Conversion of a basis-dependent superposition of orbital-angular-momentum states using aqplate

Abstract

Stokes parameters play a vital role in the study of photons, electrons, and other elementary particles. Superposition of phase singularities in an orthogonal polarization basis leads to the creation of Stokes singularities. It has been established that these phase singularities carry orbital angular momentum of light and hence the study of Stokes singularities is significant. The superposition of orbital-angular-momentum states, depending on the chosen basis, leads to the formation of different types of Stokes singularities such as polarization singularities and Poincar\'e singularities. These are subsets of Stokes singularities. There is a plethora of applications that has emerged in recent years for both phase and polarization singularities. Spin to orbital-angular-momentum conversion is possible by the use of a $q$ plate. In fact, a $q$ plate can convert a scalar beam into a phase or polarization vortex and a polarization singularity into another polarization singularity. But the process of the inter- or intraconversion of Stokes vortices has not been reported so far. This article discusses this aspect and the invariance of various topological parameters that occur in this process.