THE SMART TRICK OF MAGNETO-OPTICAL CRYSTAL THAT NO ONE IS DISCUSSING

For an optical element with some birefringence, you can specify the retardance, that's the main difference in period shifts for the two polarization directions.All nonlinear crystals for nonlinear frequency conversion are birefringent. It's because they will have their nonlinearity only by being non-isotropic, and that also will cause birefringence