Multiorder nonlinear diffraction in frequency doubling processes.

We analyze experimentally light scattering from chi(2) nonlinear gratings and observe two types of second-harmonic frequency-scattering processes. The first process is identified as Raman-Nath type nonlinear diffraction that is explained by applying only transverse phase-matching conditions. The angular position of this type of diffraction is defined by the ratio of the second-harmonic wavelength and the grating period. In contrast, the second type of nonlinear scattering process is explained by the longitudinal phase matching only, being insensitive to the nonlinear grating period.