Trace gas detection at atmospheric pressure using tunable diode lasers

Tunable diode lasers (TDL) are widely used for the detection of trace gases and pollutants in the atmosphere. In many of these applications, the gas sample flows through a multipass cell at reduced pressure (~30 Torr), and the resulting narrow IR absorption lines can be detected with very high sensitivity. Infrared absorptions of 1 part in 10 5 can be observed over path lengths of 100 m, giving noise levels equivalent to absorption coefficients of 10 −7 m −1 .