The Study of Geometric Phase in Twisted Crystal
  The polarization matrix ($2\times2$) obtained from two component eigen-spinors of spherical harmonics help us to evaluate the differential matrix $N$ of the anisotropic optical medium. The geometric phase is realized through {\it helicity} of photon, assuming the transmission of polarized light through the crystal which has been twisted about the normal to its surface over a closed path. 
Dipti Banerjee