Nonuniform transverse distribution of the light intensity and polarisation upon sum-frequency generation from the surface of an isotropic gyrotropic medium in the case of normal incidence of light

Sum-frequency generation from the surface of an isotropic gyrotropic medium by two normally incident homogeneously elliptically polarised Gaussian beams is studied theoretically. Analytic expressions, completely describing the transverse spatial distribution of the intensity and polarisation in the cross section of the reflected beam at the sum frequency, were derived taking into account both the local and nonlocal contributions of the quadratic nonlinearity of the medium thicknesses and the nonlinear contribution of its surface. It is shown that a special selection of the parameters of the fundamental waves allows one to determine components of the surface susceptibility tensor.