Biomedical subjects

Douglas S Baer

Publications and source records attributed to Douglas S Baer.

3 recordsLinked to original sources

PubMed2005

Off-axis cavity ringdown spectroscopy: application to atmospheric nitrate radical detection.

Atmospheric nitrate radicals (NO3) are detected using off-axis cavity ringdown spectroscopy (CRDS) for the first time to our knowledge with a room-temperature continuous-wave (cw) diode laser operating near 662 nm. A prototype instrument was constructed that achieved a 1sigma absorption sensitivity of 5 x 10(-10) cm(-1) Hz(-1/2), corresponding to a 1.4 part per trillion by volume 2sigma detection limit in 4.6 s at 80 degrees C. This sensitivity is a significant improvement over a recent implementation of off-axis cavity-enhanced absorption spectroscopy and comparable to that of the most advanced cw CRDS and pulsed CRDS applications for atmospheric detection of NO3. A comparison of measurements of ambient air in Fairbanks, Alaska, recorded with the off-axis CRDS instrument and a previously characterized conventional cw CRDS instrument showed good agreement (R2 = 0.97).

Air Pollutants↗

PubMed2005

Cavity-enhanced quantum-cascade laser-based instrument for carbon monoxide measurements.

An autonomous instrument based on off-axis integrated cavity output spectroscopy has been developed and successfully deployed for measurements of carbon monoxide in the troposphere and tropopause onboard a NASA DC-8 aircraft. The instrument (Carbon Monoxide Gas Analyzer) consists of a measurement cell comprised of two high-reflectivity mirrors, a continuous-wave quantum-cascade laser, gas sampling system, control and data-acquisition electronics, and data-analysis software. CO measurements were determined from high-resolution CO absorption line shapes obtained by tuning the laser wavelength over the R(7) transition of the fundamental vibration band near 2172.8 cm(-1). The instrument reports CO mixing ratio (mole fraction) at a 1-Hz rate based on measured absorption, gas temperature, and pressure using Beer's Law. During several flights in May-June 2004 and January 2005 that reached altitudes of 41,000 ft (12.5 km), the instrument recorded CO values with a precision of 0.2 ppbv (1-s averaging time) and an accuracy limited by the reference CO gas cylinder (uncertainty < 1.0%). Despite moderate turbulence and measurements of particulate-laden airflows, the instrument operated consistently and did not require any maintenance, mirror cleaning, or optical realignment during the flights.

Journal Article↗

PubMed2004

Quantitative detection of singlet O2 by cavity-enhanced absorption.

A method for the practical determination of the absolute concentration of single (a1delta(g)) oxygen is discussed. The method is based on sensitive off-axis integrated-cavity-output spectroscopy (ICOS). Off-axis ICOS allows narrowband, continuous-wave lasers to be used in conjunction with optical cavities to record sensitive absorption measurements. The details of the method as well as spectroscopic data confirming the first observation of the (1, 0) band of the b1sigma(g)(+) - a1delta(g) Noxon system are presented. The absolute transition probabilities for the b1sigma(g)(+) - a1delta(g) Noxon system, which are not known precisely from experiments, are determined by quantum chemistry theory.

Journal Article↗