Molecules have specific absorption lines that depend on the specific molecular energy level transitions of the species. For gases, these lines are also particularly known (sub-picometer), narrow and insensitive to environmental conditions. A gas cell is simply a tube filled with a gas or a gaseous mixture of known chemical and isotopic purity and pressure and can be used as such or coupled to fiber optic cables. They have been widely studied as wavelength standards and are the basis of NIST SRM 2514, 2515, 2517, 2517A and 2519.
- Tunable laser
- Calibration of the detection system
- Reference for chemical detector or medical instrumentation
- Optical instrument calibration source (wavelength, dispersion, etc.).