Photoacoustic spectroscopy for trace gas detection with cryogenic and room-temperature continuous-wave quantum cascade lasers

摘要

The main characteristics that a sensor must possess for trace gas detection and pollution monitoring are high sensitivity, high selectivity and the capability to perform in situ measurements. The photacoustic Helmholtz sensor developed in Reims, used in conjunction with powerful Quantum Cascade Lasers (QCLs), fulfils all these requirements. The best cell response is # 1200 V W~(c-m and th1e corespondin)g ultimate sensitivity is j 3.3x10~(T-WH1.his e1ficciezmt se2n0~s~or is( u-s()e1)d w)-ith mid-infrared QCLs from Alpes Lasers to reach the strong fundamental absorption bands of some atmospheric gases. A first cryogenic QCL emitting at 7.9 μm demonstrates the detection of methane in air with a detection limit of 3 ppb. A detection limit of 20 ppb of NO in air is demonstrated using another cryogenic QCL emitting in the 5.4 μm region. Real in-situ measurements can be achieved only with room-temperature QCLs. A room-temperature QCL emitting in the 7.9 μm region demonstrates the simultaneous detection of methane and nitrous oxide in air (17 and 7 ppb detection limit, respectively). All these reliable measurements allow the estimated detection limit for various atmospheric gases using quantum cascade lasers to be obtained. Each gas absorbing in the infrared may be detected at a detection limit in the ppb or low-ppb range.