Tunable Diode Laser Absorption Spectroscopy (TDLAS) uses semiconductor lasers to perform gas sensing at IR wavelengths. The immediate goal is to detect methane -- a greenhouse gas. Because of the expected rise in the use of natural gas, it will be important to monitor methane concentrations in the atmosphere.

The instrument uses a single mode diode laser whose wavelength is modulated around an absorption line of the gas. A photodiode and lock-in amplifier detect the second harmonic signal, which is proportional to the gas concentration. The expected sensitivity of this technique is not high, but it should be suitable for source monitoring. Other gases that can be detected using this technique are NH3, CO, and CO2.