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

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 mu m. A normalized noise equivalent absorptionvspace1pt coefficient, NNEA(1 sigma) = 1.4 x 10(-8) cm(-1)W/root Hz was obtained for CO2 using the R18 line of the 2(v1) + v(3) band at 4991.26 cm(-1). This corresponds to minimum detection limit (1 sigma) 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 v(3) +v(4) band at 4986.99 cm(-1). A detection limit (1 sigma) of 3ppm for NH3 concentration with a 1 s lock-in time constant was achieved. This results in a normalized noise equivalent absorption of NNEA(1 sigma) = 8.9 x 10(-9) cm(-1)W/root Hz.