Carbon dioxide and ammonia detection using 2 μm diode laser based quartz-enhanced photoacoustic spectroscopy

Abstract

Quartz-enhanced photoacoustic spectroscopy was employed for trace gas concentration measurements of CO2 and NH3 using a continuous wave thermoelectrically cooled, distributed feedback diode laser operating at 2 μm. A normalized noise equivalent absorption coefficient, NNEA(1σ)=1.4×10-8 cm-1W/ √Hz was obtained for CO2 using the R18 line of the 2ν1+ν 3 band at 4991.26 cm-1. This corresponds to minimum detection limit (1σ) of 18 parts per million (ppm) for a 1 s lock-in time constant. The influence of the H2O presence in the sample gas mixture on the CO2 sensor performance was investigated. Ammonia detection was performed using the P P 6(6)S line of the ν3+ν4 band at 4986.99 cm-1. A detection limit (1σ) of 3 ppm for NH3 concentration with a 1 s lock-in time constant was achieved. This results in a normalized noise equivalent absorption of NNEA(1σ)=8.9×10-9 cm-1W/ √Hz. © Springer-Verlag 2007.