The dependence of the intensity PDF of a random beam propagating in the maritime atmosphere on source coherence

Measurements of intensity statistics of a spatially pre-randomized laser beam propagating in a turbulent atmosphere along two horizontal links in close proximity to grassy ground and above a creek have been carried out in the fall of 2012. The pre-randomization of the laser beam was made by using a nematic Spatial Light Modulator placed at the laser source exit. The beam's phase is randomized with Gaussian statistics with zero mean and fully controllable degree of coherence. The receiver consisted of an amplified photodetector and data acquisition device which were used to capture the beam intensity fluctuations after propagation through turbulent media. The results for the intensity Probability Density Function (PDF), the Cumulative Distribution Function and, in particular, for the scintillation index are presented for a variety of the source's states of coherence and environmental conditions. The analytical PDF is reconstructed from the statistical moments of intensity with the help of the Gamma-Laguerre model. The results clearly illustrate the dependence of the shapes of the density functions on the level of the source's degree of coherence and on environmental parameters. It is shown that the optimal source coherence level may be experimentally found to obtain the narrowest profile for the intensity PDF.