Use of CO and CO(2) Lasers to Detect Pollutants in the Atmosphere

Several spectral coincidences between CO laser emission lines and infrared absorption lines of oxides of nitrogen have recently been observed. Using existing infrared spectroscopy data, we predict additional spectral coincidences; the Q-switched CO laser emits certain lines which overlap SO(2) absorption lines, and certain frequency-doubled CO(2) laser lines overlap NO and CO absorption lines. Other spectral overlaps involving the CO(2) laser have been reported elsewhere. Based on such coincidences remote sensing of these atmospheric constituents can be accomplished by observing resonant absorption, thermal emission, or fluorescence. We discuss sensitivities for each of these methods, using data on line strengths and pressure-broadened line widths. Wide band heterodyne receivers offer high sensitivity when they can be used; our discussion includes the use of this type of receiver system.