Polarization pattern of vector vortex beams generated by $q$-plates with   different topological charges
  We describe the polarization topology of the vector beams emerging from a patterned birefringent liquid crystal plate with a topological charge $q$ at its center ($q$-plate). The polarization topological structures for different $q$-plates and different input polarization states have been studied experimentally by measuring the Stokes parameters point-by-point in the beam transverse plane. Furthermore, we used a tuned $q=1/2$-plate to generate cylindrical vector beams with radial or azimuthal polarizations, with the possibility of switching dynamically between these two cases by simply changing the linear polarization of the input beam. 
Filippo Cardano, Ebrahim Karimi, Sergei Slussarenko, Lorenzo Marrucci,   Corrado de Lisio, and Enrico Santamato
physics.optics