Tunable Diode Laser Absorption Spectrometer Monitors the Ambient Methane with High Sensitivity

Tunable diode laser absorption spectroscopy(TDLAS) technique is a new method to detect trace-gas qualitatively or quantificationally based on the scan characteristic of the diode laser to obtain the absorption spectra in the characteristic absorption region.It needs to combine with a long absorption path in the ambient trace-gas measurements.It has a significant advantage not only in sensitivity but also in rapidity of response.The experimental results of monitoring of methane of the ambient air in a long time with a ground-based portable TDLAS system are described;it works with a room-temperature near infrared tunable diode laser to measure methane in the ambient air,the path length is lengthened by the multiple-reflection cell to lower the detection limit;and the second harmonic detection is used to lower the detection limit farther;the detection limit is below 0.087 mg/m~3,that is enough to the monitoring of ambient methane.