Angular dependence of phase-matched second-harmonic generation in a photonic crystal

Experimental measurements of the second-harmonic-generation intensity in centrosymmetric photonic crystals indicate that the efficiency of this quadratic nonlinear process increases as the angle subtended by a reciprocal lattice vector and the second-harmonic field wave vector also increases. This behavior is explained by the use of a simple theoretical model based on second-harmonic generation from a lattice of nonlinear bilayers that confirms the surface character of this nonlinear process in this type of material.