Fine-tuning of orbital angular momentum in an optical parametric oscillator

We investigate the dynamics of a type-II optical parametric oscillator pumped by a structured light beam carrying orbital angular momentum. Different operating regimes are theoretically derived and experimentally demonstrated, depending on the magnitude of the anisotropy imposed by the nonlinear medium. In a weakly anisotropic regime, fine-tuning of the orbital angular momentum transfer is obtained by adjusting the crystal parameters, such as temperature and orientation. Under strong anisotropy, orbital angular momentum transfer is not possible and the crystal tuning leads to an abrupt switching between different Hermite?Gauss transverse modes.