Differential absorption lidar (DIAL} with heterodyne detection is the most sensitive known technique for the remote sensing of trace concentrations of gases in the atmosphere. A DIAL system based on the CO2 laser holds the greatest near-term promise from the standpoints of efficiency, versatility, and reliability. To achieve maximum accuracy with such a system, the simultaneous provision of two frequencystabilized pulsed laser beams and two frequencystabilized cw laser beams is required. The proposed program is concerned with the development of a fieldable CO2 laser-based DIAL system with heterodyne detection. The system will employ a single CO2 gain tube to produce the two frequency-stabilized cw outputs as well as a single CO2 gain medium to generate the two frequency-stabilized pulsed outputs. During Phase I of this program, the relative merits of two concepts for a frequency-stabilized dual wavelength cw CO2 laser will be evaluated. The approach with the greater overall frequency and amplitude stability will be adopted as the local oscillator source for the DIAL system. Also during Phase I the crosssaturation behavior in a dual wavelength pulsed CO2 laser with a novel design to minimize the mutual interaction of the two laser lines will be evaluated.Anticipated Results/Potent al Commercial Applications as described by the awardee:It is anticipated that the end product of this research and development program will be a fully fieldable CO2 laserbased differential absorption lidar system with vastly improved sensitivity and accuracy over the existing systems. It should be capable of measuring trace gas concentrations down to 0.1 ppm up to a range exceeding 1 km at a sample rate of 50 points per second. Such a system will be suitable for monitoring the dispersion of tracer gases or pollutants released into the atmosphere. Parts of this system may also be useful in the ultra precise measurement of distances.
