Correlations in Scattered Phase Singular Beams and their Applications

Abstract

This thesis deals with correlations present in scattered optical phase singular beams and the utilization of their propagation characteristics for extracting the mode information as well as other applications towards encryption and communication. We have generated the optical phase singular beams using computer generated holography technique which can be implemented with the help of a computer-interfaced spatial light modulator. For converting the vortex beams to Bessel-Gauss beams, we have used an axicon. Then we scatter or disturb the generated optical beams by scattering them through a rough surface such as ground glass plate. Further, we proceed for finding the correlations present in the scattered light beams and extracting the mode information. We have proposed and implemented a new scheme based on 2 D spatial auto-correlation function of scattered optical vortices for diagnosing the order of a perturbed vortex which is alignment free. The topological charge of a perturbed vortex beam is given by the number of dark rings present in its auto-correlation function. We have utilized the divergence of the first ring with respect to the propagation distance for diagnosing the order as the observation of the number of dark rings is difficult due to the decreased correlation strength with spatial separation distance (and#916;r) for higher order perturbed vortices. We have provided the exact analytical expression for 2 D spatial auto-correlation function and divergence of first ring. Our analytical results are good agreement with the obtained experimental results. We also study the observation of an exact number of rings depends on the total number of pixels, with the increase in the number of pixels used to find the 2 D autocorrelation function, can enhance visibility of rings. We have also found that the spatial mode information of the perturbed vortices can be extracted with the accuracy of 95% by comparing the experimentally obtained results with theoretical findings. newlineWe have studied the correlations present in scatte