Structuring light beams via nonlinear diffraction in 3D nonlinear photonic crystal

We show that nonlinear diffraction in nonlinear photonic crystal offers a convenient way to generate structured light at new frequencies. To this end we fabricate a 3D nonlinear photonic crystal containing two layers of fork-shaped ferroelectric domain gratings. Illumination of the structure by a fundamental Gaussian beam leads to the generation of two co-propagating second harmonic vortices with opposite topological charges, whose subsequent interference forms Hermite-Gaussian (HG) beams in far field.