2ND-HARMONIC GENERATION BY REFLECTION OF A 2-DIMENSIONAL GAUSSIAN BEAM FROM THE SURFACE OF AN ISOTROPIC GYROTROPIC MEDIUM

A theoretical investigation is reported of the influence of the finite spatial size of a pump wave on second-harmonic generation by surface reflection of a two-dimensional Gaussian beam (treated as an example) incident on the surface of a nonabsorbing isotropic gyrotropic medium. Formulas are obtained for expressing the field of the reflected secon d-harmonic wave in terms of parameters representing the geometry of th e problem and in terms of the components of the material tensors which describe the quadratic optical response of the surface and the spatia l dispersion of the nonlinearity of the medium. It is shown that in th is case the doubled-frequency signal can be represented by a superposi tion of a two-dimensional Gaussian beam and a non-Gaussian component. This component appears most clearly for normal incidence of the pump w ave when second-harmonic generation is altogether impossible in the pl ane-wave approximation. The inhomogeneity of the surface region and th e spatial dispersion of the optical response of the medium are taken i nto account by adopting modified boundary conditions for an electromag netic field. These conditions include the surface density of the bound -charge current.