Asymptotic evolution of speckle patterns to synthesize non-homogeneous string beams

We analyze the evolution of the speckle pattern subjected to a compression showing that the spatial evolution of the probability density function satisfies a non-linear diffusion equation. Its asymptotic solution corresponds to a non-homogeneous wave with string-shape. During the compression, an irradiance interaction is generated between the speckles. The interaction satisfies a type-logistic equation. The electric field components associated with the speckles present a random behavior, however, during the compression process, the transversal components cancel each other, and the resulting light presents a state of polarization parallel to the propagation coordinate, justifying the non-homogeneous behavior. Computer simulations are presented.