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A coherent Doppler lidar has been developed using a hybrid CO2 laser with a low pressure gain section below the threshold. The CO2 laser oscillates in a single longitudinal mode with a modelimiting low pressure gain cell within its cavity. The offset frequency between the hybrid CO2 pulse laser and the local oscillator cw CO2 laser is controlled by monitoring the heterodyne IF beat frequency of the hybrid CO2 laser pulse scattered from lidar mirror surfaces. Configuration for the lidar system is simpler than that for the recently developed coherent lidar with an injection-locked TEA CO2 laser. Lidar performance was evaluated by observing wind vector profiles in the boundary layer. Wind variation caused by a sea breeze front was observed in the evaluation. Despite the lidar performance, much effort is needed to decrease the chirp of the hybrid laser, since the laser has a high frequency chirp within a pulse. Otherwise, it might be preferable to use another laser with much less chirp to improve lidar reliability.

Coherent Doppler Lidar using a Hybrid CO<sub>2</sub> Laser with a Low Pressure Gain Section below the Threshold