Orbital-angular-momentum mixing in type-II second-harmonic generation by Leonardo J. Pereira, Wagner Tavares Buono, Daniel S. Tasca, Kaled Dechoum, Antonio Z. Khoury.

*We investigate the non linear mixing of orbital angular momentum in type II second harmonic generation with arbitrary topological charges imprinted on two orthogonally polarized beams. Starting from basic nonlinear equations for interacting fields, we derive selection rules determining set paraxial modes taking part interaction. Conservation naturally appears as charge rule. However, a less intuitive rule applies to radial orders when carrying opposite helicities are combined crystal, an intriguing feature confirmed by experimental measurements. *

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