Long-atmospheric-path measurements of near-visible absorption lines of O_2 isotopes and H_2O with a prototype AlGaAs laser transceiver system

Near-visible absorption lines of ambient H(2)O vapor and normal and heavy isotopes of O(2) have been measured over atmospheric paths of up to 0.46 km by using two wavelength-modulated, line-locked AlGaAs laser sources with a retroreflector-telescope system. The absolute signal levels agree with theoretical calculations for the O(2) isotopes to within 2%, which is similar to the accuracy with which the column densities were known. Measurements of (16)O(2) linewidths and line strengths were made, and they agree with literature values to within experimental error. The detection sensitivity for (16)O(18)O was found to be 0.1 part in 10(6) atm. km, correspondingto an absorbance sensitivity of 1 × 10(-5). It is concluded that atmospheric trace-gas sensing will be feasible with this apparatus over distances of several kilometers and at levels under 1 part in 10(6).