Geometric phase, also known as Berry’s or Pancharatnam phase, is the phase that accumulates when a wave or wave-like particle makes a closed-loop course and in optics, examples of geometric phase occur when studying angular momentum. A circularly-polarized beam imparts torque associated with /spin/ angular momentum, which describes the rotating direction of electric field oscillation. Additionally, light can also have intrinsic /orbital/ angular momentum (OAM) due to helical phasefronts, where the electric-field gradient spirals around the transverse spatial profile in ring-shaped beams called optical phase vortices (OPVs). Typically, the effect of a field advancing or receding due to geometric phase is relatively small and measured by a shift of interferometric fringes or scattering patterns. Here we reveal that the presence of geometric phase changes nonequilibrium phase transitions in a manner that can be generalized to interpret the nucleation of particles or waves with different angular momenta. When OPV’s develop azimuthal intensity modulations in isotropic self-focusing materials, electric fields with different OAM spatially separate and lead to sharp OAM switching dynamics. The changing torsional trajectories of light beams due to geometric phase are accompanied by the hydrodynamic migration of topological defects, which play a crucial role.


Wednesday, March 4, 2009, 17:00. Seminar Room