Coherence characterization of a phase-lockedpartially coherent flat-topped array laser beampropagating through underwater turbulence

In this research, based on an analytical expression for Cross-Spectral Density (CSD)matrix elements, coherence properties of phase-locked partially coherent flat-topped(PCFT) radial array laser beams propagating through propagating through the clear waterturbulent ocean are explored. Due to the complicated nature of the oceanicturbulencespectrum, the analysis is restricted to numerical computations. The simulation is done byconsidering the effects of source parameters (such as radius of array setup’s circle,effective width of the spectral degree of coherence and wavelength) and turbulent oceanfactors (such as the rate of dissipation of the turbulent kinetic energyper unit mass offluid,  , and relative strength of temperature and salinity fluctuations,  , Kolmogorovmicro-scale,  , and rate of dissipation of the mean squared temperature, T ) in detail.Results indicate that, for off-axis propagation points, the spectral degree of coherencedegrades to a minimum value (zero at far field) with decreasing in the values of  and alongside with the increasing in the value of T , which are corresponding to increase inthe strength of oceanic turbulence. In addition, in oceanic media, PCFT array laser beamshaving the longer source’s correlation length, flatness order and wavelength or a smallerradius of array setup’s ring are found to be advantageous in the sense of slow degradationof the coherence degree at all propagation distances.

Keywords:

array laser beams , coherence , oceanic turbulence , underwater optical communication