Absorption Tubes

In addition to our fiber-coupled cells, Wavelength References also offers bare absorption tubes.  These tubes are useful for free space optical applications, such as those that require wavelengths where optical fiber is not applicable.  We have many gases available and can provide mixtures as well.  For example, our customers often request a backfill of nitrogen to mimic atmospheric conditions.

Tubes are made custom to order so several configurations are possible.  When requesting an absorption tube, you may refer to our handy Absorption Tube Info Sheet.  Of course, please contact us with any questions.  We’d be eager to hear about your application!








Below you will find a drawing and general specifications and configurations for our glass tubes.  For our copper tubes (useful for caustic gases such as HF), please contact us.


Absorption Tube

Sketch of an absorption tube. Note: this drawing is not to scale.


  • Length: 2cm < L < 20cm (2cm, 5cm, 10cm standard)
  • Outer Diameter (OD): 12mm and 25mm standard; 5mm and 9mm also available
  • Tipoff: T < 10mm
  • Window Tilt: 3 degrees
  • Window Wedge: 0.3 degrees
  • Window material:  B270 Crown Glass (<2.6 microns); MgF2 (<8 microns); ZnSe (<14 microns)

Window Material

< 2.6 microns:  We supply wedged B270 Crown glass windows AR-coated for 600, 1330, 1550 or 1700nm.  AR-coatings are provided at no extra charge.

Mag. Fluoride Transmission Spectrum


< 8 microns:  We supply wedged MgF2 windows.  These provide excellent transmission and are lower cost than our ZnSe windows.  They are available for our 12mm and 25mm outer diameter tubing.  Click on the thumbnail for the transmission spectrum (graciously supplied by Crystran Ltd)




ZnSe Transmission Spectrum


< 14 microns:  For applications past 8 microns, we use ZnSe windows.  Click on the thumbnail for the transmission spectrum or visit Crystran.