Abstract

The coupling between electromagnetic waves propagating in a nonlinear medium gives rise to a number of interesting phenomena. Specifically, the transfer of energy between two interfering laser beams and the accompanied generation of new beams (four wave mixing)¹ has been demonstrated in a wide class of materials. When two coherent pump waves intersect at a narrow angle in a Kerr medium, the resulting interference pattern perturbs the local refractive index and induces a grating. The writing beams scatter from the grating and can generate new diffracted beams. This process is known as forward degenerate four wave mixing (FDFWM). The first-order diffracted beam from each pump appears in the path of the other. The strongest spatially distinguishable order is the second. The second-order diffracted beams are not phase matched over significant propagation distances and so the energy associated with these orders is small. However, by introducing linear spacer layers into the nonlinear medium a grating of gratings can be formed as shown in Fig. 1. This permits phase matching, thus enhancing the diffracted side lobes.

© 1994 IEEE