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/\(\sqrt{\text{Hz}}\) was obtained for CO2 using the R18 line of the 2ν1+ν3 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 PP6(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/\(\sqrt{\text{Hz}}\).
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