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Infrared Gas Cells

Infrared Gas Cells

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Find out more about our custom infrared gas cells

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Knight Optical is the go-to supplier for an array of gas cells and infrared gas cells that serve as wavelength references or are used in chemical analysis.

These cells are essential components in spectroscopic instruments, including Fourier transform infrared (FTIR) spectroscopy and laser absorption spectroscopy (LAS).

At Knight Optical we can offer both complete gas cells as well as the individual components, including the transmission windows. Our gas cells can be provided unfilled, alternatively, if you require a reference gas cell, filled with a desired gas or gas mixture, we require information such as:

  • Gas mixture and the desired concentration(s). Commonly used gases for reference cells include methane (CH4), ammonia (NH3), hydrogen cyanide (HCN), and acetylene (C2H2). We can provide other reference gases so please enquire for further information.
  • Pathlength and whether this is fixed or variable.
  • Substrate for the transmission windows, though we can work with you to determine which material would be suitable.
Infrared Gas Cells

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    Typical Gas Cell Components

    A gas cell generally comprises two principal optical components: the cylinder and the transmission windows. We offer these components in a variety of substrates to meet your custom gas cell requirements, making us your reliable infrared gas analyser component supplier. We can provide cylinders manufactured from substrates such as sodalime glass, whilst our transmission windows can be manufactured from more specialised materials such as magnesium fluoride MgF2 and calcium fluoride CaF2.

    Below are some typical substrates used for these components.

    The materials used in our gas cells are designed to transmit over a broad wavelength range. Specifically, the transmission windows are engineered to transmit into the infrared waveband. Knight Optical can supply these crucial components separately and can even introduce a slight wedge to the windows to minimise interference. This makes us a versatile provider for your custom gas cell and infrared gas analyser needs.

    Cylinder substratePyrex
    Cylinder substrateBorosilicate
    Cylinder substrateFused quartz
    Cylinder substrateSoda lime float
    Cylinder substrateOther materials: aluminium
    Transmission window substratePotassium bromide (KBr)
    Transmission window substrateSodium chloride (NaCl)
    Transmission window substrateCalcium fluoride (CaF2)
    Transmission window substrateZinc selenide (ZnSe)

    Frequently Asked Questions

    Gas cells are used in infrared (IR) spectroscopy to contain the gas sample being analysed. Infrared radiation is transmitted through the gas sample to the detector. Depending on the material being analysed, different intensities of the transmitted wavelengths will reach the detector, as some is absorbed by the gas sample, and produce a unique spectrum.

    Knight Optical provides gas cells made up of two key components; the cylinder and the transmission window. The cylinder holds the gas that is used as for reference or to be analysed, typically there are gas inlet and outlet ports for the introduction and removal of the sample gas. The transmission window is manufactured from a material that transmits the desired wavelength range, often calcium fluoride (CaF2) or potassium bromide (KBr).

    Yes, by working closely with Knight Optical we can provide a custom IR gas cell that has been tailored to your specific requirements. 

    An infrared gas analyzer is a set of equipment that is used to measure gases in a sample by passing infrared radiation through it. An infrared gas cell is a key component in instrumentation such as this and will contain either a reference gas or the sample itself. 

    Infrared gas cells are used in a variety of applications including systems such as emission, environmental, and safety monitoring. They are widely used in gas analysis and detection equipment for industries including medical, astronomy, research, defence, and laboratory.

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

    Additional Information


    The pathlength describes the distance the incident beam traverses through the gas within the infrared gas cell. These are commonly categorised as short, long, or variable pathlengths, providing flexibility for your custom gas cell and infrared gas analyzer applications.

    High-Concentration Cells

    A short pathlength is ideal for high-concentration mixtures, such as a custom gas cell filled with 100% methane. This makes it a suitable choice for certain infrared gas analyzer applications.

    Low-Concentration Cells

    A long pathlength is required for low-concentration gases, often expressed in parts-per-billion (ppb), making it apt for measuring greenhouse gases in an air sample. This is particularly relevant for infrared gas analzser applications.

    Fixed vs Variable Cells

    Knight Optical offers both fixed and variable pathlength gas cells. The variable types utilise mirrors to extend the pathlength by reflecting the beam within the IR gas cell, rather than directing it straight through. This feature enhances the versatility of our custom gas cell offerings, making us a comprehensive solution.

    Vapour & Liquid Cells

    In addition to gas cells, Knight Optical also provides cell types suitable for holding vapours and liquids. For instance, our drilled cell windows can be integrated into demountable cell holders, which are generally used for holding liquid samples. This broadens our range of custom gas cell and infrared gas analyser solutions to meet your diverse analytical requirements.

    Quality Assurance

    Rigorous Window Testing

    The flatness and irregularity of our transmission windows are rigorously tested using our Zygo Verifire XPZ interferometer. This advanced equipment also allows us to test the transmitted wavefront error of the window, ensuring the highest quality for your custom gas cell applications.

    Precision in Parallelism

    We assess the parallelism of our transmission windows using our Trioptics PrismMaster, which boasts an accuracy of up to 3 arc seconds. This meticulous testing ensures the utmost precision for your custom gas cell and infrared gas analyser components.

    Advanced Spectral Scans

    Transmission and reflection scans are diligently carried out on our Agilent Cary 7000 Spectrophotometer. This advanced instrument is capable of performing spectral scans at multiple angles of incidence and various polarisations, offering exceptional versatility for your needs.

    Additional IR Testing

    Further testing of infrared transmission is conducted on our Agilent Cary 660 FTIR spectrometer. This adds an additional layer of verification, ensuring the highest quality for your custom gas cell components.

    Quality Control Standards

    All optics undergo a 100% visual inspection prior to packaging. Our staff are trained to ISO 10110 and MIL-O-13830A standards and are capable of inspecting down to a 10/5 scratch/dig level. This rigorous quality control is particularly crucial for infrared gas analysers and custom gas cell components, especially in laser applications.

    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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