Intensity correlations in scattered vector vortex beams for determining the topological charge

• A novel scheme for measuring the topological charge (TC) of the vector vortex beam (VVB) is proposed. • Non-separability of OAM and polarization of vortex beams is verified by measuring the degree of polarization. • The divergence of the polarization speckle size was measured for the topological charge of the vector vortices. • The decay factor is derived from an empirical fitting formula. We propose a novel scheme for measuring the topological charge (TC) of the vector vortex beam (VVB) using polarization speckles size of the 2D auto-correlation function of scattered vector vortices. We have generated the non-separable state having singularities in both orbital angular momentum (OAM) and polarization. This non-separability is verified by measuring the degree of polarization (DOP) which can be calculated by using Stokes parameters. The Stokes parameters can be measured by observing the intensity distribution of the beam when projected onto different polarization states. The divergence of polarization speckle size of the auto-correlation function was measured as a function of topological charge of the vector vortex beams. These results can be used to generate a security key for data authentication and data encryption.