Quasi-phase-matched second-harmonic generation under nonlinear diffraction conditions

An investigation is made of the principal characteristics of noncollinear quasi-phase-matched frequency doubling in the specific case of periodically poled lithium niobate. In the presence of an instability of the polarisation period, the use of a noncollinear geometry makes it possible to increase the conversion efficiency because of an increase in the effective interaction length when the incident radiation propagates at an acute angle relative to the layers of a nonlinear grating.