Coherent Doppler Lidar using a Hybrid CO₂ Laser with a Low Pressure Gain Section below the Threshold

Abstract

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.