الفهرس 
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Abstract
The interaction of a powerful laser beam and an unguided channel (pure water and the clearest seawater) has been rigorously investigated. Thermal blooming phenomenon is studied through the ”beamwidth parameter” which is derived under a simple suitable closed form and accounts for the diffraction phenomenon both qualitatively and quantita¬tively. It is found that this parameter is a function of: propagation distance, initial beamwidth, wavelength, and laser power.
This investigation is concerned with the most clearest oceanic waters, which have their maximum transparency in the blue portion of the spectrum (400-500 pm). The optical parameterization of that water type is employed as the base¬line for the description of thermal blooming phenomenon in natural seawater. A step-by-step technique is employed taking into con¬sideration the thermal-dependence of the medium physical parameters and the coupling between the beam and the water along the propagation path. The beam divergence has been deeply analyzed in order to reduce it through the affecting set of parameters. Less distortion has been found for laser beams of larger diameter keeping laser power the same.