Mapping of the second-order nonlinear susceptibility of inhomogeneous absorbing media by Maker fringes analysis of optical difference mixing

This paper proves the possibility of and offers a technique for a unique reconstitution of the spatial profiles of various components of the complex second-order susceptibility tensor χ^(2)(z,ω1-ω2;ω1,-ω2) responsible for difference frequency generation in one-dimensionally inhomogeneous plates. To be able to achieve such reconstitution it is necessary to measure the complex amplitude of the reflected difference frequency wave in a certain range of incidence angles of the plane biharmonic wave with frequencies ω1 and ω2 in its spectrum. By altering the incidence plane of the initial biharmonic wave and/or the polarization of its monochromatic components it is possible to uniquely determine the coordinate dependences of more than a half of all second-order susceptibility tensor components. Such reconstitution is successful when the symmetric nature of the medium ensures the diagonal character of the linear dielectric permittivity tensor of the plate. Besides, the dielectric properties of the plate can change arbitrarily along the z axis. The suggested approach includes measuring the intensity of difference frequency waves generated under specific conditions with the use of an auxiliary reference plate to be able to avoid complex phase measurements.