Scattering of Poincaré beams: polarization speckles

Polarization speckle is a fine granular light pattern having spatially varying random polarization profile. We generate these speckle patterns by using the scattering of Poincaré beams, a special class of vector vortex beams, through a ground glass plate. Here, the Poincaré beams are generated using a polarization sensitive spatial light modulator displaying an on-axis hologram corresponding to an optical vortex phase profile. The different inhomogeneities of the rough surface experience different polarizations, which control the ability for scattered waves to interfere at the detection plane and causes a spatially varying polarization profile. We experimentally determined the spatial variation of local degree of polarization and orientation of the polarization ellipse for these speckle patterns from the Stokes analysis. We also determined the size of scalar speckles using the auto-correlation function of Stokes parameter S₀ and the size of polarization speckles using the sum of auto-correlation functions of remaining three Stokes parameters. We found that the change in scalar speckle size with the index of the vector beam is very small and of the order of 1 pixel size of the camera but the size of polarization speckles decreases with the increase in index of the vector beam.