Subwave spikes of the orbital angular momentum of the vortex-beams in a   uniaxial crystal
  We have theoretically predicted the gigantic spikes of the orbital angular momentum caused by the conversion processes of the centered optical vortex in the circularly polarized components of the elliptic vortex beam propagating perpendicular to the crystal optical axis. We have experimentally observed the conversion process inside the subwave deviations of the crystal length. We have found that the total orbital angular momentum of the wave beam is conserved. 
T. Fadeyeva, C. Alexeyev, A. Rubass, A. Zinov'ev, V. Konovalenko and   A. Volyar
physics.optics