Detection of Doppler signal of moving target using 1.06 μm coherent detection lidar

The demo system using 1.06 μm coherent detection lidar for velocity measurement was introduced. One approach is to inject the laser of monolithic non-planar unidirectional ring laser into a high power Q-switch Nd:YAG laser to obtain pulsed and single-longitudinal-mode laser, simultaneity, to lock the frequency of the Q-switched laser to the master oscillator. Single frequency pulse laser with output power higher than 5 mJ was obtained, and pulse width was 40 ns. The Q-switched laser was used in a heterodyne system to measure the velocity of a turning object. The speed of moving target was observed by the ways of heterodyne detection which measured the Doppler information of moving target. The moving target was a dial whose rotate speed could be modulated between 0-60 Hz. The diameter of dial was 10 cm. The signals would be received by high speed photodiodes whose bandwidth was 3.5 GHz, and being sampled at the rate of 2.5 GS/s. The Doppler shift causing by moving target can be measured by the processing system based on LabVIEW. The comparative error of the velocity measurement was less than 3%. The error in the velocity measurement was analyzed in bandwidth of output laser and precision of system. The demo system provides a good repetition in velocity measurement.