Off-axis average transmittance and beam spread of a partially coherent flat-topped beam in a turbulent underwater medium.

Abstract

The effects of oceanic turbulence on the off-axis optical transmittance and beam spread are examined when a partially coherent flat-topped beam wave propagates in an underwater medium. To observe the oceanic turbulence effect, the power spectrum of homogeneous and isotropic oceanic water combining the effects of salinity and temperature is used. Employing the extended Huygens-Fresnel integral and Carter's definition for the general beam formulation that is applied to a partially coherent flat-topped beam, the effects of the parameters of power spectrum, the link on the off-axis average transmittance, and beam spread are analyzed. The results obtained with the help of the MATLAB program indicate that if the flatness of the optical beam increases, the average transmittance increases, and the beam spread decreases. Partial coherence is found to be inversely proportional to the average transmittance and directly proportional to beam spread. Increase in the source size is found to increase the average transmittance and to reduce the beam spread. Loss of the kinetic energy of fluid causes less turbulence. The rate of dissipation of kinetic energy per unit mass of fluid is directly proportional to the average transmittance, while it is inversely proportional to the beam spread. The rate of dissipation of the mean square temperature is inversely proportional to the average transmittance and directly proportional to the beam spread. When the temperature-induced optical turbulence is dominant, the average transmittance almost never decreases. However, the salinity-induced optical turbulence sharply reduces the average transmittance and increases the beam spread of the partially coherent flat-topped beam in underwater turbulence. When the off-axis parameter becomes larger, average transmittance decreases.