Fourth harmonic generation via nonlinear diffraction in a 2D LiNbO3 nonlinear ph

Five conical harmonic beams are generated from the interaction of femtosecond mid-infrared (mid-IR) pulses at a nominal input wavelength of 1997 nm with a 2D LiNbO3 nonlinear photonic crystal with Sierpinski fractal superlattices. The main diffraction orders and the corresponding reciprocal vectors