Phase Screen Modeling of Vortex Beam Propagation through a Turbid Medium

Laser-based applications leveraging coherent laser sources are subject to optical distortions created by random media containing random refractive index variations of various scale sizes. Refractive index fluctuations sizes comparable to the optical wavelength, due to small particles, create complex light-material interactions. Studying this particle interaction can be approached using statistical optics that model the coherence properties of the medium by the implementation of random phase screens. A phase screen represents a statistical realization of the optical phase shifts accumulated during propagation whose statistics are derived from a medium’s optical phase power spectrum. In this work, the phase power spectrum of a turbid medium is connected to the medium’s particle distribution by the medium’s volume scattering function by radiative transfer theory. This model is limited to small-angle forward scattering and small propagation geometries to prevent aliasing by high angle scattered light. Using this relationship, the statistics of the generated phase screens are studied and applied to the propagation of optical vortex beams through turbid water. Experimental orbital angular momentum mode spectrum measurements and intensity attenuation data are presented showing good agreement with the model. Furthermore, the validated phase screen model is shown to predict, as particle sizes increases, the effects of forward peaked scattering leading to vortex beam distortion.