Browsing by Subject "diode lasers"

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Ammonia monitoring near 1.5µm with diode-laser absorption sensors
(Optical Society of America, 2001-04-20) Webber, Michael E.; Baer, Douglas S.; Hanson, Ronald K.; Webber, Michael E.
We investigated ammonia spectroscopy near 1.5 µm to select transitions appropriate for trace ammonia detection in air-quality and combustion emissions-monitoring applications using diode lasers. Six ammonia features were selected for these trace-gas detection applications based on their transition strengths and isolation from interfering species. The strengths, positions, and lower-state energies for the lines in each of these features were measured and compared with values published in the literature. Ammonia slip was measured in the exhaust above an atmospheric pressure premixed ethylene–air burner to demonstrate the feasibility of the in situ diode-laser sensor.
Fiber-amplified-enhanced photoacoustic spectroscopy with near-infrared tunable diode lasers
(Optical Society of America, 2003-04-20) Webber, Michael E.; Pushkarsky, Michael B.; Patel, C. Kumar; Webber, Michael E.
A new approach to wavelength-modulation photoacoustic spectroscopy is reported, which incorporates diode lasers in the near infrared and optical fiber amplifiers to enhance sensitivity. We demonstrate the technique with ammonia detection, yielding a sensitivity limit less than 6 parts in 109, by interrogating a transition near 1532 nm with 500 mW of output power from the fiber amplifier, an optical pathlength of 18.4 cm, and an integration time constant of 10 s. This sensitivity is 15 times better than in prior published results for detecting ammonia with near-infrared diode lasers. The normalized minimum detectable fractional optical density,α min l, is 1.8 x 10-8; the minimum detectable absorption coefficient, α min, is 9.5 x 10-10 cm-1; and the minimum detectable absorption coefficient normalized by power and bandwidth is 1.5 x 10-9 W cm-1/ √Hz. These measurements represent what we believe to be the first use of fiber amplifiers to enhance photoacoustic spectroscopy, and this technique is applicable to all other species that fall within the gain curves of optical fiber amplifiers.
In situ combustion measurements of CO2 by use of a distributed-feedback diode-laser sensor near 2.0µm
(Optical Society of America, 2001-02-20) Webber, Michael E.; Kim, Suhong; Sanders, Scott T.; Baer, Douglas S.; Hanson, Ronald K.; Ikeda, Yuji; Webber, Michael E.
High-resolution absorption measurements of CO2 were made in a heated static cell and in the combustion region above a flat-flame burner for the development of an in situ CO2 combustion diagnostic based on a distributed-feedback diode laser operating near 2.0 um. Calculated absorption spectra of high temperature H2O and CO2 were used to find candidate transitions for CO2 detection, and the R(50) transition at 1.997 um (the v1 + 2v2 + v3 band) was selected on the basis of its line strength and its isolation from interfering high-temperature water absorption. Measurements of spectroscopic parameters such as the line strength, the self-broadening coefficient, and the line position were made for the R(50) transition, and an improved value for the line strength is reported. The combustion-product populations of CO2 in the combustion region above a flat-flame burner were determined in situ to verify the measured spectroscopic parameters and to demonstrate the feasibility of the diode-laser sensor.
Measurements of NH3 and CO2 with distributed-feedback diode lasers near 2.0 µm in bioreactor vent gases
(Optical Society of America, 2001-08-20) Webber, Michael E.; Claps, Ricardo; Englich, Florian V.; Tittel, Frank K.; Jeffries, Jay B.; Hanson, Ronald K.; Webber, Michael E.
Measurements of NH3 and CO2 were made in bioreactor vent gases with distributed-feedback diode-laser sensors operating near 2 um. Calculated spectra of NH3 and CO2 were used to determine the optimum transitions for interrogating with an absorption sensor. For ammonia, a strong and isolated absorption transition at 5016.977 cm-1 was selected for trace gas monitoring. For CO2, an isolated transition at 5007.787 cm-1 was selected to measure widely varying concentrations [500 parts per million (ppm) to 10%], with sufficient signal for low mole fractions and without being optically thick for high mole fractions. Using direct absorption and a 36-m total path-length multipass flow-through cell, we achieved a minimum detectivity of 0.25 ppm forNH3 and 40 ppm for CO2. We report on the quasi-continuous field measurements of NH3 and CO2 concentration in bioreactor vent gases that were recorded at NASA Johnson Space Center with a portable and automated sensor system over a 45-h data collection window.