Multiple quasi-phase-matching in nonlinear Raman-Nath diffraction.

The method of the superposition of a nonlinearity modulation is employed to design a two-dimensional (2D) nonlinear photonic lattice for efficient multiple quasi-phase-matched second harmonic generation in the process of nonlinear Raman-Nath diffraction (NRND). An analytical solution is proposed to calculate the second harmonic intensity in rectangular 2D lattices. This approach can be useful for the generation of multiple second harmonic beams with the efficiency a few orders of magnitude higher than in the case of nonphase-matched generation via NRND.