ABSTRACT
Second harmonic generation (SHG) has been the most investigated nonlinear optical process, since its discovery by Franken in the 1960s [1]. In SHG processes the frequency of anincoming beam, ω, is doubled due to second-order optical susceptibility χijk( )2 (−2ω,ω,ω) of the nonlinear material. Within the electric-dipole approximation, the third-rank tensor χijk( ) ,2 or equivalently the d tensor components, dijk ijk= ( ) ( )1 2 2/ χ , present nonvanishing terms only if the material has a non-centrosymmetric crystal structure, that is, it belongs to a group symmetry without center of inversion, thus giving rise to the so-called bulk or electric dipole induced SHG. Several nonlinear optical techniques have been developed, in order to allow the different components of the third-rank tensor χijk( )2 to be determined with reference to a well-characterized sample, which is usually α-quartz, KDP, or BBO.
