Enhanced Direct-Detection of CO2 Lidar Returns Using a Laser Pre-Amplifier*

The relative merits and technical differences between direct-detection and heterodyne-detection for CO2 lidar are well known. Direct-detection offers enhanced information concerning the average intensity of the lidar returns but at the expense of reduced signal-to-noise level. Heterodyne detection requires an increase in system complexity, provides an enhancement in the S/N ratio of 4 to 6 orders of magnitude, but is limited in its ability to scan rapidly through several CO2 laser lines.