Comparison of Single Line and Broad-Spectrum Gaussian Beam Propagation Through Turbulence

Propagation of laser beams through a turbulent atmosphere over extended ranges can cause significant beam scintillation and wander which can degrade the effectiveness of a Free Space Optical (FSO) link. The use of a spectrally broadband laser light source, with a high spatial coherence and short temporal coherence, could lead to improved performance in one or both of these areas. This experiment investigates the effect of temporal coherence on the far-field turbulence induced effects on the beam. Narrow linewidth coherent sources were compared against a broadband source over a 13.5 km slant-path. The path was instrumented with a path averaged turbulence monitoring device during data collection along with a range of other meteorological parameters to predict atmospheric parameters. Target board beam profile data was collected to measure the spatial statistics due to atmospheric turbulence along with silicon detectors to measure the temporal statistics of the atmospheric turbulence effects. This data is analyzed and compared to full diffraction wave propagation simulation results. Our analysis shows the benefit that the broadband source does not suffer as many scintillation effects as the narrow-linewidth sources.