THE ROLE OF LASER COHERENCE LENGTH IN CONTINUOUS-WAVE COHERENT LASER-RADAR

The effect of laser coherence length on the performance of continuous- wave coherent laser radar (lidar) is examined. A laboratory lidar inve stigation using semiconductor lasers with linewidths of the order of 1 MHz has been carried out for ranges much shorter than, comparable wit h and much longer than the laser coherence length (about 50 m). The si gnal strength, spectrum and fluctuation statistics are all shown to be sensitive to the various effects resulting from limited laser coheren ce. Different laser line-broadening mechanisms are considered, includi ng phase diffusion and jitter, and the fundamental difference between single- and multiple-mode sources is examined. Limited laser coherence is also shown to give rise to an excess noise contribution, and this can be severely detrimental to the lidar system performance.