Knight Optical can supply a range of gas cells used as wavelength references or for chemical analysis in spectroscopic instruments such as Fourier transform infrared (FTIR) spectroscopy and laser absorption spectroscopy (LAS). There are two main optical components in a gas cell, the cylinder and the transmission windows. Below are some typical substrates used for these components:
Cylinder substrates include:
Transmission window substrates include:
· Fused quartz
· Soda lime float
· Other materials: aluminium
· Potassium bromide (KBr)
· Sodium chloride (NaCl)
· Calcium fluoride (CaF2)
· Zinc selenide (ZnSe)
The materials all transmit over a broad wavelength range, and the transmission windows transmit into the infrared waveband. Knight Optical can supply these windows separately, and can include a slight wedge to reduce interference.
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.
Contact our multilingual technical sales team and discover how Knight Optical’s high quality gas cells and service can improve your instrumentation and supply chain experience.
Typical materials used for windows in custom gas cells are:
Datasheet – IR Material Calcium Fluoride
IR material quartz crystal
IR material Sapphire_C-cut_UV
IR material zinc selenide
- The pathlength is the how far the incident beam travels through the gas. These are often termed as short, long or variable pathlengths.
- A short pathlength is sufficient for high concentration mixtures, for example, a reference cell filled with 100% methane.
- A long pathlength would be needed if the concentration of the gases is lower and often given as parts-per-billion (ppb), this would be needed when, for example, the levels of greenhouses gases are being measured in an air sample.
- Knight Optical can supply fixed or variable pathlength gas cells, where variable types used mirrors to increase the pathlength by reflecting the beam throughout the cell rather than straight through.
- There are also cell types for holding vapours and liquids. For example, our drilled cell windows can be used in demountable cell holders, which generally hold liquid samples.
- The flatness and irregularity of the transmission windows are tested on our Zygo Verifire XPZ interferometer, where we can also test the transmitted wavefront error of the window.
- We check the parallelism on our Trioptics PrismMaster which is accurate to 3 arc seconds.
- Transmission and reflection scans are conducted on our Agilent Cary 7000 Spectrophotometer which can perform spectral scans at multiple angles of incidence and different polarisations.
- We can then further test the infrared transmission on our Agilent Cary 660 FTIR spectrometer.
- All optics are 100% visually inspected before packaging, our staff are trained to ISO 10110 and MIL-0-13830A, and can check down to 10/5 scratch/dig which is especially critical in laser applications.