LONG-ATMOSPHERIC-PATH MEASUREMENTS OF NEAR-VISIBLE ABSORPTION-LINES OF O2 ISOTOPES AND H2O WITH A PROTOTYPE ALGAAS LASER TRANSCEIVER SYSTEM

Near-visible absorption lines of ambient H2O vapor and normal and heavy isotopes of O2 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 O2 isotopes to within 2%, which is similar to the accuracy with which the column densities were known. Measurements of O-16(2) linewidths and line strengths were made, and they agree with literature values to within experimental error. The detection sensitivity for (OO)-O-16-O-18 was found to be 0.1 part in 10(6) atm. km, corresponding to an absorbance sensitivity of 1 x 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).