel transmission range.

Calomel is used in a variety of optical components. Broad calomel uses include:

  • Glan-Foucault polariser
  • Wollaston polariser
  • Polarising beamsplitters
  • Acousto-optical tunable filters

Furthermore, we’re capable of custom-manufacturing optical components such as prisms, windows, cubes, blocks, and wedges to meet specific requirements, thanks to calomel’s various properties.

infrared calomel

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    Optical Properties and Metrology Testing

    With our advanced metrology laboratory, customers can have complete confidence in the quality and performance of their calomel infrared optics components, ensuring they meet the exact calomel properties necessary for their applications. Discover more about how our testing facilities here.

    Below is a summary of Calomel’s optical properties.

    Transmission Range0.38 to 15µm
    Refractive Indexno 2.122, ne 3.190, Δn=+1.068 @ 380 nm
    Refractive Indexno 1.950, ne 2.548, Δn=+0.598 @ 700 nm
    Refractive Indexno 1.900, ne 2.449, Δn=+0.549 @ 3500 nm
    Refractive Indexno 1.890, ne 2.445, Δn=+0.547 @ 10 000 nm
    Density7.19 g/cm3
    Melting Point525°C
    Hardness1.5 Mohs
    Operating Temperature-5°C to 60°C

    Frequently Asked Questions

    Calomel, chemically known as mercurous chloride (Hg2Cl2), is a mineral and chemical compound historically used in various applications, including medicine, as a purgative and in the treatment of syphilis. In modern times, its usage has shifted primarily to scientific fields, such as electrochemistry, where calomel serves as an electrode in calomel reference electrodes, and in some niche optical applications due to its specific transmission and reflective properties.

    In infrared optics, calomel has been explored for its potential use due to its specific transmission characteristics in the infrared range. While not as common as other materials, calomel can be utilized in specialized optical components where its unique infrared transmission properties are advantageous, particularly in certain spectroscopic and analytical applications requiring material with specific infrared responses.

    Notable properties of calomel that may influence its suitability for optical applications include its low refractive index and unique transmission range, particularly in the infrared spectrum. However, its application in optical systems is limited compared to more conventional optical materials due to factors like toxicity and chemical stability. Its usage is typically confined to specific, controlled environments where its distinct properties can be safely and effectively employed.

    Calomel’s transmission range is primarily in the infrared region, although it is not commonly used in standard optical components due to safety and environmental concerns. In specialized cases where calomel is used, its transmission range is considered for applications that require specific infrared wavelengths, such as certain types of spectroscopy or chemical analysis, where its unique transmission properties may be beneficial.

    The refractive index of calomel is a crucial optical property that influences how light is transmitted and refracted through the material. While exact values may vary based on the spectral range and conditions, understanding calomel’s refractive index is essential for designing and implementing it in specific optical systems, particularly in specialized environments where its unique optical properties are required.

    While Knight Optical does not specifically advertise calomel components due to its rare and hazardous nature, custom fabrication of optical materials typically depends on the material’s applicability, safety, and environmental impact. For materials like calomel, which are less common and have significant health and safety considerations, customization would be highly specialized and subject to stringent regulations. Typically, the optical industry prefers safer, more stable alternatives for infrared applications, such as germanium or silicon, especially for commercial and research purposes.

    Is your question not here?

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

    Additional Information


    The first single crystal of calomel was produced in 1969 in the Czech Republic.


    The birefringence it exhibits is the highest known for a crystalline material, almost four times higher than calcite.

    Extinction Ratio

    The extinction ratio it exhibits in the IR region is >1:15000.

    Safety Data Sheet

    Calomel’s safety data sheet is available here.

    Typical Applications

    Germanium for Fourier Transform Infrared Spectroscopy (FTIR)

    Infrared Spectroscopy

    Retarder plates

    MWIR Polarisers and Waveplates

    Calomel for Acousto-Optics Devices

    Acousto-Optical Devices

    Aspherical Lenses for Laser Beam Shaping

    Laser Damage

    Laser systems have a CW laser damage resistance.

    Get in touch with us:

    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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