Observation of the non-cyclic Pancharatnam–Berry phase in monolayer ReSe₂

We present, to our knowledge, the first experimental evidence of polarization conversion, wherein a particular polarized Gaussian light beam transmitted through the anisotropic mono-layered (ML) rhenium diselenide (ReSe 2 ) transforms linearly (circularly) polarized light into circular (linear) polarization. It is the development of incident angle-dependent linear and circular birefringence that allows the polarization conversion to occur in a controlled manner. Additionally, we introduce the Stokes polarimetric technique, a simplified methodology, to identify the non-cyclic Pancharatnam–Berry geometric phase (PBGP) that results from in-plane anisotropy of ML ReSe 2 . Compared to other approaches, such as the interferometric method, this one offers a number of benefits, including simple alignment for GP evaluation. Interesting features of PBGP have been demonstrated, and these could find use in GP-controlled optical sensors and switches. Furthermore, in-plane and out-of-plane beam centroid displacements of sub-wavelength order are calculated using Stokes parameters that resulted from optical spin-orbit interactions during transmission. In view of the tremendous current research interest in optical spin-orbit interactions and related phenomena manipulated by exotic properties of materials, we believe that our results will find novel applications in polarization optics and nanophotonics.