Diagnostics of the inhomogeneous distribution of quadratic optical susceptibility over parametric scattering spectra

A new method is proposed for measuring the spatial distribution of the quadratic susceptibility of inhomogeneous nonlinear media. The method is based on the unique relation of the Fourier harmonics of this distribution with the shape of a signal-radiation line during parametric frequency conversion in a linear regime. The diagnostic possibilities of the method of spontaneous parametric scattering of light are analysed by simulating the spectra of nonlinear diffraction in layered structures with different profiles of variation in the quadratic susceptibility. The cases of step and smoothed variations in the susceptibility of periodically poled regular and irregular superlattices (structures formed by the layers of optically linear and nonlinear media) are considered and the effect of light absorption at an idler frequency is studied. The experimental spectra of periodically poled crystals are presented. Different methods for measuring the one-dimensional dependence of quadratic susceptibility on the coordinate in periodically poled structures and polydomain crystals are proposed.