Diode-laser absorption measurements of CO2, H2O, N2O, and NH3 near 2.0 μm

A diode-laser sensor has been developed for sensitive measurements of CO2, H2O, N2O, and NH3 concentrations in various flowfields using absorption spectroscopy and extractive sampling techniques. An external-cavity diode laser with a tuning range of 1.953-2.057 mu m was used to record absorption lineshapes from measured transitions in the CO2 4 nu(2)(0) + nu(3), nu(1 +) 2 nu(2)(0) + nu(3), and 2 nu(1) + nu(3) bands, H2O + nu(3) and nu(1) + nu(2) bands, N2O 2 nu(1) + 4(2)(0), nu(2)(1) + 2 nu(3), 3 nu(1) + 2 nu(2)(0), and 4 nu(1) bands, and NH3 nu(1) + nu(4) and nu(1) + nu(4) bands. Measured CO2, H2O, and N2O survey spectra were compared to calculations to verify the HITRAN96 database and used to determine optimum transitions for species detection. Individual lineshape measurements were used to determine fundamental spectroscopic parameters including the line strength, line-center frequency, and self-broadening coefficient of the probed transition. The results represent the first measurements of CO2, H2O, N2O, and NH3 absorption near 2.0 mu m using room-temperature near-IR diode lasers.