L. I. Davis

Hydroxyl Radical Concentrations Measured in Ambient Air

Diurnal variations in the hydroxyl radical concentration of ambient air were measured for the first time by the technique of laser-induced fluorescence.

Ground‐state population distribution of OH determined with a tunable uv laser

We have measured the ground‐state population distribution of OH in a flame by detecting the resonance fluorescence excited by a high‐power tunable uv laser beam. This technique provides spatial, temporal, and spectral resolutions which are not possible with absorption measurements involving conventional light sources. It should prove particularly valuable in studying the dynamics of combustion.

Laser‐induced dissociation of ozone and resonance fluorescence of OH in ambient air

In the measurement of hydroxyl (OH) concentrations in air using the technique of resonance fluorescence, it was established that the presence of ambient ozone led to significant interference. It is concluded that this is a result of OH formation due to laser‐induced dissociation of ozone. A reduction in the power density of excitation was required to reduce this effect to a negligible level.

Two‐photon dissociation of water: A new OH source for spectroscopic studies

We have observed the phenomenon of two−photon dissociation of water using a tunable uv laser beam and the generation of hydroxyl radicals (OH) as a dissociation product. This phenomenon affords a new way for measuring the quenching rates of electronically excited OH due to nitrogen, water, and other molecules under atmospheric conditions.

Shot noise limited detection of OH using the technique of laser induced fluorescence

This paper reports nearly shot noise limited detection of OH using the technique of laser-induced fluorescence. A lidar configuration is used to excite fluorescence in a large volume, and a narrow-bandwidth interference filter provides spectral discrimination. This arrangement alleviates the effect of ozone interference and facilitates image processing at relatively close distances. The detection limit is determined mainly by the shot noise of the solar background. Ground-based measurements in Dearborn indicate a detection limit of ~2 × 106 OH/cm3 over a 40-min acquisition period. In favorable conditions, a comparable detection limit is also expected for airborne measurements.

Heating of laser-induced plasmas in helium

Abstract This letter reports several observations on the heating of laser-produced plasmas in He. Agreement of a qualitative nature is noted between experiments and published theoretical predictions. The possibility of an instability in the transfer of energy from the radiation field to the electrons in the breakdown region is pointed out.