New improvements in methane detection using a Helmholtz resonant photoacoustic laser sensor: a comparison between near-IR diode lasers and mid-IR quantum cascade lasers.
Atmospheric methane was detected by combining a photoacoustic (PA) sensor with several lasers emitting in both the near- and mid-infrared spectral ranges to check the achievable detection limits. The PA spectrometer is based on differential Helmholtz resonance. Near-infrared telecommunication-type laser diodes of increasing power, from Sensors Unlimited Inc. and Anritsu, were first used to scan the 2 nu(3) band of CH(4) near 1.65 microm. The best achieved detection limit is 0.15 ppm of methane at atmospheric pressure and with a 1s integration time. The PA sensor was then operated in conjunction with a quantum cascade laser from Alpes Lasers emitting near 7.9 microm on the nu(4) band of CH(4). The achieved detection limit is then of 3 ppb. The dramatic improvement in the detection limit obtained with the QC laser is due to the stronger optical power as well as to the capability of reaching the fundamental bands of methane lying in the mid-infrared spectral range.
Grossel
Agnès
A
Groupe de Spectrométrie Moléculaire et Atmosphérique, UMR CNRS 6089, UFR Sciences Exactes et Naturelles, Moulin de la Housse, BP 1039, 51687 Reims, Cedex 2, France.
Zeninari
Virginie
V
Joly
Lilian
L
Parvitte
Bertrand
B
Courtois
Daniel
D
Durry
Georges
G
D000162:Acoustics; D000388:Air / Q000032:analysis*; D007834:Lasers; D008027:Light; D008697:Methane / Q000032:analysis*; D011789:Quantum Theory; D013055:Spectrophotometry, Infrared; D013057:Spectrum Analysis / Q000379:methods
D008697:Methane