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Picosecond pulsewidth direct detection lidar for imaging applications

In this paper, the development of a novel picosecond pulsewidth direct detection lidar for velocimetry and hard target imaging applications is discussed. The lidar system comprises of a high-speed fiber coupled laser, novel interleaved three-dimensional (3D) scanner, fiber coupled receiver with optical pre-amp module and a high-speed digitizer. The laser is a pulsed Erbium-doped fiber laser that operates at 1.55 microns wavelength, 10 MHz PRF, 60 picosecond pulse width and 8 W of output average power. The scanner is a multi-faceted polygon type that operates at scan speeds of 10000 lines per second. The system utilizes a state-of-the art 40 GS/s digitizer. The picosecond lidar allows high resolution volumetric measurement of temporally and spatially resolved 3D airspeeds in wind tunnels for capturing a 3D time-accurate map of aerosols or other seeding particles in the airflow using elastic backscatter from a rapidly scanned lidar beam with a narrow field-of-view. Preliminary testing inside wind tunnel has generated promising results for aerodynamic applications including visualizing flow characteristics around test targets. The lidar provided dynamic measurements of complex flow, including the downstream evolution of a wing tip vortex. A 3D image processing algorithm was used to correlate the motion of aerosol features between successive frames and to extract 3D airflow profiles. In this paper, details of lidar instrumentation configuration is discussed followed by results of high-speed 3D hard target imaging of various test targets.