Section 7. ANGULAR MOMENTUM IN NONLINEAR OPTICS
In 1993 Basistiy et al. (7.1) examined the interaction of beams containing optical vortices with nonlinear materials and with computer generated holograms. In each case additional vortices, of either the same or opposite handedness, were found to appear in the beam. It was noted that when frequency doubled a beam with a ﬁrst order screw dislocation, that is l=1, acquired an additional screw dislocation.