OPTIMAL BEAM FORMING FOR LASER BEAM PROPAGATION ...

are the most important causes of all types of random media effects in wavepropagation and may happen all at once in one propagation case.AbsorptionWhen laser radiation is propagated in an absorbing medium, heating of themedium takes place and causes temperature gradients in the media. Thiseffect will in turn cause media density changes and result in refractive indexgradients being formed across the beam. These gradients act as a distributedlens which distorts the beam and decreases the peak intensity at thefocal point [39]. This self-induced distortion and spreading of the beam iscalled thermal blooming, which is commonly met in high power laser beampropagation [70, 54].ScatteringScattering is the direction redistribution phenomenon caused by rough surfaceor small particles in the media. Rayleigh scattering, Mie scattering, andnonselective scattering are common situations associated with different sizesof the scatter.The scattering effect of particles of matter was first studied by LordRayleigh, who studied the single scattering of a plane wave with a dielectricsphere in a vacuum and deduced that the color of the sky is the resultof stronger scattering in the radiation of shorter wavelengths [55, 46].Rayleigh’s scattering theory was extended by Mie, who considered light scatteringby spheres of different sizes, comparable with the wavelength of light,9