DEVELOPMENT AND EVALUATION OF A TUNABLE DIODE LASER ABSORPTION SPECTROMETER FOR TRACE HUMIDITY MEASUREMENTS

摘要

A tunable diode laser absorption spectrometer has been developed and evaluated by a European consortium. The spectrometer uses a distributed feedback diode laser to access a strong water vapour absorption at 1393 nm. In tests over the humidity range 1 ppm_(v) to 100 ppm_(v), the system showed a reproducibility of ±5%. The minimum detection sensitivity was estimated to be 25 ppb_(v). In addition, the dynamic response of the system was investigated, as well as its cross-sensitivity to other gas species including N_(2), He and CH_(4). After modification to the electronics, a reproducibility of 12 ppb_(v) was observed in the range 15 ppb_(v) to 1 ppm_(v) over a 3-month period.