ABSTRACT
Thus far in this book, we have examined nonlinear optical propagation in a wide variety of structures and media. We have examined forward and backward propagation of light due to induced reflection gratings in nonlinear materials, such as photorefractive (PR) crystals. In particular, we have seen in Chap. 9 how two-wave mixing is possible because of induced reflection gratings in PRmaterials. Also, in Chap. 11, we have seen howmultiwave forward and backward mixing in PR materials can give rise to self-organized patterns such as hexagons. The key point in both cases is that the reflection grating is induced; that is, the grating period is exactly one half of the wavelength of the contrapropagating light waves in the medium. Another way of stating this is to say that the grating vector length is twice the propagation constant of the light in the medium. In this case, there is perfect phase matching between the forward and the backward traveling waves, which gives rise to substantial reflected light.
