Measuring the phase accumulation of a changing polarization state of light

We study a nonlinear geometric phase shift that arises when the po-

larization state of a light beam is continually transformed, known as the

Pancharatnam phase. We employ an interferometer containing a BaB₂O₄

birefringent crystal in one arm in order to transform the polarization state

of one of the split beams before recombining and measuring the output

intensity. We show that the accumulated phase change of the light wave

is manifested by the intensity of the final beam. We present experimental

measurements along with a model for this system based on the Poincare

sphere picture of polarization state space, in which the geometric phase

is proportional to the area bounded by the polarization state space path

taken by the beam, after being closed by a geodesic on the sphere.